Bright X-Ray Sources in M31 Globular Clusters

a r X i v :a s t r o -p h /0106254v 2 4 F e

b 2002

A CCEPTED

FOR PUBLICATION IN THE

A STROPHYSICAL J OURNAL

Preprint typeset using L A T E X style emulateapj v.04/03/99

BRIGHT X-RAY SOURCES IN M31GLOBULAR CLUSTERS

R.D I S TEFANO 1,A.K.H.K ONG ,M.R.G ARCIA ,P.B ARMBY

Harvard-Smithsonian Center for Astrophysics,60Garden Street,Cambridge,MA 02138

J.G REINER

Astrophysical Institute Potsdam,14482Potsdam,Germany

S.S.M URRAY ,F.A.P RIMINI

Harvard-Smithsonian Center for Astrophysics,60Garden Street,Cambridge,MA 02138

Accepted for publication in the Astrophysical Journal

ABSTRACT

We have conducted Chandra observations of ～2560square arcmin (～131kpc 2)of M31,and ?nd that the most luminous X-ray sources in most of our ?elds are in globular clusters.Of the 28globular cluster X-ray sources in our ?elds,15are newly discovered.Approximately 1/3of all the sources have L X ([0.5–7]keV)>1037ergs s ?1;approximately 1/10of all the sources have L X ([0.5–7]keV)close to or above 1038ergs s ?1.The most luminous source,in the globular cluster Bo 375,is consistently observed to have L X greater than 2×1038ergs s ?1.(1)We present data on the spectra and/or light curves of the 5most luminous M31globular cluster sources.

(2)We explore possible explanations for the high X-ray luminosities of the brightest sources.These include that the X-ray sources may be composites,the radiation we receive may be beamed,metallicity effects could be at work,or the sources may be accreting black holes.We weigh each of these possibilities against the data.In addition,we introduce a neutron star model in which mass transfer proceeds on the thermal time scale of the donor star.Our model can produce luminosities of several times 1038ergs s ?1,and leads to a set of well-de?ned predictions.

(3)We compute the X-ray luminosity function and the distribution of counts in wavebands that span the range of energies to which Chandra is sensitive.We ?nd the peak X-ray luminosity is higher and that systems with L X >1037erg s ?1constitute a larger fraction of all GC sources than in our Galaxy.

(4)We study the possible reasons for this difference between M31and Galactic globular cluster X-ray sources and identify three promising explanations.

Subject headings:galaxies:individual (M31)—globular clusters:general —X-rays:galaxies —X-rays:stars

1.INTRODUCTION

1.1.X-Ray Sources in Galactic and M31Globular Clusters

1.1.1.Galactic Globular Cluster X-Ray Sources X-ray studies of Milky Way (MW)globular clusters (GCs)suggested that they be divided into “bright"(L X >1035ergs s ?1)and “dim"(L X <1034ergs s ?1)sources (see e.g.Hertz &Grindlay 1983;Verbunt et al.1985;Deutsch et al.2000).The majority of dim sources are thought to be accreting white dwarfs (Di Stefano &Rappaport 1994;Hakala et al.1997;Grindlay et al.2001).Chandra observations with realistic exposure times can only see evidence of large populations of dim sources in M31,not individual sources.We can therefore draw comparisons only between the bright GC sources in each galaxy.Twelve MW GCs house bright X-ray sources;until re-cently,no cluster was known to have more than a single bright source

2.There is evidence,largely from X-ray bursts,that the bright MW GC sources are accreting neutron stars.There is no evidence that any MW GC harbors an accreting black hole.Indeed,this apparent lack of black holes in MW GC has been commented upon and explained as perhaps due to large kick velocities obtained by BH binaries upon interactions with other GC members (Sigurdsson &Hernquist 1993;Kulkarni et al.1993).The most luminous MW GC X-ray source (4U 1820–30

in NGC 6624)has L X ～1?5×1037ergs s ?1(see Bloser et al.2000for a review).

1.1.

2.M31Globular Cluster X-Ray Sources

We have conducted Chandra observations of ～2560square arcmin (～131kpc 2)of M31,and ?nd that the most luminous X-ray sources in most of our ?elds are in globular clusters.Of the 28globular cluster X-ray sources in our ?elds,15are newly discovered.Approximately 1/3of all the sources have L X ([0.5–7]keV)>1037ergs s ?1;approximately 1/10of all the sources have L X ([0.5–7]keV)close to or above 1038ergs s ?1.The most luminous source,in the globular cluster Bo 375,is consistently observed to have L X greater than 2×1038ergs s ?1.Given the sensitivity of the detectors we used (ACIS-S and ACIS-I),and our exposure times (15ksec and 8.8ksec,respec-tively),we could have detected sources with luminosities as low as 1.5?5×1035ergs s ?1,and indeed have discovered some sources only slightly brighter than these limits.The large frac-tion of globular cluster sources with L X >1037ergs s ?1stands in sharp contrast with the situation in the Galaxy,where,e.g.,only one of the 11bright sources studied in the ROSAT all-sky survey had L X >1037ergs s ?1(Verbunt et al.1995).

Each of the following subsections (§1.2?1.6)provides an overview of the corresponding section (§2?6)of the paper.

1also Department of Physics and Astronomy,Tufts University,Medford,MA 02155

2White

&Angelini (2001)recently used Chandra to resolve two distinct luminous X-ray sources separated by <3′′in the massive post-core-collapse MW GC,

M15.

1

2

1.2.Bo375:the highest-luminosity X-ray source in a globular

cluster

While conducting a census of M31X-ray sources,we found

that the most luminous source in our census was associated with

the globular cluster Bo375.Our observations were performed using the ACIS-S detector aboard the Chandra X-Ray Obser-

vatory.The uncertainty in the position of the source is～1′′, comparable to the uncertainty in the cluster position from the Bologona catalog(Battistini et al.1997).Since the density of

X-ray sources in the region around the source is not very high

(there is just one other source with L～1036erg s?1within5′), it is likely that the X-ray source is physically associated with Bo375.The measured luminosity(between0.5and2.4keV) of this source is between～2?5×1038ergs s?1.In§2we present new data on the?ux,spectrum,and light curve of the X-ray source,Bo375.In addition,we place these observations in perspective by summarizing and,in some cases re-analyzing, data from previous X-ray observations of the source.Although the spectrum and/or light curve of Bo375was studied in2ear-lier papers(Supper et al.1997;Irwin&Bregman1999),the source luminosity is not quoted in the literature.We?nd,how-ever,that,like our own observation,all previous observations of the X-ray?ux,which is variable,are consistent with lumi-nosities that range from～2×1038ergs s?1to～5×1038ergs s?1.That is,barring beaming effects,the luminosity is most likely super-Eddington for a1.4M⊙accretor.This would make Bo375an interesting source whatever its location,but its po-sition within or very near to a globular cluster(GC)makes it even more special.This is because,as mentioned above,the maximum luminosity observed for a MW GC X-ray source is4 times smaller than the minimum luminosity found for Bo375. In§2we also explore possible physical reasons for the observed high luminosity of this source.

1.3.Other Bright M31GC X-Ray Sources

The second and third most luminous X-ray sources in our sample are also associated with globular clusters,and one of these sources also exhibits X-ray luminosity close to1038ergs s?1.The?elds we were surveying are shown in Figure1,su-perposed on an optical image of M31.Because the existence of several luminous sources suggests a more general phenomenon, we have considered an additional data set,collected during 1999and2000by the combination of Chandra’s HRC,ACIS-I, and ACIS-S.The combined data sets include10globular clus-ter X-ray sources with L X>1037ergs s?1.The spectra and light curves of4of these sources are presented in§3.The light curves of these sources(and also of Bo375),exhibit enough structure on short time scales that it is clear that at least one source in the cluster must have a luminosity that is a signi?cant fraction of the total luminosity we have observed.

1.4.Population Studies

These high-luminosity sources raise questions about possible differences between the luminosity function of globular cluster X-ray sources in M31and that of the Milky Way.We there-fore,in§4,construct the luminosity function of the M31glob-ular cluster X-ray sources as measured by Chandra,and com-pare it to the luminosity function of Milky Way globular clus-ter sources detected during the ROSAT all-sky survey(Verbunt et al.1995).

1.5.M31’s Globular Clusters

The primary differences between the population of X-ray sources in M31globular clusters and those in Galactic globular clusters are that(1)the peak luminosity is higher,and(2)the high-luminosity end of the distribution function is more popu-lated.It is natural to ask if these differences can be explained by differences in the two galaxies’populations of globular clus-ters.This question is addressed in§5.

1.6.Conclusions:Possible Explanations Explanations are required at two levels:(1)what is the nature of the sources that appear to be so highly luminous?(2)what properties of M31and its system of globular clusters generate these bright sources?These issues are the focus of§6.

2.BO375

2.1.Observations and Data Reduction

Bo375has been observed by several X-ray missions.A sum-mary of the X-ray observations used here is given in Table1. Bo375was?rst observed with Einstein in1979during a sur-vey of M31and then it frequently appeared in the ROSAT M31 survey data from1991to1994.It was also observed with ASCA in1993and Chandra in2000and2001.We therefore have ob-servations spanning an interval of more than20years,and can study the spectrum and the time evolution of the source.

2.1.1.Previous X-ray Observations

Einstein Data—Bo375was observed with Einstein High Resolu-tion Imager(HRI)in1979during M31survey observations.The Ein-stein HRI has a spatial resolution of～3′′,and no spectral resolution. The count rate was extracted from a18′′radius circle centered on the source centroid and the count rate is～0.03counts s?1,corresponding to～5×1038ergs s?1in0.5–10keV(assuming a power-law model with N H=1021cm?2,α=1.7and a distance of780kpc;Macri et al. 2001).For full details on source counts and background extraction and events corrections we refer to Fabbiano(1988).

ROSAT Data—For the energy spectra of Bo375,we only analyzed only long(>20ksec)observations.There are three long observations in the archival database,and two of them(ROSAT#2and ROSAT#3) are just outside the‘rib’support structure at18′from the center of the ?eld.The remaining one(ROSAT#1)is～14′off-axis.Each spectrum was extracted from a circular aperture centered on the source.The size of the extraction radius varied from7′′to9′′with the off-axis angle of the source to account for the point-spread function of the instrument. Background was subtracted from an annulus centered on the source. The spectra were binned so that there are at least20photons in each energy bin,and all channels below0.1keV and above2.4keV were ignored.

ASCA Data—The Advanced Satellite for Cosmology and Astro-physics(ASCA)satellite(Tanaka et al.1994)is equipped with two Solid State Imaging Spectrometers(SIS;0.4–10keV)and two Gas Imaging Spectrometers(GIS;0.7–10keV).For our purpose,we only used the data taken by GIS instruments,because the source was near the edge of SIS.ASCA observed Bo375on1993July29.Standard data screening was employed3.Data taken at a geomagnetic cut-off rigidity lower than4GeV,at an elevation angle less than5?from the Earth’s limb,and during passage through the South Atlantic Anomaly were rejected.After?ltering,the total net exposure time of each GIS was16.2ksec.We extracted the GIS spectra from a circular region of radius6′centered at the position of the source,while the back-ground was extracted from an annulus region around the source.We have searched for any contamination from other X-ray sources within

3See the ASCA Data Reduction Guide2.0(https://www.sodocs.net/doc/f45904412.html,/docs/asca/abc/abc.html)

3

F IG.1.—The regions observed by the M31AO2GO census overlaid on an optical Digitized Sky Survey image of M31.North is up,and east is to the left.The chip orientation is shown for the15ksec observations that occurred in November2000.Subsequent observations have rotated by90?and then a further120?.Each aim-point(always in S3)is marked by a cross(×).

4

TABLE1

O BSERVATION LOG OF B O375

Date Observatory Instrument Exposure Count rate Remarks

(ksec)(c/s)

NOTES—This list includes only those observations we have used in this paper.

10′;there are only a few very faint sources in the ROSAT PSPC cata-log(Supper et al.1997)and in our Chandra observation.Hence any contamination would be minimal.Spectra were rebinned to have at least20photons in each energy bin and we?tted the GIS2and GIS3 spectra simultaneously.We also set the normalization of GIS3to be a free parameter to account the difference in the calibration of the two detectors.In all?ts the GIS3normalization relative to GIS2is about 5%.

2.1.2.Chandra Observations

Bo375was located in the?eld of an ongoing(GO–AO2)X-ray census of M31.It was observed on2000November1for13.8ksec. The Advanced CCD Imaging Spectrometer(ACIS-S)was in the focal plane and Bo375was located in the ACIS-S2chip and was～4.4′from the aim-point.Data were extracted from0.3–7keV to minimize the background,and a circular extraction region of radius6′′centered at the source position was used.Background was also extracted from an annulus region centered on the source and it contributed less than 0.1%.The source spectrum was rebinned so that there are at least20 photons in each energy bin in order to allowχ2statistics.The re-sponse matrix and the ancillary response?le were generated by CIAO v2.14.We note that the Chandra spectrum suffers signi?cant pile-up (～30%).

In addition,a sequence of short(0.8ksec to2ksec[see Table 1])High Resolution Camera(HRC)exposures was available,because Bo375happened to be imaged during more than one year of monitor-ing carried out as part of a GTO program(see Garcia et al.2000).In these images,Bo375was～10′off-axis.We have extracted the light curve of the source from a25′′circular region centered on the source position.

2.2.Spectral Analysis and Results

The spectra for the ROSAT,ASCA and Chandra data were?tted with a variety of spectral models using XSPEC v115.We?rst tried to?t the spectra with single-component models including absorbed power-law,black-body,thermal bremsstrahlung,disk black-body and cut-off power-law models.Power-law models provide good?ts to each data set,except the Chandra ACIS-S data.Derived values of photon index range from1.3to1.7,with N H～(1?3)×1021cm?2.The Galac-tic hydrogen column in the direction of M31is about7×1020cm?2

(Dickey&Lockman1990),and therefore our results are consistent

with additional local absorption,either due to M31itself or to absorp-

tion within the system.An absorbed black-body model gave a value

of N H(～3×1020cm?2)smaller than the Galactic value for all obser-

vations,and we therefore discarded this model.We also?t the data to

thermal bremsstrahlung,cut-off power-law,and disk black-body mod-

els;these?ts gave very large uncertainties for the ROSAT and ASCA

data,and the?t was unacceptable(χ2ν～1.4)for the Chandra data. Results of spectral?ts to single-component models are shown in Ta-

ble2.The errors correspond to90%con?dence levels for a single

interesting parameter.

We next tried to?t the spectra with different two-component mod-

els.A black-body plus power-law model gave an acceptable?t(χ2ν=

1.27)for the Chandra data;for the ASCA data,the additional black-

body component does not improve the?t signi?cantly(at the99%

level),indicating that the black-body component is soft(<1keV).To

check the?t of the Chandra data,we also?tted the ROSAT and ASCA

data simultaneously so that we have broad energy coverage from0.1–

10keV.Since Bo375is a variable,we choose the ROSAT observation

with?ux level similar to that of the ASCA data.The0.5–2.4keV?uxes

of ROSAT#1and ROSAT#2were～4%lower than the ASCA observa-

tion.ROSAT#2is close to the‘rib’and there are shadowing effects.

We therefore used ROSAT#1for the joint spectral?ttings.A single

power-law model gave a reasonable?t to the data,and a black-body

plus power-law model did improve the?t(χ2ν=1.16).We replaced the

power-law component with a cut-off power law.However,it did not

give a better?t and the cut-off energy is larger than10keV,indicating

that the cut-off energy is much higher than10keV and is therefore not

accessible to either ASCA or Chandra.

Note that the spectral?t to the Chandra data may be affected by

pile-up,which we have estimated to be at the30%level.Normally

one would expect pile-up to yield a somewhat harder spectrum than

the true emitted spectrum.In fact,the values ofαand k T derived

form the Chandra data are in good agreement with those derived from

the combined ROSAT/ASCA?t,which does not suffer from pile-up. The higher value of N H in the Chandra?t may,however,be related to the effects of pile-up.

We also employed a disk black-body component instead of black-

4https://www.sodocs.net/doc/f45904412.html,/ciao/

5https://www.sodocs.net/doc/f45904412.html,/docs/xanadu/xspec/index.html

5

body,it gave a equally good?t(χ2ν=1.17)but with larger errors on all

√

parameters.The derived inner radius of the accretion disk R in

6

F IG.2.—Chandra ACIS-S spectral?t of Bo375.The spectrum was?tted by an absorbed power law plus blackbody model(N H=3.35×1021cm?2,α=1.67 and kT=0.80keV)The observed luminosity(0.3–7keV)at780kpc is4.2×1038ergs s?1.

F IG. 3.—Joint ROSAT and ASCA spectral?t of Bo375.The spectrum was?tted by an absorbed power law plus blackbody model(N H=1.61×1021cm?2,α=1.61and kT=0.86keV)The observed luminosity(0.3–7keV)at780kpc is6.1×1038ergs s?1.

7

TABLE2

B EST-FIT PARAMETERS FOR THE ENERGY SPECTRA OF B O375

√

Observation N HαkT a R in

ROSAT#10.96±0.961.33±0.08 1.32/156 2.16

ROSAT#20.98±0.151.30±0.11 1.01/147 2.34

ROSAT#31.10±0.201.32±0.120.90/148 1.43

ASCA2.20±0.601.70±0.070.90/81 2.25

Chandra3.91±0.161.67±0.03 1.53/209 1.42

3.35±0.341.67±0.130.80±0.11 1.40/207 1.44

ROSAT#1+ASCA1.20±0.901.58±0.04 1.22/238 2.29

1.61±0.081.61±0.080.86±0.12 1.16/236

2.29

1.10±0.201.77±0.341.95±0.3510±6.2 1.17/236

2.28

√

A ti(A ti?

8

Light Curve

Bo 375

10

20

30

Random

20

30

40

50

60

150

200

250

50100150200

300

350

400

450

time (minutes)

50100150200

time (minutes)

F IG.4.—The light curves of Bo375binned into intervals of0.5min,1min,5min and10min.Clearly there is no evidence for time variability on the time scale of the Chandra observation.See§2.4.4for discussion.

the central16′×16′region around the galaxy from1999-2000.For

the analysis below,we used8.8ksec from the longest pointing(1999

October13),except that two additional GCs were observed on1999

December11and2000January29.

3.2.The Sources

Table3provides a complete list of all of the X-ray sources we have

observed in M31globular clusters.The sources are listed in order of

count rate;the source with the highest count rate appears?rst.For each

source,the coordinates(J2000),optical ID and luminosity(assuming

a power law model with N H=1021cm?2and photon indexα=1.7)

are included.Three sources(Source2,13and15)have been observed

by two GO pointings and we list both observations with the?rst one

corresponding to the earlier observations.Table4lists the counts in a

sequence of energy bins.

Optical IDs:A wavelet detection algotithm(WAVDETECT in CIAO)

was used to?nd X-ray sources.Each Chandra source was placed at

the center of a3′′source region.We cross-correlated with catalogs of

globular clusters(Battistini et al.1987;Magnier1993;Barmby et al.

2000;Barmby&Huchra2001).Typical offsets between the globular

clusters and our X-ray sources are about1′′;when a cluster appears in

multiple catalogs,the offsets may differ somewhat.

3.3.Hardness Ratios and Spectra

In order to quantify the spectral behavior of M31X-ray GCs,we

complied a table for the counts in different energy bins(see Table4).

The bins we use are0.1?0.4,0.5?0.9,0.9?1.5,1.5?2.0,2?4,and

4?10keV,respectively.The choice of ranges for the low-energy bins

is based on the ROSAT bins typically used for these data sets(Verbunt

et al.1995,Supper et al.1997),so as to facilitate comparisons between

Chandra and ROSAT data sets.The count rates in each bin are back-

ground subtracted.

We implemented a set of spectral?ts for each source with more

than～400counts(0.3–7keV).There are4such sources(in addition

to Bo375)and a total of5observations with such count rates.They

are:Bo82with3053counts in the?rst GO pointing and2277counts

in the second pointing,Bo153with962counts in a GTO pointing with

ACIS-I,Bo86with542counts(also in a GTO pointing with ACIS-I),

and Bo143with446counts.

We?rst tried to?t the spectra with a power law model with the hy-

drogen column density N H as a free parameter.If the derived N H was

inconsistent with the observed color excess E(B?V)from optical ob-

servations,then we?xed the N H according to the optical absorption.

We also tried to?t the spectra with other single component models

such as blackbody and thermal bremsstrahlung model.All of the?ts

were either unacceptable(χ2ν>2),or also the best-?t parameters were

unrealistic.Finally,we?tted the spectra with power law plus black-

body models.Although these generally gave good?ts,the blackbody

temperature became unrealistic and the?ts were not improved signi?-

cantly.We describe below the best?t parameters of power law models.

Bo82–A power law model provied a good?t(χ2ν=1.03/114dof)

for the?rst GO observation with N H=(5.17±0.31)×1021cm?1and

α=1.42±0.06.The emitting luminosity in0.3–7keV is1.70×1038

erg s?1.For the second GO observation,we obtained N H=(4.58±

0.40)×1021cm?1andα=1.14±0.07,withχ2ν=1.16/88dof.The

luminosity is2.20×1038erg s?1.

Bo153–The best?t parameters were N H=(1.07±0.33)×1021

cm?1andα=1.38±0.10,withχ2ν=0.92/40dof.The luminosity in

0.3–7keV is9.12×1037erg s?1.Fixing the hydrogen column den-

sity N H=6×1020cm?2[E(B?V)=0.11]gaveα=1.26±0.05with

χ2ν=0.96/41dof.

9

TABLE3

G LOBULAR C LUSTER X-RAY S OURCES IN M31

ID Source Name R.A.Dec.Exposure L X(0.3–7keV)Optical ID

(h:m:s)(?:′:′′)(ksec)(1037erg s?1)

NOTES—Observations lasting longer than10ksec were carried out as part of the GO program(see Figure1);Shorter

observations around the central16′×16′?eld were carried out as part of the GTO program(Garcia et al.2000;

Primini et al.2000).

?Source detected by ROSAT(Supper et al.1997)

?Source detected in both GO observations

?Results based on an HST survey(Barmby&Huchra2001)

*Source25is associated with two clusters:mita165and mita166

10

TABLE4

C OUNTS IN DIFFERENT ENERGY BANDS OF G LOBULAR C LUSTER X-RAY S OURCES IN M31

Source Counts Hardness

0.1–0.4keV0.5–0.9keV0.9–1.5keV 1.5–2keV2–4keV4–10keV Ratio a

a Hardness ratio is de?ned as2–10keV/0.5–1.5keV

11

F I

G .5.—15ksec Chandra ACIS-S light curve of Bo 375.The time resolution is 1000

sec.

F I

G .6.—Chandra HRC light curve of Bo 375.The luminosity was estimated by PIMMS,using the observed count rate and assuming a power law spectral model with N

H =1021cm ?2and photon index α=1.7.

Bo 86–Leaving the column density as a free parameter,a power law model provided a good ?t with χ2ν=1.05/22dof.The best-?t param-eters were N H =(1.28±0.50)×1021cm ?2and α=1.37±0.15.The luminosity in 0.3–7keV is 5.26×1037erg s ?1.We have ?xed the ab-

sorption at N H =4.4×1020cm ?2[E (B ?V )=0.08]and we obtained α=1.15±0.08with χ2ν=1.15/23dof.

Bo 143–A Power law is the only model which can be ?tted for the spectrum.We have obtained N H =(1.96±0.66)×1021cm ?1and

12

α=1.90±0.23,withχ2ν=0.69/12dof.The luminosity in0.3–7keV is 3.17×1037erg s?1.By?xing the absorption at N H=7.2×1020cm?2 [E(B?V)=0.13],the best?t parameters wereα=1.50±0.10and χ2ν=1.02/13dof.

Except for the second observation of Bo82,the power-law photon indexαranges from1.4to2which is typical for low-mass X-ray bina-ries.For Bo82,the photon index changed from1.4to1.1,indicating a transition from a soft state to hard state but at a similar intensity level. Trinchieri et al.(1999)also found that Bo82to be a hard source and on that basis conjectured that it might be a black hole.ROSAT also observed Bo82(see Supper et al.1997);we reanalyzed the archival data and a power-law withα～1.4gave a good?t to the data.

We have constructed the time history of these four sources over ～500days(see Figure7).Just as for Bo375,Bo82and Bo86show intensity variability by a factor of～3.In particular,Bo86may have long-term variability on timescales of～200days.Bo153and Bo143 may be variable at a lower level but higher signal-to-noise light curves would be needed to establish variability.

4.POPULATION STUDIES

4.1.The Luminosity Function

Two types of information can be used to construct a luminosity function.First,of course,is the observed luminosities of the sources. This is the information we present in this paper,because our primary motivation is to feature the high-luminosity sources that have actually been detected and to compare the detected GC X-ray sources in M31 with detected GC X-ray sources in the Milky Way.It is also possible to take a more comprehensive view that takes into account the fact that we learn something about the luminosity function from computing up-per limits for clusters which have been observed with X-ray detectors but within which no X-ray sources were discovered.Ongoing and pos-sible new observations may extend the depth of M31observations and their sensitivity to transient GC X-ray sources.Thus,a more complete picture of the M31globular cluster X-ray sources is developing,and will warrant a later careful look at non-detections as well as detections.

In Figure8we present the luminosity distribution of all30GC X-ray sources observed by Chandra.Luminosities were derived as-suming a power-law model with N H=1021cm?2andα=1.7in0.3–7 keV.The derived luminosities are not very sensitive to the spectral parameters;the difference is about20%when varying the N H from 6?15×10?22cm?2andαfrom1.2to2.The thermal Bremsstralung model used by Primini,Forman,&Jones(1993)gave luminosity dif-ferences up to80%.

This luminosity function has2quanti?able differences with the Galactic GC X-ray luminosity function,even though the most recently published M31GC luminosity function found the M31and Galac-tic GC X-ray luminosity functions to be in agreement(Supper et al. 1997).First,the peak X-ray luminosity is higher by a factor of～10, and second,a larger fraction of all GC sources have luminosities above 1037erg s?1(～10/30in M31,vs1/12in the Galaxy).

4.2.Previous Work

The discovery of high-luminosity sources in M31X-ray sources be-gan roughly25years ago.Twenty one X-ray sources discovered by instruments aboard the Einstein observatory were tentatively identi-?ed with globular clusters.The source identi?ed with the cluster la-beled by Sargent et al.(1977)as307,which we have referred to as Bo375,had a measured X-ray luminosity of2.7×1038ergs s?1.The source identi?ed with Bo135had a measured X-ray luminosity of 1.1×1038ergs s?1.Long&van Speybroek(1982),noted that these lu-minosities were higher than any observed for Galactic GCs.Battistini et al.(1987)further noted that the fraction of then-known M31GCs with X-ray sources might also be larger than the fraction our Galaxy. This was because,even though the measured fractions were similar, only the most luminous of the Galactic sources could have been de-tected in M31by Einstein.This raised the question of whether the frequency of X-ray sources in M31was generally higher,or whether the GC X-ray sources in M31were brighter than Galactic GC sources. Observations of the central～34′of M31with ROSAT’s HRI discov-ered18GC X-ray sources and placed upper limits on X-ray detec-tion from32additional globular clusters(Primini,Forman,&Jones 1993).All of the measured X-ray luminosities were below1038ergs s?1,but8were above1037ergs s?1.A statistical analysis,based on sur-vival analysis techniques(Avni et al.1980,Feigelson&Nelson1985, Schmitt1985)allowed the upper limits as well as the measured lumi-nosities to be used to construct the luminosity function.This procedure produced a cumulative X-ray luminosity distribution that exhibited a maximum luminosity consistent with that of the Galactic GC X-ray luminosity distribution,but which seemed to have a larger population of high-luminosity sources.The most comprehensive survey to date is the1991ROSAT survey of M31,which detected31globular clus-ter X-ray sources(Supper et al.1997;see also Supper et al.2001).

A statistical analysis that paralleled the one carried out by Primini et al.(1993)agreed that the maximum luminosity of M31globular clus-ter sources is consistent with that of that of Galactic globular cluster sources.Based on this larger sample,however,it was concluded that there is no difference between the luminosity functions of M31and Milky Way globular clusters.

Given the shifts in perception of the M31GC luminosity function, we note that the higher-X-ray luminosities(>1038erg s?1)are well established in the Chandra data sets and in prior X-ray data.Overall, using PIMMS to convert measured count rates to X-ray luminosities for the power-law model used to construct the Chandra-measured lu-minosity function,we?nd that there are～7sources across data sets with X-ray luminosities near or above1038erg s?1.

Even the result about the large fraction of sources with L X>1037 erg s?1is likely to remain valid when additional observations of M31 GCs are carried out.To justify this statement,we?rst note that already-completed observations taken by other X-ray telescopes can be used to extend the Chandra sample,and that the extended samples exhibit this same characteristic.For example,the ROSAT data on18 GC X-ray sources(Supper et al.1997,2001)that are not in our?elds includes6GCs with L X[0.3-7keV]between1036and1037erg s?1, and12GCs with L X[0.3-7keV]>1037erg s?1.Second,we note that the only way for the fraction of sources with L X[0.3-7keV]to be reduced to the Galactic value would be if a very large number of M31GCs were discovered to house lower-luminosity bright sources (10351035 erg s?1)to bring the fraction of L X[0.3-7keV]>1037ergs s?1sources into line with the Galactic value(1/12),we would have to?nd～200 such sources.In this case,the fraction of M31GCs with X-ray sources would lie somewhere between1/2?1.The contrast between this value and the value of～1/10for Galactic GCs which house bright X-ray sources would itself prove interesting.

4.3.Spectral Comparisons

Since our data and analysis show that there are clear differences in the luminosity functions of the Galactic and M31globular cluster X-ray sources,it is important to compare the source spectra as well.Be-cause of the greater distance of M31,we can at present only compare the spectra of its most luminous clusters with the spectra of Galactic GC sources.In addition,the M31GC X-ray spectra collected so far, even for these bright sources,generally have fewer counts,making di-rect comparison with the best Galactic GC data dif?cult.Furthermore, if some of the bright M31GC sources we observe are actually compos-ites of separate sources,blending may further complicate the compar-isons.Despite these caveats,it is important to make a?rst step toward the systematic comparison of spectra.Future observations which can provide better spectral and spatial resolution will allow more detailed and meaningful comparisons to the model.

4.3.1.M31

13

F I

G .7.—Chandra HRC light curves of Bo 82,Bo 153,Bo 86and Bo 143.The two ACIS-S pointings of Bo 82are also included in the plot (solid squares).The luminosity was estimated by the best-?tting spectrum which derived from ACIS pointings.To compute its luminosity,we assumed Bo 82to be in its soft state (α=1.4).

We used the ?ts to the ACIS-S observations described in §3.All sources,except Bo 82,as seen in an ACIS-S observation on 2001March 8,can be ?tted by a single power law model with α=1.4?1.9.The Bo 82spectra exhibited a somewhat harder (α=1.1)spectrum.Previous BeppoSAX observations provide another important resource.Trinchieri et al.(1999)showed that 8of the M31GC candidates spectra can be ?tted with either a power law (α=0.8?1.9)or a bremsstrahlung (kT =6?9keV)model in 1.8–10keV .Two of them (Bo 82and Bo 158)have somewhat harder spectra with α～1.Both the spectral ?t of our Bo 82data (§3)and the binned count rates shown in Table 4,demonstrate that these two sources are relatively harder than the others.Therefore the BeppoSAX observations appear to be consistent with ours,although source confusion could complicate the comparison.

https://www.sodocs.net/doc/f45904412.html,parisons with the Milky Way

Callanan et al.(1995)found from archival EXOSAT data that 5out of the 6Galactic GCs can be well ?tted with a power law plus blackbody spectral model (α=1.6?2,kT =0.5?1.5keV).Our high signal-to-noise Bo 375spectra are consistent with their results.

In a recent study of GCs in our Galaxy using BeppoSAX ,Sidoli et al.(2001)showed that the X-ray spectra of GCs can extend up to 20–100keV and they can be ?tted with a black-body (or disk black-body)plus Comptonization model.We here found the M31GC sources also have hard X-ray tails up to ～10keV (which is the limit of both ASCA and Chandra ).We have also tried to ?t the spectra of Bo 375with COMPTT and COMPST models used by Christian &Swank (1997)and Sidoli et al.(2001);the parameters were not constrained and the Comtonizing plasma temperature (kT e )has a very large value (～100keV).This indicates that kT e is above 10keV ,which is also seen in

GCs in our Galaxy (e.g.,Sidoli et al.2001).

To facilitate the comparison between M31sources and Galactic sources,we reanalyzed all the archival BeppoSAX Galactic GCs used by Sidoli et al.(2001).The reason for using BeppoSAX data is that it covers more samples and has a common energy range with Chandra .We used an absorbed power law model (with N H ?xing at the optical determined value).We also restricted the ?t to energies ranging from 2–7keV for both data sets.The reason for this is that absorption plays a signi?cant role in shaping the observed spectrum from some of the Galactic sources;we wished to compare the Galactic and M31sources across a range of energies in which absorption is not important.Ta-ble 5shows the results of the BeppoSAX spectral ?ts together with the Chandra ?ts on M31sources in the same energy range.Although the ?ts are unacceptable for some cases,and are not expected to corre-spond to the true physical models,due to our limited energy range,the derived αis in the range of 1.4–2.5,while M31sources have values between 1.4and 1.9.These results are in good agreement,although the sample size of M31sources is limited.We also used PIMMS to estimate the Chandra count rate for a single power law spectrum with α=1.4?2and N H =1021cm ?2and calculated the hardness ratio (2–10keV/0.5–1.5keV).The hardness ratio ranges from 0.4to 0.8which is consistent with most of the values shown in Table https://www.sodocs.net/doc/f45904412.html,bining the M31GC sources observed with BeppoSAX in 1.8–10keV (Trinchieri et al.1999),we conclude that the X-ray spectral properties of M31GCs and Galactic GCs above 2keV are roughly the same.

These comparisons make it clear that,in spite of signi?cant lumi-nosity differences,the conjecture that the M31globular cluster X-ray sources have spectra similar to those of the Galactic GC sources is still viable.Nevertheless these broad band comparisons are not able to ei-ther establish a neutron star nature or rule out a black hole nature for

14

F IG.8.—Luminosity functions for M31globular clusters and Galactic clusters.The solid curve represents the M31clusters and the dashed curve is the distribution of the Galactic sources(Verbunt et al.1995).

TABLE5

B EST-FIT S PECTRUM(2–7KE V)OF G ALACTI

C AN

D M31G LOBULAR C LUSTERS

Source Distance N Hαχ2ν/do f

(kpc)(1021cm?2)

NOTES—see§4.3.2for discussion.

15

the sources.The need for further observations is emphasized by the fact that observations of Bo82have found it to be sometimes in a lu-minous soft state,similar to Galactic GC sources,and sometimes in a luminous hard state.

5.THE M31GLOBULAR CLUSTER SYSTEM VS THE MILKY WAY’S

CLUSTERS

The fact that X-ray binaries are as luminous as the ones we have studied in M31globular clusters is not problematic.These sources do present a puzzle,however,when we compare them to globular cluster X-ray sources in our own Galaxy.The primary differences between the population of X-ray sources in M31globular clusters and those in Galactic globular clusters are that(1)the peak luminosity is higher, and(2)the high-luminosity end of the distribution function is more populated.It is natural to ask if these differences can be explained by differences in the two galaxies’populations of globular clusters.

There is one obvious difference between the globular cluster sys-tems of M31and the Milky Way:M31has more globular clusters. With～150well documented Galactic globular clusters,the total pop-ulation could be larger by～20(Minniti1995).The total number of M31globular clusters is less certain,but there are over200con?rmed clusters(Barmby et al.2000)and the total population could be～>400 (Battistini et al.1993).On a practical level,the greater distance to clusters in M31has made it dif?cult to learn as much about individual clusters as we know about Galactic globular clusters.HST has enabled studies of M31globular cluster morphology(Bendinelli et al.1993) and stellar populations(Ajhar et al.1996),although not at the same level ground-based studies have achieved for globular clusters in our own Galaxy.HST studies,which have concentrated on the brightest M31globular clusters,?nd no obvious differences between the prop-erties of these clusters and those of the brightest Milky Way clusters. Ground-based observations of M31globular clusters have provided a wealth of information about integrated luminosities,colors,and spec-troscopic features of the population as a whole.The result of these studies is that the globular clusters of M31are similar in most respects to those of the Galaxy.Differences tend to be subtle:for example, M31GCs are overabundant in CN compared to Milky Way GCs of the same metallicity(e.g.,Burstein et al.1984).The M31globular cluster luminosity function also shows evidence for variation not seen in the Milky Way GC luminosity function:the inner clusters are on average, brighter than the outer clusters,and the metal-rich clusters are brighter than the metal-poor clusters(Barmby,Huchra,&Brodie2001).As-suming the GC luminosity function differences are real and not caused by catalog incompleteness,they could point to age or mass variations in the M31GCs(see§6).

5.1.Fraction of Clusters with X-ray sources:Radial

Dependence

Since we have imaged four?elds at different locations in M31,we can examine the fraction of clusters with X-ray sources as a function of projected distance from the center of the galaxy.To do this,we used the GC catalogs to determine which clusters fell into the region of sky covered by each image.The number of X-ray detected clusters divided by the total number of clusters in each image is the fraction of clusters with X-ray sources.

Determining this fraction is not as straightforward as it seems:while the number of X-ray detected objects is well-understood,the number and identity of all true globular clusters in M31is not.The true num-ber of clusters in the central regions is particularly uncertain:globular clusters are dif?cult to detect against the bright,variable stellar back-ground,and the existing catalogs may be incomplete.We therefore computed two fractions:the fraction of con?rmed globular clusters detected as X-ray sources,and the fraction of all GC candidates de-tected.Since only a fraction of candidates are con?rmed,and not all cluster candidates are true clusters,these two values should bracket the true fraction of M31clusters with X-ray sources.

Figure9shows these fractions for each?eld as a function of the projected distance,R p,from the center of M31.The?gure also shows the fraction of Milky Way clusters with X-ray sources in four bins of

R p,where R p was computed for each cluster as if the Milky Way glob-

ular cluster system were viewed from the same inclination angle as the

M31GCS.Although in M31we have only four?elds and30detected

clusters,there is a clear decline in the fraction of M31clusters with X-

ray sources as R p increases,and a suggestion of the same effect in the

Milky Way.The Milky Way curve is bracketed by the two M31curves

(the dip at the second point is probably not signi?cant given the small

number of Galactic X-ray sources),suggesting that the pattern in the

two galaxies is similar.The decline in the number of X-ray sources

as R p increases can be understood if dynamical evolution drives the

creation of X-ray binaries,since dynamical evolution is expected to be

accelerated for clusters with orbits that bring them closer to the center

of a galaxy.

The overall fraction of clusters with X-ray sources is fairly similar

in the two galaxies.The Milky Way has12X-ray source clusters and

a total of147clusters,so～10%of clusters have X-ray sources.In

our M31?elds,the fraction of con?rmed clusters with X-ray sources

is25%,and the fraction of all cluster candidates with X-ray sources is

～7%.Again,to within our admittedly large uncertainties,the fraction of clusters with X-ray sources seems to be fairly similar in the two

galaxies.It is therefore tempting to view the combined Galactic and

M31globular clusters systems as a single population of clusters.In this

view,the clusters in M31can help us to learn more about conditions

in Galactic globular clusters,mainly by providing a larger population

of clusters to study.

5.2.Properties of Clusters with X-ray Sources

Do M31GCs with X-ray sources differ from those without?We

compared optical colors and apparent magnitudes,color excesses,

metallicities,radial velocities,and positions of the two populations

using data drawn from the Barmby et al.(2000)catalog.We also com-

pared estimates of the core radii,from Crampton et al.(1985),and

estimates of the clusters’ellipticities,from Staneva et al.(1996)and

D’Onofrio et al.(1994)(these estimates are from ground-based opti-

cal imaging and are not particularly precise;their major advantage is

that they are available for most of the clusters).A KS test was used

to determine whether the two populations were drawn from the same

distribution.The only signi?cant difference between the X-ray source

and non-X-ray-source clusters is in luminosity.The clusters with X-

ray sources are brighter than the non-X-ray clusters,at the99%con-

?dence level.The luminosity difference of the median values is0.55

magnitudes,or a?ux difference of a factor of1.7.

For20clusters(6with X-ray sources and14without),structural

parameters were also available from HST images(Barmby&Holland

2001).We compared the properties of the two groups and found only one signi?cant difference:the central surface brightness of the X-ray source clusters was much brighter(medianμ0,V=14.7)than that of the non-X-ray-source clusters(medianμ0,V=16.3).This result is only signi?cant at the92%level and is based on a small number of objects.However,it is consistent with the difference in optical lu-minosities found above,as studies of larger populations of Milky Way and M31clusters show that more luminous clusters tend to have higher central surface brightnesses(Djorgovski&Meylan1994;Barmby& Holland2001).In Figure10we show all the available structural prop-erties for M31and Milky Way clusters versus projected distance from the center of the galaxy.The?gure shows that the X-ray source clus-ters tend to be near the center of their parent galaxies,and as such tend to have high central surface brightnesses,small scale and half-light radii,and high concentrations.

We also compared the properties of M31clusters with X-ray sources

to those of Milky Way clusters with X-ray sources.The only possibly

signi?cant difference was in the luminosity:the M31X-ray clusters

were brighter in V than the Milky Way X-ray clusters.This is not

true of the GC populations in general—the overall globular cluster

luminosity functions are not signi?cantly different—so it could be a

clue to the M31GCs’higher X-ray luminosities.It would be interest-

ing to know whether the higher optical luminosities of the M31X-ray

16

F IG.9.—Fraction of GCs with bright X-ray sources as a function of projected separation,R p,from the galaxy center.

GCs translate into higher masses;unfortunately,mass determinations

from velocity dispersions are available only for a few M31GCs,and

only one of the X-ray sources.There are no clear correlations between

M31GC X-ray source luminosity and any of the cluster properties

mentioned above.

6.CONCLUSION:POSSIBLE EXPLANATIONS

6.1.Individual Bright M31GC Sources

Some individual X-ray sources in M31globular clusters are signif-

icantly more luminous than any individual X-ray source yet observed

in Galactic globular clusters.Bo375is an example.With changes in

?ux at the～50%level over16hours and at the100%level over times

ranging from months to years,it seems clear that a single component

must be contributing at least half of the X-ray energy emitted at typi-

cal times.This source would,by itself,approach the Eddington limit

for a1.4M⊙neutron star,and must be more than twice as X-ray lumi-

nous as the maximum L X measured for any Galactic globular cluster

X-ray source.We?nd similar variability effects in the500-day light

curves of2other highly luminous M31GC X-ray sources,Bo82and

Bo86.It may therefore be the case that the most luminous sources

we observe in M31GCs are either individual X-ray binaries(although

there is evidence in the ACIS-S image that Bo375may not be a point

source),or composites of a small number of independent X-ray bina-

ries.An alternative explanation might apply to some of the sources

not yet known to exhibit signi?cant short-term variation:that some of

the more luminous sources(L X>5×1037ergs s?1)are composed of

a fairly large number(～10)of typical Galactic globular cluster X-ray

binaries.Although not ruled out,such a large number of sources in

roughly1/4of M31’s globular clusters,with no composites at all yet

observed in Galactic globular clusters,seems extreme(see§6.2).

It is clear that the physical characteristics of at least those very

bright M31GC sources exhibiting signi?cant short-term variability

differ from those of Galactic GC sources.We have therefore analyzed

the spectra of the5brightest M31sources(the only M31GC sources

for which we have collected more than400counts)and compared

them,and also M31GC X-ray sources studied previously with Bep-

poSAX(Trinchieri et al.1999),with the spectra of Galactic sources.

The spectra are similar to those of Galactic GC sources,but2sources

exhibit somewhat harder power-law tails;one of these appears to make

transitions between a soft and a hard state.It is not possible to draw

conclusions about the physical nature of the sources from these crude

comparisons(which are nevertheless,the best presently possible).We

must therefore continue to carry out time variability and spectral stud-

ies that could possibly,in combination,tell us whether each source

is an accreting black hole or neutron star.High-spatial resolution ob-

servations with these sources on-axis,and spectra from longer obser-

vations with Chandra and BeppoSAX could play important roles,as

could XMM-Newton and HST observations.Progress along theoreti-

cal lines could also help to distinguish signatures of a relatively steady

black hole accretor from those of a neutron star accretor.

If it is an accreting black hole,the time signatures of the source in

Bo375are more characteristic of a persistent,rather than a transient

source.Although this would at?rst suggest a high-mass(M>5M⊙)

donor,such a donor is unlikely to be found in a globular cluster–even

if the cluster is relatively young and even if the rate of stellar intersac-

tions near the cluster core is high.Nevertheless,if a low-mass donor

is evolving away from the main sequence,a black hole accretor that

might otherwise be transient could be highly luminous over relatively

long times.

Below we construct a speci?c neutron star model for Bo375sug-

gested by the16hour time scale observed by ROSAT.This model may

or may not describe the actual physics of Bo375,but it is consis-

tent with the data and could apply to other bright GC sources in the

youngest clusters of M31and other galaxies.

6.2.A Model for Bo375

The spectral and timing studies we have been able to carry out so

far have not provided promising clues as to the nature of this X-ray

source(or sources).It is intriguing,however,that ROSAT observations

17

F I

G .10.—Structural parameters versus projected distance R p from the galaxy center for M31and Milky Way globular clusters.Core-collapsed Milky Way GCs are squares,non-core-collapsed Milky Way GCs are triangles,and M31GCs are hexagons.(De?nitive detection of core-collapse in M31GCs is not possible with existing data).Filled symbols represent clusters with bright X-ray sources;open symbols represent all other clusters.Globular cluster surface brightness distributions are described by King models with three parameters:r 0,the scale radius (sometimes mis-called the core radius),c ,the concentration (c =log(r t /r 0),where r t is the tidal radius),and μ0,V ,the central surface brightness.r h ,the half-light radius,is another commonly-used measure of cluster size which combines c and r 0.Data for the Milky Way clusters is from the Harris (1996)catalog;data for the M31clusters is from Barmby &Holland (2001),which contains a detailed comparison of M31and Milky Way clusters’structural properties.

found what appeared to be systematic,possibly periodic,variations on a time scale of ～16hours.If these variations are associated with an orbital period,this would suggest that mass transfer is occurring on the thermal-time-scale of a slightly evolved Roche-lobe ?lling star.

6.2.1.Thermal Time Scale Mass Transfer

Thermal-time-scale mass transfer is driven by the reaction of a Roche-lobe-?lling donor star to mass loss (van den Heuvel et al.1992;Kalogera &Webbink 1996;Di Stefano &Nelson 1996;King et al.2001;King &Begelman 1999).Consider a donor star which would,were it living in isolation,have an equilibrium radius R eq determined by its total mass and state of evolution.If this star is in a close binary and is ?lling its Roche lobe,in a situation in which R L is consistently somewhat smaller than R eq ,then the drive of the star to achieve equi-librium causes it to lose mass through the L1point at a relatively rapid rate.In fact,if the ratio of the donor mass to the accretor mass is too large,or if the donor is evolved enough to be fully convective,the mass transfer process can become dynamically unstable,leading to the for-mation of a common envelope.If,however,a dynamical instability is avoided,mass transfer is driven on a time scale closely related to the thermal time scale of the donor.

In general,the two assumptions of a Roche-lobe ?lling donor and angular momentum conservation lead to an analytic expression for ˙m ,the rate at which the donor loses mass.This expression can be written generically as

˙m =

N R eq

1

18

by a Henyey-like calculation.The favored values for the calculations we present below are taken from work by Nelson(1995).For more de-tails about this type of mass transfer,see Di Stefano&Nelson(1996) and references therein.

6.2.2.System Properties

When the accretor is a neutron star,only a narrow range of donor masses and states of evolution(as speci?ed by the helium core mass) will permit dynamically stable mass transfer driven on the thermal time scale of the donor.In Figure10we have shown the range of system parameters for such systems at that point in their evolution at which P orb is16hours and the accretion rate onto a neutron star companion has just increased to10?8M⊙.Donor masses range from1.1?1.6M⊙and donor core masses are near0.11M⊙.These systems are similar to the“intermediate-mass binaries”studied by Davies&Hansen(1998) in signi?cant young GCs.

6.2.3.Evolution

Although we don’t know that the16-hour time variability of Bo375 is related to an orbital time scale,it is reasonable to entertain this pos-sibility.To this end we computed the evolution of tens of thousands of systems.Shown in Figure11are the results of some typical evolutions of binaries that would have accretion energies greater than1038ergs s?1 during a time interval in which their orbital periods are16hours.Note that during the early parts of the evolution,the donor’s radius(which is governed by its total mass is also in?uenced by its core mass),and the orbital period can decrease.

6.2.4.Viability in a Globular Cluster Environment

This sort of scenario has not been considered for neutron stars in GCs,because the required mass of the donor star is larger than the mass of stars at the turn-off of typical Galactic GCs(Di Stefano& Davies1996have considered such a scenario for white dwarfs;see Hertz,Grindlay,&Bailyn1993;Verbunt et al.1994,1995).There are two sets of circumstances,however,that alone or in combination can provide a pool of massive donor stars.The?rst and simplest is a younger cluster age.Although most Galactic GCs seem to have been formed between12and15Gyr ago,other galaxies may have experi-enced several distinct epochs of globular cluster formation.This seems to have been the case in the Magellanic Clouds(see,e.g.,Da Costa, Mould,&Crawford,1985),and is also expected in galaxies that have experienced interactions with neighboring galaxies.We do not know if M31contains GCs formed during different epochs,but Barmby, Huchra,&Brodie(2001)have suggested that the difference in optical luminosity between the inner and outer GCs in M31can be explained if the brighter clusters are～55%younger than the fainter clusters. Young clusters formed7?9Gyr ago could harbor slightly evolved stars that would?t the criteria shown in Figure10for a thermal-time-scale mass transfer system with a16hour period.

In addition,a relatively high probability of interactions enhances the probability of?nding a massive star in a close orbit with a neutron star.If,for example,interactions among massive stars in the core re-gion have led to stellar mergers,thermal-time-scale mass transfer onto

a neutron star could be expected occur in GCs.

6.2.5.Tests

One test of the applicability of our model to individual bright sources in M31would be the discovery of time～1day variations among the M31GC sources(or in other galaxy’s GCs)that can be reasonably linked to an orbital period.Another test can be applied to galaxies with GC systems that house highly luminous sources that are candidates for our model:are the relative numbers of systems of dif-ferent luminosities consistent with the lifetimes of the corresponding phases of binary evolution?We?nd,for example,that the epoch dur-ing which the luminosity remains above1038ergs s?1is approximately 107years,roughlyτKH for the donor.The lifetime of the accretion luminosities above1037ergs s?1are～10times longer.This roughly matches the statistics of the M31GC sources.Finally,as we probe the globular cluster systems of more distant galaxies,we can search for correlations between the X-ray luminosities of GCs and the ages of GCs.While no individual test is likely to be de?nitive,a combination of them could provide support for,or else falsity,the model.

6.3.Other M31Globular Clusters

This paper started as a description of an interesting X-ray luminous globular cluster,Bo375,which happened to be in the?eld of view of a Chandra census of M31.Its high luminosity,together with indica-tions that the source is not point-like,attracted our attention to this cluster.The fact that others of the most luminous sources studied in the census are also associated with globular clusters led us to extend our investigation and to?nd that the high-end of the the GC X-ray source luminosity function has a higher peak luminosity and a larger fraction of all sources populating the region with L X>1037ergs s?1. The fundamental issue we address in this section,is why M31’s glob-ular clusters should be more likely than those of our own Galaxy to house brighter X-ray sources and multiple X-ray sources.We?nd that three effects are likely to be at work.

6.3.1.Possible Explanations:https://www.sodocs.net/doc/f45904412.html,rge Population of Clusters

Let us entertain the hypothesis that the Milky Way and Andromeda globular clusters are members of a single distribution of clusters.In this case,the total population of clusters could be～550.We certainly wouldn’t expect that every possible cluster phenomenon could be dis-covered in the arbitrary subset of150that we happen to?nd in our own Galaxy.If,e.g.,black hole binaries are only1/20as likely to form and remain in clusters as are neutron star binaries,we would have a small chance of observing one among the14MW GCs with X-ray sources, but would have an improved chance of discovering one in the～50 X-ray active GCs in M31.Unfortunately,however,we have no a pri-ori estimates of the probability of events(such as the formation of a black-hole binary)that(a)have never been observed,and that(b)are not readily amenable to reliable?rst-principles predictions.Thus,all that can be said is that we should perhaps not be too surprised if some of M31’s GCs do contain actively accreting black holes,or unusually massive(e.g,2?3M⊙)accreting neutron stars,or even unusually mas-sive donor stars.

There is,however,one yet-to-be-observed GC situation,for which the probability can be estimated.This is the situation in which a cluster houses more than one bright X-ray binary.If p represents the probabil-ity of?nding an X-ray source in a GC,Poisson statistics predict that, for every GC with a single X-ray source,there should be p/2clus-ters with2sources and p2/6clusters with3sources.If p～0.1?0.2, we would predict that3?5GC X-ray sources in M31should be com-posites of2independent sources,while fewer than1is likely to be composed of3independent sources.

One can also attack this question of the probability of multiplicity from the perspective of the probability of the2?,3?,and4?body pro-cesses that produce X-ray binaries.What is the probability that two interactions will produce2independent X-ray sources that are active at the same time?Such a question certainly can be well posed and answered subject to input assumptions about the lifetimes of X-ray bi-naries,Since,however,current estimates of the lifetime of X-ray activ-ity vary by1?2orders of magnitude,the most reliable answer comes from the phenomenology that allows us to estimate p.It is important to note,however,that if a subset of clusters have different physical char-acteristics,the true probability of observing multiple X-ray sources in these GCs could be different,

6.3.2.Possible Explanations:II.More Highly Evolved

Clusters

Although there are striking similarities between the MW and An-dromeda galaxies,they are not identical.In fact there are differences that are likely to lead to more or(“enhanced”)accelerated evolution of GCs close to the center of M31than of clusters close to to the center of

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G .11.—Each dot corresponds to a physical system with an orbital period of 16hours,and an accretion luminosity above 1038erg s ?1.

the MW.According to van den Bergh (2000),the nuclear mass of M31is almost 30times larger than the nuclear mass of the MW (7×107M ⊙vs 2.5×106M ⊙).The bulge dispersions are 155km/s and 130km/s,respectively,while the rotational velocities are,respectively,260km/s vs 220km/s.All of these differences indicate that GCs close to the center of M31are likely to evolve more quickly than clusters close to the center of our Galaxy (see,e.g.,Gnedin,Lee,&Ostriker 1999,and references therein).Since cluster evolution leads to smaller and denser cores,at least until the onset of core collapse,the conditions that lead to the formation of X-ray binaries may also be enhanced,leading to more X-ray binaries in M31GCs.Certainly the fact that there are more X-ray luminous clusters closer to the centers of both M31and the MW speaks in favor of the role of accelerated evolution.Barmby,Huchra &Brodie (2001)?nd an apparent dearth of low-mass clusters near the center of M31,consistent with theoretical calculations of ac-celerated evolution;however,they ?nd that the width of the optical luminosity function is not consistent with the same calculations.

There is an argument that may not favor enhanced accelerated evo-lution as the primary reason for the brighter X-ray luminosities of M31GCs.This is that,so far,the fraction of M31globular clusters in each region of the galaxy seem comparable to the fraction observed at sim-ilar values of R p for the MW.As we have pointed out,these results are subject to signi?cant uncertainties.But,if it is true that the frac-tion of GCs with X-ray sources is indeed comparable for comparable values of R p ,this would appear to limit the role of enhanced acceler-ated evolution.It could,however,still be invoked to explain higher cluster X-ray luminosities in M31through the formation of more or brighter binaries if,e.g.,the time scale for X-ray emission is only a short fraction of the cluster’s orbital period.

In summary,it is dif?cult to quantify the role of accelerated evo-lution due to interaction of M31’s GCs with the rest of the galaxy.Nevertheless,it is likely that it does play a somewhat different role in M31than in the MW,simply because of the differences in mass and mass distribution in the 2galaxies.If,therefore,we wish to view the two systems of globular clusters as a single larger system of some

400?550clusters,we must invoke the proviso that none of the Galac-tic clusters experience tidal and disk interactions as extreme as those experienced by clusters which pass close to the center of M31.That is,if we were to map Galactic clusters onto M31,in such a way that their interactions with M31would mimic the conditions each actually expe-riences due to the Milky Way,the Galactic clusters would generally be placed farther from the center of M31than their actual distance from the center of the Galaxy.Thus,M31may be expected to contain not only globular clusters with properties that are similar to those found in our Galaxy,but also a sub-population whose evolution is proceeding at a more rapid pace due to interactions with M31;these more rapidly evolving clusters are most likely to be found near the center of M31.Note that if enhanced accelerated evolution to reponsible for the more luminous GC X-ray sources in M31,then M31GCs with bright X-ray sources should have different structure parameters.HST observations could therefore help to determine the role of enhanced accelerated evo-lution.

6.3.3.Possible Explanations:III.Younger Clusters

We have found that the M31GCs with X-ray sources tend to be optically brighter than clusters without X-ray sources.Barmby et al.(2001)suggested that a younger age might account for the higher av-erage luminosity of the metal-rich M31GCs compared to the metal-poor clusters.Metallicity is not strongly correlation with the proba-bility that an M31GC has an X-ray source;however,it is interesting to consider the possibility that the X-ray source clusters are optically brighter because they are younger.If this is true,the X-ray source clus-ters would have a higher turn-off mass (1.1–1.2M ⊙)than older clus-ters,for which the turnoff is 0.8M ⊙.It is much more likely to ?nd a donor with high-enough mass for thermal-time-scale mass transfer to occur in a GC with a turnoff at ～1.1M ⊙.This can be easily under-stood by noting that all of the low-probability interactions that could produce such a binary in an old clusters are supplemented by a wealth of additional interactions involving stars of relatively high mass.Fur-thermore there is a clear prediction that thermal mass transfer is much

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F IG.12.—Evolution of a typical system which has accretion luminosity above1038erg s?1during a time when its orbital period is16hours.β=1:In this case,the neutron star accretes all of the incident matter.If,however,β=1would produce super-Eddington accretion,the value ofβis calculated in an internally-consistent way(see Di Stefano2001).Note that for non-zeroβ,the mass of the neutron star can increase.β=0:the mass of the neutron star is held constant.In both cases the middle curve was computed using the values for the thermal time-scale readjustment of the donor computed by Nelson(1995).The upper and lower curves tested the effects of altering these values(which are uncertain)by about an order of magnitude.

more likely in younger clusters.Calculations are underway to quantify

this effect.

6.4.Conclusions

M31globular clusters could have turned out to have X-ray proper-

ties almost exactly like those of the Milky Way.In this case,studies

of M31would have told us more about the processes that go on in

our own Galaxy,simply because their larger numbers provide a big-

ger arena for the relevant interactions to occur.M31globular clusters

could have turned out to have X-ray properties very different from

those of the Milky Way.In this case they might have provided a gate-

way to our understanding of GCs in external galaxies.

The population of M31GCs did turn out to be include clusters that

appear to have similar X-ray properties to those of the MW,as well as

a signi?cant subset that have different X-ray properties.Perhaps this

is the best of both worlds,because we can now hope to learn about

processes occurring in our own GCs,and also about processes that do

not occur here or occur only with very low probability.

For example,we might expect to?nd highly-luminous thermal-

time-scale mass transfer systems in galaxies with populations of young

clusters,and none such in galaxies such as our own,with only old

populations of stars in GCs.Thus,the relevance of the thermal-

time-scale model we have introduced,can be tested by determining

whether galaxies thought to include more recently formed GCs have

more highly luminous GC X-ray sources.Similarly,the importance of

interactions with the host galaxy can be tested by comparing GC X-

ray sources in galaxies that have more massive bulges with GC X-ray

sources in galaxies with less massive bulges.

In short,Chandra’s investigation of the M31GC system has pro-

vided puzzles that suggest many lines of investigation for the further

study of M31’s GCs,GCs in external galaxies,and theoretical work on

binary formation and evolution in globular clusters.

We gratefully acknowledge thoughful input from Anil Dosaj,

Lars Hernquist,Margarita Karovska,Vicky Kalogera,Christopher

Kochanek,Lucas Macri,Jeff McClintock,and Andrea Prestwich.This

work was supported in part by NASA under GO1-2091X;A.K.H.K.is

supported by a Croucher Fellowship.

REFERENCES

Ajhar,E.,et al.1996,AJ,111,1110

Barmby,P.2001,PhD thesis,Harvard University

Barmby,P.,&Huchra,J.P.2001,AJ,in press(astro-ph/0107401)

Barmby,P.,&Holland2001,AJ,submitted

Barmby,P.,Huchra,J.P.&Brodie,J.P.2001,AJ,121,1482

Barmby,P.,Huchra,J.P.,Brodie,J.P.,Forbes,D.A.,Schroder,L.L.&Grillmair,

C.J2000,AJ,119,727

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指令语句表示一种与计算机汇编语言相类似的助记符编程方式，但比汇编语言易懂易学。一条指令语句是由步序、指令语和作用器件编号三部分组成。 3．控制系统流程图编程图 控制系统流程图是一种较新的编程方法。它是用像控制系统流程图一样的功能图表达一个控制过程，目前国际电工协会（IEC）正在实施发展这种新式的编程标准。 二、基本指令简介 基本指令如表所示 取指令 LD I、Q、M、SM、T、C、V、S、L 常开接点逻辑运算起始 取反指令 LDN I、Q、M、SM、T、C、V、S、L 常闭接点逻辑运算起始 线圈驱动指令

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射线数字成像专业书籍《实时射线成像检测》王建华李树轩编著 目录： 前言 第1章射线成像的物理基础 1.1物质构成 1.1.1元素 1.1.2原子 1.2同位素 1.2.1核素 1.2.2同位素 1.2.3核素分类 1.2.4原子能级 1.3原子核结构 1.3.1核力 1.3.2核稳定性 1.3.3放射性衰变

1.4射线种类和性质 1.4.1射线分类 1.4.2X射线和γ射线的性质 1.4.3X射线和γ射线的不同点 1.4.4射线胶片照相中使用的射线 1.5射线的产生 1.5.1X射线的产生 1.5.2γ射线的产生 1.5.3高能X射线 1.5.4中子射线 1.6射线与物质的相互作用 1.6.1光电效应 1.6.2康普顿效应 1.6.3电子对效应 1.6.4瑞利散射 1.6.5各种效应相互作用发生相对的几率 1.7射线的衰减规律 1.7.1吸收、散射与衰减 1.7.2射线的色和束 1.7.3单色窄束射线的衰减规律 1.7.4宽束、多色射线的衰减规律（包括连续X射线）

测试题（是非题） 第2章实时成像 2.1实时成像的基础 2.1.1简述 2.1.2实时成像的原理 2.1.3射线成像的特点 2.1.4射线成像的应用 2.1.5实时成像局限性 2.2实时成像技术 2.2.1实时成像系统 2.2.2射线成像设备 2.2.3成像系统的构成 2.2.4成像转换装置（成像器） 2.3射线辐射转换器 2.3.1X射线荧光检验屏 2.3.2X射线图像增强器 2.4射线数字化成像技术 2.4.1计算机射线照相技术 2.4.2线阵列扫描成像技术 2.4.3光纤CCD射线实时成像检测系统（简称光纤CCD系统） 2.4.4数字平板直接成像技术

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锂硫电池的研究现状 近年来，随着不可再生资源的逐渐减少，清洁能源的利用逐渐得到重视，而电池作为储能装置也受到越来越多的考验。锂硫电池与传统的锂离子电池相比，优势主要在于硫的高比容量，单质硫的理论比容量为1600mAh/g ，理论比能量2600Wh/kg。并且硫是一种廉价且无毒的原材料。而与此同时，硫作为锂电池的正极材料也存在着诸多问题[1]： 1、单质硫以及最终放电产物都是绝缘的，如果与正极中掺入的导电物质结合不好，就会导致活性物质不能参与反应而失效； 2、单质硫在反应过程中会生成长链的聚硫化物离子S n2-，这种离子容易溶解在电解液中，并与锂负极反应，产生“穿梭效应”，引起自放电并使库伦效率降低； 3、在每次放电过程结束之后，都会有一些Li2S2/Li2S沉淀在正极上，并且这些不溶物随着循环次数的增加，在正极表面发生团聚，并且正极结构也会发生变化，导致这部分活性物质不能参与电化学反应而失效，并且使电池的内阻增加； 4、硫正极随充放电的进行会产生约22%的体积变化，从而导致电池物理结构破坏而失效。 针对硫作为正极材料的种种弊端，研究者们分别采用了多种方法予以解决，其中将硫与碳材料复合的研究较多。针对几种典型方法，分别举例介绍如下：一、石墨烯-硫复合材料 Wang等人采用石墨烯包覆硫颗粒的方法制作复合材料电极[2]。如图1所示，他们首先采用化学方法制备了硫单质，并利用一种特殊的表面活性剂Triton X-100在硫颗粒的表面修饰了一些PEG高分子，然后再用导电炭黑和石墨烯的分散液对硫颗粒进行包覆。这种方法的优点在于：首先，石墨烯和导电炭黑具有优异的导电性能，可以克服硫以及硫反应产物绝缘的问题；第二，导电炭黑、石墨烯和PEG高分子对硫颗粒进行了包覆，可以解决硫在电解液中溶出的问题；第三，PEG高分子具有一定的弹性，可以在一定程度上缓解体积变化带来的影响。 二、碳纳米管-硫复合材料 Zheng等人用AAO做模板制备了碳纳米管阵列[3]，随后将硫加热使其浸入到碳纳米管中间，然后将AAO模板去掉，得到碳纳米管-硫复合材料，如图2所示。这种方法的优点在于碳纳米管的比表面积大，有利于硫化锂的沉积。并且长径比较大，可以较好地将硫限制在管内，防止其溶解在电解液中。碳纳米管的导电性好管壁又很薄，有利于离子导通和电子传输。同时，因为制备过程中先沉积硫，后去除模板，这样有利于使硫沉积到碳管内，减少硫在管外的残留，从而防止这部分硫的溶解。

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指令设定一览表 惯例 x：立即数m：数据存储器地址A：累加器 i：0~7 号位 addr：程序存储器地址 Rev 1.00 66 2011-04-13

注： 1. 对跳转指令而言，如果比较的结果牵涉到跳转即需2个周期，如果没有跳转发生，则只需一个周期即可。 2. 任何指令若要改变PCL的内容将需要2个周期来执行。 3. 对于“CLR WDT1”和“CLR WDT2”指令而言，TO和PDF标志位也许会受执行结果影响，“CLR WDT1” 和“CLR WDT2”被连续执行后，TO和PDF标志位会被清零，除此外TO和PDF标志位保持不变。 Rev 1.00 67 2011-04-13

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C:\WINNT\Profiles\Administrator>vxdisk list -v Name MediaName Diskgroup DiskStyle Size(MB) FreeSpace(MB) Status Port Target Channel LUN Harddisk0 RAW 502 7 Uninitialized 0 0 0 0 Harddisk1 Disk1 DataDisk MBR 140270 0 Imported 2 0 0 0 Harddisk2 Disk2 DataDisk MBR 140270 140270 Imported 2 4 0 0 Harddisk3 BasicGroup MBR 70135 7 Uninitialized 2 7 0 0 检测出target id. vxdisk list Name MediaName Diskgroup DiskStyle Size(MB) FreeSpace(MB) Status Harddisk0 BasicGroup MBR 502 7 Uninitialized Harddisk1 Disk1 DataDisk RAW 140270 0 Imported Harddisk2 Disk2 DataDisk RAW 140270 0 Imported Harddisk3 BasicGroup MBR 70135 7 Uninitialized C:\>vxdisk diskinfo Harddisk1 Disk information Device Name : Harddisk1 Media Name : Disk1 Disk Group : DataDisk Disk Style : RAW Length : 147084424704 FreeSpace : 0 BusType : 4 Port : 2 Target : 0 Channel : 0 LUN : 0 Signature : 0 Status : Imported Comment : Subdisks : Disk1-01 Disk1-02 C:\>vxdisk diskinfo Harddisk1 Disk information Device Name : Harddisk1 Media Name : Disk1 Disk Group : DataDisk Disk Style : RAW Length : 147084424704 FreeSpace : 0 BusType : 4 Port : 2 Target : 0 Channel : 0 LUN : 0 Signature : 0 Status : Imported

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术，检测周期长、效率低下。“十二五”期间，将有更多的油气管道建设工程相继启动，如何将一种可靠的、快速的、“绿色”的射线数字检测技术应用于工程建设中，以替代传统射线胶片检测技术已成为目前管道焊缝射线检测领域亟需解决的问题。 2 国内外管道焊缝数字化检测的现状 2.1 几种主要的射线数字检测技术 1）CCD型射线成像（影像增强器） 2）光激励磷光体型射线成像（CR） 3）线阵探测器（LDA）成像系统 4）平板探测器（FPD）成像系统 几种技术各有特点，目前适用于管道工程检测的是CR 和FPD，但CR不能实时出具检测结果，且操作环节较繁琐、成本较高，因此平板探测器成像系统成为射线数字检测的主要发展方向。 2.2 国内研发情况 国内目前从事管道焊缝射线数字化检测系统研发的机构主要有几家射线仪器公司，但其产品主要用于钢管生产厂的螺旋焊缝检测。通过实践应用比较，研究应用电子学研究所研发的基于平板探测器的管道焊接射线数字化检测与评估系统已能够满足管道工程检测需要，并通过了科技成果鉴

(完整版)全固态锂电池技术的研究进展与展望

全固态锂电池技术的研究进展与展望 周俊飞 （衢州学院化学与材料工程学院浙江衢州324000） 摘要：现有电化学储能锂离子电池系统采用液体电解质，易泄露、易腐蚀、服役寿命短，具有安全隐患。薄膜型 全固态锂电池、大容量聚合物全固态锂电池和大容量无机全固态锂电池是一类以非可燃性固体电解质取代传统锂离 子电池中液态电解质，锂离子通过在正负极间嵌入-脱出并与电子发生电荷交换后实现电能与化学能转换的新型高 安全性锂二次电池。作者综述了各种全固态锂电池的研究和开发现状，包括固态锂电池的构造、工作原理和性能特 征，锂离子固体电解质材料与电极/电解质界面调控，固态整电池技术等方面，提出并详细分析了该技术面临的主要 科学与技术问题，最后指出了全固态锂电池技术未来的发展趋势。 关键词：储能；全固态锂离子电池；固体电解质；界面调控 1 全固态锂电池概述 全固态锂二次电池，简称为全固态锂电池，即电池各单元，包括正负极、电解质全部采用固态材料的锂二次电池，是从20 世纪50 年代开始发展起来的[10-12]。全固态锂电池在构造上比传统锂离子电池要简单，固体电解质除了传导锂离子，也充当了隔膜的角色，如图 2 所示，所以，在全固态锂电池中，电解液、电解质盐、隔膜与黏接剂聚偏氟乙烯等都不需要使用，大大简化了电池的构建步骤。全固态锂电池的工作原理与液态电解质锂离子电池的原理是相通的，充电时正极中的锂离子从活性物质的晶格中脱嵌，通过固体电解质向负极迁移，电子通过外电路向负极迁移，两者在负极处复合成锂原子、合金化或嵌入到负极材料中。放电过程与充电过程恰好相反，此时电子通过外电路驱动电子器件。目前，对于全固态锂二次电池的研究，按电解区分主要包括两大类[13]：一类是以有机聚合物电解质组成的锂离子电池，也称为聚合物全固态锂电池；另一类是以无机固体电解质组成的锂离子电池，又称为无机全固态锂电池，其比较见表1。通过表1 的比较可以清楚地看到，聚合物全固态锂电池的优点是安全性高、能够制备成各种形状、通过卷对卷的方式制备相对容易，但是，该类电池作为大容量化学电源进入储能领域仍有一段距离，主要存在的问题包括电解质和电极的界面不稳定、高分子固体电解质容易结晶、适用温度范围窄以及力学性能有提升空间；以上问题将导致大容量电池在使用过程中因为局部温度升高、界面处化学反应面使聚合物电解质开貌发生变化，进而增大界面电阻甚至导致断路。同时，具有隔膜作用的电解质层的力学性能的下降将引起电池内部发生短路，从面使电池失效[14-15]。无机固体电解质材料具有机械强度高，不含易燃、易挥发成分，不存在漏夜，抗温度性能好等特点；同时，无机材料处理容易实现大规模制备以满足大尺寸电池的需要，还可以制备成薄膜，易于将锂电池小型化，而且由无机材料组装的薄膜无机固体电解质锂电池具有超长的储存寿命和循环性能，是各类微型电子产品电源的最佳选择[10]。采用有机电解液的传统锂离子电池，因过度充电、内部短路等异常时电解液发热，有自燃甚至爆炸的危险（图3）。从图 3 可以清楚地看到，当电池因为受热或短路情况下导致温度升高后，传统的锰酸锂或钴酸锂液体电解质锂离子电池存在膨胀起火的危险，而基于纯无机材料的全固态锂电池未发生此类事故。这体现了无机全固态锂电池在安全性方面的独特优势。以固体电解质替代有机液体电解液的全固态锂电池，在解决传统锂离子电池能量密度偏低和使用寿命偏短这两个关键问题的同时，有望彻底解决电池的安全性问题，符合未来大容量新型化学储能技术发展的方向。正是被全固态锂电池作为电源所表现出来的优点所吸引，近年来国际上对全固态锂电池的开发和研究逐渐开始活跃[10-12] 2 全固态锂电池储能应用研究进展 在社会发展需求和潜在市场需求的推动下，基于新概念、新材料和新技术的化学储能新体系不断涌现，化学储能技术正向安全可靠、长寿命、大规模、低成本、无污染的方向发展。目前已开发的化学储能装置，包括各种二次电池（如镍氢电池、锂离子电池等）、超级电容器、可再生燃料电池（RFC：电解水制氢-储氢-燃料电池发电）、钠硫电池、液流储能电池等。综合各种因素，考虑用于大规模化学储能的主要是锂二次电池、钠硫电池及液流电池，而其中大容量储能用锂二次电池更具推广前景。。 全固态锂电池、锂硫电池、锂空气电池或锂金属电池等后锂离子充电电池的先导性研究在世界各地积极地进行着，计划在2020 年前后开始商业推广。在众多后锂离子充电电池中，包括日本丰田汽车、韩国三星电子和德国KOLIBRI 电池公司对全固态锂电池都表现出特别的兴趣。图 4 为未来二十年大容量锂电池的发展路径，从图 4 可以看出，全固态电

魔兽世界命令大全

/help 列出常用指令帮助 /assist [名字] 协助你当前所选择的目标，或者指定的目标 /cast spell 施放指定的法术，可以包含法术的等级。比如： "/cast Slow Fall", "/cast Polymorph(Rank 2)" /afk [文字] 开启AFK模式显示你要离开一会儿，再输一次/afk关闭AFK模式。 /combatlog 导出你的战斗信息到(wow目录)LogsPlayerCombatLog.txt 文件里。 /dnd [文字] 开启DND模式表示“请勿打扰”，再输一次/dnd关闭DND模式。 /duel [名字] 要求与你锁定的目标决斗，或者要求与指定的目标决斗。 /yield (/forfeit) 在决斗时投降。 /emote 文字 (/em, /me) 表示接下来的文字是动作。 /exit 退出游戏。 /follow (/f) 自动跟随当前目标。 /ignore 名字忽略目标玩家。 /inspect (/ins) 查看目标玩家的装备。 /logout (/camp) 坐下并且登出。 /macro 打开宏设置界面。 /macrohelp 给出关于设置宏的帮助。 /played 显示你游戏人物的在线时间。 /pvp 在接下来的5分钟内开启PVP模式。 /raid 文字 (/r) 在RAID频道里说话。 /random 数字 [数字2] (/rnd, /rand) 扔出一个从1到某个数字范围内的随机数字，或者是两个数字范围之间的随机数字。 /remfriend 名字 (/removefriend) 把一个好友从你的好友列表里去掉。

三星手机测试指令大全

只要不是CDMA的你就按*#06# 记住手机屏幕上的号码！！ 然后你关机取下电池对照后面的号码！ 如果是行货那肯定是回和他一样的， 如果不是行货就会不相同或者不显示 摩托罗拉 （1）产地及生产日期的查询：摩托罗拉手机背后都有一个MSN机械序号，共10位。它代表着“机型代码，厂家代码，生产年份，生产月份和产品系列号”。察看方法是关机，把后盖和电池拿开，在机身背后的条形码下面有一串号码，其中中间的十位就是MSN码，前三位为型号代码，第四码为生产厂家码，每五位为生产年份码，每六位为生产月份码，后四位为序列号。 （2）软件和功能：水货机无移动QQ，无法在机上查版本。港行只有繁体字输入。欧版机，如果没刷中文包，那就是纯粹外文机 MSN码---机械序号： 1。如何查看：关机，把后盖和电池拿开，在机身背后的条形码下面有：如：MC3-41E11 C836DD3P4R 350904805489928 的一串号码。其中“C836DD3P4R”就是MSN码，共十位。 2.代表的意思如下：前三位为型号代码;第四位为生产厂家码，第五，第六位为生产日期码（前面为年份，后面为月份）;后四位为序列号. （1）生产厂家码(第四码)：6-天津3-杭州2-美国R-德国G-美国5-杭州东信W-是新加坡（2）生产年份(第五码)：X-1997年Y-1998年Z-1999年H-2000年B-2001年C-2002年D-2003年E-2004 F-2005（3）生产月份(第六码)：A-B --1月C-D --2月E-F --3月G-H --4月J-K --5月L-M --6月N-P --7月Q-R --8月S-T --9月U-V --10月W-X --11月Y-Z --12月（注：前一个代表上半月，后一个代表下半月） 三. 水货与行货的区别 1.大陆行货,带有移动QQ 功能.可机上查版本. 2. 港行:有简体及繁体界面选择,但只能输入繁体字.无移动QQ.无法在机上查版本. 3. 新加坡版: 简体界面,简体输入.无移动QQ. 可机上查版本.其它信息里的语言列表是002 4. 4. 欧版,如果没刷中文包,那纯粹外文机. 刷了什么版本就跟什么版本的功能一样.不过键盘无笔划印刷。 电池： 摩托罗拉原装电池选购指南

课堂指令语

1.Let’s get ready for class. 准备上课。 2.Class begins.上课。 3.Open your books, please.请翻开书。 4.please turn to Page 12.请翻开书到12页。 5.Please take out your notebooks/exercise books.请拿出笔记本/练习本。 6.No more talking, please.请安静。 7.Attention, please.请注意。 8.Are you ready?准备好了吗？ 9.Who can answer this question?谁能回答这个问题？ 10.Raise your hands, please. 请举手。 11.Hands down.把手放下。 12.Repeat after me/Follow me.跟我读。 13.Are you clear ?明白了吗？ https://www.sodocs.net/doc/f45904412.html,e up to the front, please.请到前面来。 15.Go back to your seat, please.请回座位。 https://www.sodocs.net/doc/f45904412.html,e on. You can do it.来吧！你能做到的。 https://www.sodocs.net/doc/f45904412.html,e on, you’re almost there.来吧！你快（做/答）对了。 18.I’ll give you a clue (hint).我给你一些提示。 19.You can do it this way.你可以这样来做。 20.Let’s play a game.让我们玩个游戏。 21.Are you tired? Let’s take a break.累了吗？休息一下。 22.Do you have any questions?你们有问题吗？ 23.Be brave / active, please.请勇敢/主动些。 24.I beg your pardon?对不起，能再说一遍吗？ 25.Put up your hands if you have any questions.如果有问题请举手。 26.Take it easy.请放心/别紧张。 27.Let’s have a dictation.让我们来听写。 28.Let me see.让我看看/想想。 29.Listen to me, please.请听我说。 30.Look at the blackboard/screen, please.请看黑板/屏幕。 31.All eyes on me, please.请都看着我。 32.Can you solve this problem?能做出这道题吗？

英语课堂常用教学指令语的分类及使用

英语课堂常用教学指令语的分类及使用 发表时间：2012-07-06T09:45:43.427Z 来源：《教育学文摘》2012年8月总第61期供稿作者：◆周琪凤 [导读] 例如，T：All right？OK？Does everyone understand“polite”now？ ◆周琪凤山东省淄博市临淄区边河中学255400 在英语课堂上，教师的教学语言是学生输入和输出语言信息的重要渠道，是师生运用所学语言进行沟通的主环境。可以说，真实交际、自然习得是新课改中英语教师课堂语言行为的最高境界，是值得每一位教师关注的问题。 那么，要想科学利用英语教学语言的输入功能，在课堂教学过程中促成学生在完成学习任务的过程中自然地习得语言，我们教师必须熟知英语课堂教学语言的特征和功能类别，懂得如何优化教学语言并富有成效地组织课堂教学。 一、教学指令的分类 课堂教学指令的作用是引发、启动或制止学生的学习行为，组织和维系课堂教学活动。课堂指令包括三种：学生行为引发指令、课堂纪律控制指令和教学活动实施指令。 二、教学指令在课堂中的使用 1.教学指令在提问中的使用 提问是最典型的教学语言，它是促进语言学习的直接教学手段，视角不同，对提问的分类也不尽相同。英语教师的课堂教学提问包括五种类型，即“Yes/No形式提问、Or形式提问、Wh形式提问、引导式提问和形声式提问”。 Yes/No形式提问、Or形式提问和Wh形式提问是最常见的问题呈现形式。引导式提问是由教师提示前半部分信息，由学生配合并补全后半部分信息。例如，T：Jame is not at school today because….S:he is ill. 形声式提问，即教师通过重复话语来确认学生是否准确理解了教学要点。例如，T：All right？OK？Does everyone understand“polite”now？ 另外还有人把任何有询问形式或询问功能的教学提示都称为提问，具体分为“课堂程序性提问、课文理解性提问和现实情境性提问”。 研究者把组织学习活动功能的教学实施指令（如：“Ready？Go！”“One,two,start.Read after me.”“Let’s play a game.Let’s read it together,OK？Would you please read them again？”），“了解学生对学习任务的准备和完成情况”、具有检查课堂教学进度功能的简短询问（“Ready？”“Finished？”“One more minute？”“Understand？”“Clear？”“Got it？”），以及“用于学生回答问题后，根据学生回答问题的具体情况”具有“向全班、部分或学生个体征求意见或进行评价”功能的简短询问（如：Yes or no？Right？Any different ideas？Do you agree？what’s your opinion？）也视为提问的一种形式，称之为课堂程序性提问。与之在同一分类平台的提问形式还有课文理解性提问和现实情境性提问。课文理解性提问可按照提问的回答形式再分为展示型、参阅型和评估型。 展示型提问是“教师根据具体教学内容进行的提问。这类问题只要求学生对课文进行事实性的表层理解，并根据短时记忆或者查看课文找到答案”。参阅型提问是根据课文相关信息提问，“这类问题没有现成的答案，学生要结合个人的知识和课文所提供的信息进行综合分析”。 而评估型提问则“要求学生在理解课文的基础上进行深层次的逻辑思维，运用所学语言知识就课文的某个事件或观点发表自己的看法”。提问可以设计成如下三种方式：What is the…?（展示型问题）What’s the meaning of the phrase…here according to the context？（参阅型问题）What do you think of…?（评估型问题） 现实情境性提问主要是“根据学生的现实生活、现有知识或课堂上的情景状态等一些实际情况进行事实性提问，要求学生根据自己的实际情况进行回答”。 2.教学指令在课堂评价中的使用 评价在课堂教学中的语用功能是对学生参与课堂活动和完成学习任务等学习行为和学习成果质量的评估。评价可分为： 一般肯定或赞赏：That's OK.Right.Good！Great！Excellent！Wonderful！Well done！A good answer.Oh,you've done a good job.You are doing much better this time.You've made much progress recently. 一般否定或批评：I am sorry you are wrong.I don’t think you are right.It's a pity that your answer is not correct.That's almost right.Not quite right,can anyone help him？That's not quite right,any other answers?That's interesting！OK,Let's ask another person.A good try.Try next time. 提出质疑或纠正：Are you sure？We will have a discussion later after class.Think it over and try later.Your article is nearly well done except for some grammar mistakes.Nearly right,but you'd better….You should say like this….I think you may do it this way….That’s much better,but you forgot something when you pronounced…. 提出期望或建议：Well,your handwriting is quite good now！Keep it up！you've made good progress.Don't you think so？But there is still much room for improvement.I would suggest you practice more after class. 英语课堂教学指令虽然看起来有点复杂，但是对英语教学却起到了非常重要的作用，只要在教学中正确使用，一定会对我们的英语教学起到良好的带动作用。

蓝牙指令说明

蓝牙指令说明 通过置高PIO6进入设置方式，置低恢复正常状态，进入设置方式后波特率固定为9600，通信状态的波特率可通过指令设置。 指令格式如下： 1、进入设置方式后返回/r/n+OPEN:0/r/n 2、对于设置指令如果指令正确则返回：/r/nOK/r/n，如果错误则返回：/r/nERROR/r/n 3、对于查询类指令 例如AT+BAUD? 如果正确则返回：/r/nOK/r/n/r/n+BAUD:115200/r/n 如果错误则返回：/r/nERROR/r/n 我们所有用到的基本指令如下（以金瓯指令为例）： 1、AT+BAUD 这个指令只设置波特率(同样，查询的话也只返回波特率值)，例如：AT+BAUD=115200停止位和奇偶校验位通过指令AT+UARTMODE设置，模块默认的通讯波特率为 9600,N,8,1，AT模式波特率固定为9600,N,8,1 2、AT+AUTH 这个指令是设置是否需要鉴权的功能，也就是是否需要配对密码的功能 3、AT+PASSWORD 连接密钥 4、AT+NAME 名称中应该能识别空格。 5、AT+CLASS 例如：AT+CLASS=040680，这个直接跟6位数字，返回值也是这种形式 6、AT+ROLE 这个对于我们来说只要有主和从两种模式即可，也就是你们的服务端和客户端 7、AT+CLEARADDR 这条指令实际是配合AT+BIND使用的 8、AT+BIND 绑定地址时：对于从设备, 如果已经记忆地址，则不准被查询和配对，只能被它记忆的设备连接；对于主设备,如果已经记忆地址，则一直试着连接它记忆的设备；所以当绑定地址时，一旦设备记忆了地址，则连接只能在它与它记忆的设备之间建立，而不会与其它设备建立连接。所以，在绑定地址时，如果希望与其它设备建立连接，则必须清除记忆的地址。不绑定地址时：从设备可以被查询和配对；主设备连接记忆设备一定的次数失败后,主设备自动清除记忆的地址，并开始重新查询和配对新的设备。 连接固定的设备，绑定地址。 9、AT+ RADDR 这条指令与AT+LADDR格式相同即可。 10、AT+LADDR 该指令返回值的格式是：/r/nOK/r/n/r/n+LADDR:00025B00A5A5/r/n (地址不要用冒号隔开，或者其他格式) 11、AT+UARTMODE（这个我们一般不会用，默认N,8,1即可） AT+UARTMODE=, ：停止位 0：1 位停止位 1：2 位停止位

测试需要的命令(FTTB)

登录命令： 例子： LOGIN:::CTAG::UN=admin,PWD=admin; ZTE_113.12.238.52 2011-01-06 10:14:45 M CTAG COMPLD EN=0 ENDESC=No Error 握手命令 例子： SHAKEHAND:::CTAG::; ZTE_113.12.238.52 2011-01-06 10:15:39 M CTAG COMPLD EN=0 ENDESC=No Error LST-DEVINFO::ONUIP=222.171.142.73:1288771409262-38::; LST-DEVINFO::ONUIP=222.171.142.74:1288771409262-38::;

ZTE_113.12.238.52 2011-01-06 10:49:58 M CTAG COMPLD total_blocks=1 block_number=1 block_records=1 List of Device Info ----------------------------------------------------- DEVNAME DEVIP DT DEVER MEM CPU TEMPERATURE 技服F820 113.12.238.28 F820 V1.1.0P1 70 44 -- 查询单板信息 例子： LST-BRDINFO::ONUIP=222.171.142.73:CTAG::; LST-BRDINFO::ONUIP=222.171.142.74:CTAG::; ZTE_113.12.238.52 2011-01-06 10:50:30 M CTAG COMPLD

调度命令用语

一、封锁、开通区间及向封锁区间开行救援（路用）列车 l．＿站至＿站间＿行线，因＿，自＿时＿分（＿次列车到＿站）起，至＿时＿分（到另有通知时）止，区间封锁。 ⒉准＿站开＿次列车，进入＿站至＿站封锁区间＿km＿m至＿km＿m处，区间限速＿km／h，返回开＿次，凭引导（手）信号进站，限＿时＿分到站。 二、开通封锁区间 ⒈根据＿报告，＿站至＿站间__行线＿完毕（＿次列车已到达＿站），自＿时＿分起开通区间。 ⒉＿次列车在＿站至＿站间＿km＿m至＿km＿m处，限速＿km／h运行。 三、临时变更或恢复原行车闭塞法及反方向行车 1．＿站至＿站间＿行线因＿，自＿时＿分（＿次列车到＿站）起基本闭塞法停用，改用电话闭塞法行车。 2．准＿次列车在＿站至＿站间利用＿行线反方向运行，＿次列车到＿站后，恢复基本闭塞法行车。 四、恢复原行车闭塞法 ＿站至＿站间＿行线自接令时（＿次列车到＿站）起，恢复基本闭塞法行车。 五、双线改单线行车 ＿站至＿站间＿行线因＿，自＿时＿分（＿次列车到＿站）起区间封锁，＿站至＿站间改按单线行车，基本闭塞法停用，改用电话闭塞法行车。 六、恢复双线行车 根据＿报告，＿站至＿站间＿行线＿完毕（＿次列车已到达＿站），自＿时＿分起区间开通，同时恢复＿站至＿站间基本闭塞法及双线行车。 七、变更列车经路 准＿次列车由原＿径路，改经＿运行。 八、列车在区间内停车或返回 1．自接令时（＿次列车到＿站）起，＿站至＿站间基本闭塞法停用，改用电话闭塞法行车。＿站开＿次列车去＿站至＿站间＿行线＿km＿m处，返回＿次，限＿时＿分到＿站，凭引导（手）信号进站，到后恢复基本闭塞法行车。 2．＿站开＿次列车去＿站至＿站间＿行线＿km＿m至km＿m处，限＿时＿分到＿站。3．自接令时（＿次列车到＿站）起，＿站至＿站间＿行线基本闭塞法停用，改用电话闭塞法行车。准＿站开＿次列车反方向运行到＿站至＿站间＿行线＿km＿m至＿km＿m;返回__次，限＿时＿分到＿站，凭引导（手）信号进站，到后恢复基本闭塞法行车。 九、临时由区间内返回后部补机的列车 自接令时（＿次列车到＿站）起，＿站至＿站间＿行线基本闭塞法停用，改用电话闭塞法行车。＿次列车补机加补到＿公里＿米处，折返＿次返回＿站，凭引导（手）信号进站，列车到达＿站及补机返回＿站后，该线恢复基本闭塞法行车。 十、发生行车设备故障、灾害或列车中挂有限速的机车、车辆等，需要使列车临时减速运行，一停再开或特别注意运行 1．因＿站至＿站间＿行线＿km＿m至km＿m处，＿次列车运行至该处需一停再开，限速＿km／h运行。 2．＿次列车在＿站挂有＿辆（台），＿站至＿站间限速＿km／h运行。 十一、半自动闭塞区段使用故障按钮 1．根据＿站请求，现查明＿站至＿站间＿行线区间空闲，准＿站使用故障按钮办理闭塞机复原。

射线数字成像检测技术

射线数字成像检测技术 韩焱 (华北工学院现代元损检测技术工程中心，太原030051) 摘要：介绍多种射线数字成像(DR)系统的组成及成像机理，分析其性能指标、优缺点及应用领域。光子放大的DR系统(如图像增强器DR系统)实时性好，但适应的射线能量低，检测灵敏度相对较低；其它系统的检测灵敏度较高但成像时间较长。DR系统成像方式的主要区别在于射线探测器，除射线转换方式外，影响系统检测灵敏度的主要因素是散射噪声和量子噪声；可采用加准直器和光量子积分降噪的方法提高检测灵敏度。 关键词：射线检验；数字成像系统；综述 中图分类号：TGll5.28 文献标识码：A 文章编号：1000-6656(2003109-0468-04 DIGITAL RADIOGRAPHIC TECHNOLOGY HAN Yan （Center of Modern NDT ＆E, North China Institute of Technology, Taiyuan 030051, China) Abstract: The structure and imaging principle of digital radiographic （DR） systems are introduced. And thecharacteristics, performances, advantages, disadvantages and applications of the systems are analyzed. The DR sys-tern with photon amplification such as the DR system with intensifier can get real-time imaging, but it fits for lowerenergy and its inspection sensitivity is lower. The systems working with high energy can obtain higher sensitivity,while is time-eonsurning. The imaging way of a DR system depends on the detector used, and the factors influencinginspection sensitivity are the quantum noise from ray source and scatter noise besides the transform way of rays.Quantum integration noise reducer and collimator can be used to improve the inspection sensitivity of the system. Keywords:Radiography; Digital imaging system; Survey 射线检测技术作为产品质量检测的重要手段，经过百年的历史，已由简单的胶片和荧屏射线照相发展到了数字成像检测。随着信息技术、计算机技术和光电技术等的发展，射线数字成像检测技术也得到了飞速的发展，新的射线数字成像方法不断涌现，给射线探伤赋予了更广泛的内涵，同时也使利用先进网络技术进行远程评片和诊断成为可能。 目前工业中使用的射线数字成像检测技术主要包括射线数字直接成像检测技术(Digital Radio—graphy，简称DR)和射线数字重建成像检测技术，如工业CT(Industry Computed Tomography，简称ICT)。以下将在介绍DR检测系统组成的基础上，重点分析系统的成像原理、特点、特性及应用场合。 1 DR检测系统简介 DR检测系统组成见图1。按照图像的成像方式分为线扫描成像和面扫描成像；根据成像过程可分为直接和间接式DR系统。以下重点介绍直接DR系统。 图1 DR检测系统组成框图 1.1 直接式DR系统 直接DR成像系统主要分为图像增强器成像系统、平板型成像系统和线阵扫描成像系统等。 图2为图像增强器式DR系统，主要通过射线视频系统与数字图像处理系统集成实现。系统采用射线--可见光--电子--电子放大--可见光的光放大技术，是将射线光子由转换效率较高的主射线转换屏转换为可见光图像，可见光光子经光电转换变为电子，而后对电子进行放大，放大后的电子聚集在小屏上再次