J/ApJ/780/83 X-ray binaries observed in M31 with Chandra (Barnard+, 2014)
Around 200 new X-ray binary IDs from 13 yr of Chandra observations of the M31
center.
Barnard R., Garcia M.R., Primini F., Li Z., Baganoff F.K., Murray S.S.
<Astrophys. J., 780, 83 (2014)>
=2014ApJ...780...83B 2014ApJ...780...83B
ADC_Keywords: Galaxies, nearby ; X-ray sources ; Binaries, X-ray ;
Active gal. nuclei
Keywords: galaxies: individual: M31 - methods: data analysis -
stars: black holes - X-rays: binaries - X-rays: general
Abstract:
We have created 0.3-10keV, 13yr, unabsorbed luminosity light curves
for 528 X-ray sources in the central 20' of M31. We have 174 Chandra
observations spaced at ∼1 month intervals due to our transient
monitoring program, deeper observations of the M31 nucleus, and some
public data from other surveys. We created 0.5-4.5keV structure
functions (SFs) for each source for comparison with the ensemble SF of
active galactic nuclei (AGN). We find 220 X-ray sources with
luminosities ≳1035erg/s that have SFs with significantly more
variability than the ensemble AGN SF, and which are likely X-ray
binaries (XBs). A further 30 X-ray sources were identified as XBs
using other methods. We therefore have 250 probable XBs in total,
including ∼200 new identifications. This result represents great
progress over the ∼50 XBs and ∼40 XB candidates previously identified
out of the ∼2000 X-ray sources within the D25 region of M31; it also
demonstrates the power of SF analysis for identifying XBs in external
galaxies. We also identify a new transient black hole candidate,
associated with the M31 globular cluster B128.
Description:
The central region of M31 has been observed with Chandra on a ∼monthly
basis for the last ∼13yr; we exclude periods when M31 cannot be viewed
due to orbital constraints (approximately March-May each year). We
have analyzed 112 observations obtained with the Advanced CCD Imaging
Spectrometer (ACIS; on the Chandra X-ray Observatory satellite, CXO)
and 62 High Resolution Camera (HRC; on the Chandra X-ray Observatory
satellite, CXO) observations, in order to discern the variability of
X-ray sources in this region.
Initial source detection was performed on a merged ACIS events file
created from observations performed from 1999 October to 2010 March;
the detection procedure followed that outlined by Wang
(2004ApJ...612..159W 2004ApJ...612..159W).
We compared our initial Chandra source list with the inventory from an
XMM-Newton survey of M31 performed by Stiele et al. 2011 (J/A+A/534/A55).
We found that the XMM-Newton catalog contained sources that were not
in our initial sample. We obtained lightcurves for each of those
sources and any that were significantly detected in our observations
were added to the source list.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 112 528 Summary of our findings for the 528 X-Ray sources
in our survey
table2.dat 69 120 *Spectral fits for sources with >200 net source
counts in at least one ACIS observation
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Note on table2.dat: ACIS=Advanced CCD Imaging Spectrometer (Chandra X-ray
Observatory satellite).
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See also:
V/143 : Revised Bologna Catalog of M31 clusters, V.5 (Galleti+ 2012)
J/A+A/536/A84 : X-ray variability of AGN (Vagnetti+, 2011)
J/A+A/534/A55 : Deep XMM-Newton Survey of M31 (Stiele+, 2011)
J/AJ/141/61 : Star clusters in M31. II. (Caldwell+, 2011)
J/AJ/137/94 : Star clusters in M31 (Caldwell+, 2009)
J/A+A/493/339 : XMM-Newton serendipitous Survey. V. (Watson+, 2009)
J/A+A/480/599 : XMM-Newton survey of M31 centre field (Stiele+, 2008)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- X-ray [1/528] Running sequence number of the source
<[BGP2014] NNN> in Simbad
5- 6 I2 h RAh Hour of Right Ascension (J2000) (1)
8- 9 I2 min RAm Minute of Right Ascension (J2000) (1)
11- 16 F6.3 s RAs Second of Right Ascension (J2000) (1)
18 A1 --- DE- Sign of the Declinaiton (J2000) (1)
19- 20 I2 deg DEd Degree of Declination (J2000) (1)
22- 23 I2 arcmin DEm Arcminute of Declination (J2000) (1)
25- 29 F5.2 arcsec DEs Arcsecond of Declination (J2000) (1)
31 A1 --- f_DEs [ab] Positional flag (2)
34- 37 F4.2 arcsec e_RAs 1σ uncertainty of Right Ascension
39- 42 F4.2 arcsec e_DEs 1σ uncertainty of Declination
44- 46 I3 --- N1 [1/109] Number of ACIS observations
(Advanced CCD Imaging Spectrometer)
48- 49 I2 --- N2 [0/63] Number of HRC observations
(High Resolution Camera)
51 A1 --- f_Class1 [!] Exclamation mark indicates classification
that were rejected for our Chandra location
52- 63 A12 --- Class1 Classification assigned by Stiele et al. 2011
(J/A+A/534/A55) (3)
65- 74 A10 --- Class2 Improvement on the Stiele et al. 2011
(J/A+A/534/A55) classification (3)
76- 83 F8.5 10+30W LX [0/44] Best fit constant luminosity to the
unabsorbed 0.3-10keV luminosity light curve
(in 1037erg/s) (4)
85- 91 F7.5 10+30W e_LX [0/0.2] Uncertainty in LX
92- 93 A2 --- f_LX Flag on LX (c=HRC observations ignored,
d=HRC observations included, e=fitted with
blackbody model) (5)
95- 99 I5 --- chi2 [1/61651] Model χ2
101-103 I3 --- DOF [3/170] Degrees of freedom
105 A1 --- l_Var [>] Lower limit flag on Var
106-110 F5.1 --- Var [0/320] Ranking of the object according to the
variability shown in its structure function
(Var=-log10(PAGN)) (6)
112 A1 --- f_Var [fg] Type of X-ray source (f=X-ray binary,
g=AGN) (7)
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Note (1): With respect to the B band image of M31 Field 5 in the Local Group
Survey provided by Massey et al. 2006 (J/AJ/131/2478).
Note (2): The two flags are:
a = Positions and uncertainties derived from XMM-Newton observations of
Stiele et al. 2011 (J/A+A/534/A55);
b = Position uncertainty obtained from a 9*9 binned image.
Note (3): The classification code is defined as follows:
XB = X-ray binary;
GC = Globular cluster;
star = Foreground star;
Gal = Galaxy;
AGN = Active galactic nuclei;
SNR = Supernova remnant;
SSS = SuperSoft Source;
H = Hard;
BHC = Black hole candidate;
T = Transient;
Nova = Novae;
U = ultraluminous X-ray source (exhibiting X-ray
luminosities>2*1039erg/s; Kaur et al., 2012A&A...538A..49K 2012A&A...538A..49K,
Nooraee et al., 2012A&A...542A.120N 2012A&A...542A.120N; Middleton et al.,
2013Natur.493..187M 2013Natur.493..187M; Barnard et al., 2013ApJ...772..126B 2013ApJ...772..126B);
var* = Variable star;
NC = X-ray source observed but Not Classified;
NE = X-ray source that had no entry at all;
X = known X-ray sources that do not appear in the XMM-Newton catalog
of Stiele et al. 2011 (J/A+A/534/A55);
[*] = Foreground star candidate;
[AGN] = Active galactic nuclei candidate;
[GC] = Globular cluster candidate;
[Gal] = Galaxy candidate;
[SNR] = Supernova remnant candidate;
[SSS] = SuperSoft Source candidate;
[XB] = X-ray binary candidate;
[Nova] = Novae candidate.
Note (4): We have created 0.3-10keV, 13yr, unabsorbed luminosity light curves
for 528 X-ray sources in the central 20' (∼4.5kpc) of M31.
Note (5): Here are more details about the three flags:
c = High Resolution Camera (HRC) observations ignored;
d = HRC observations included in luminosity fit but not structure function;
e = Very soft source modeled using an absorbed blackbody model with
NH=7*1020atom/cm2 and kT=0.05keV. Using our standard emission
model for these sources resulted in large systematic offsets between
ACIS and HRC luminosities.
Note (6): We have created 0.5-4.5keV structure functions for each target for
comparison with the ensemble AGN structure function created by Vagnetti
et al. 2011 (J/A+A/536/A84).
Var = -log10(PAGN) (Section 2.2), where
PAGN is the probability that the structure function is consistent with
3σ upper threshold for active galactic nuclei (AGN) variability.
Sources with a Var>2.6 are significantly more variable than expected for
typical AGN.
Note (7): The long explanations for the flags are:
f = Likely X-ray binary (XB);
g = Consistent with active galactic nuclei (AGN).
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- X-ray [31/512] Sequence number of the source
5- 16 A12 --- Model Emission model used (PO=POwer law,
BB=BlackBody, DBB=Disk BlackBody)
18- 22 F5.3 10+22/cm2 NH [0.06/0.87] Hydrogen column density
(in 1022atom/cm2) (1)
24- 28 F5.3 10+22/cm2 e_NH [0/0.48]? Uncertainty in NH
30- 37 F8.5 --- NHchi2 [0/77]? NH χ2 (2)
39- 41 I3 --- NHdof [1/104]? NH degrees of freedom (2)
43- 48 F6.4 --- Param [0.05/2.88] Parameter from emission model (3)
50- 55 F6.4 --- e_Param [0.001/0.9] Uncertainty in Param
57- 65 F9.5 --- Pchi2 [0/370]? Parameter χ2 (2)
67- 69 I3 --- Pdof [1/104]? Parameter degrees of freedom (2)
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Note (1): The absorption was fixed to Galactic line of sight absorption
(7*1020atom/cm2) for three sources (X-ray 175, X-ray 250, and
X-ray 287).
Note (2): If only one observation was fitted, then the χ2 and DOF is
blank. In cases with only 2 observations (1 degree of freedom), χ2
was often extremely low, and meaningless.
Note (3): Photon index Γ for power law (PO) model, kT/keV for blackbody
(BB) or disk blackbody (DBB) model.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 28-Jan-2015