J/ApJS/235/26 Ultradeep catalog of X-ray point sources in the GC (Zhu+, 2018)
An ultradeep Chandra catalog of X-ray point sources in the Galactic Center star
cluster.
Zhu Z., Li Z., Morris M.R.
<Astrophys. J. Suppl. Ser., 235, 26 (2018)>
=2018ApJS..235...26Z 2018ApJS..235...26Z
ADC_Keywords: Galactic center; X-ray sources
Keywords: Galaxy: center ; X-rays: binaries ; X-rays: stars
Abstract:
We present an updated catalog of X-ray point sources in the inner 500"
(∼20pc) of the Galactic center (GC), where the nuclear star cluster
(NSC) stands, based on a total of ∼4.5Ms of Chandra observations taken
from 1999 September to 2013 April. This ultradeep data set offers
unprecedented sensitivity for detecting X-ray sources in the GC, down
to an intrinsic 2-10keV luminosity of 1.0x1031erg/s. A total of 3619
sources are detected in the 2-8keV band, among which ∼3500 are
probable GC sources and ∼1300 are new identifications. The GC sources
collectively account for ∼20% of the total 2-8keV flux from the inner
250" region where detection sensitivity is the greatest. Taking
advantage of this unprecedented sample of faint X-ray sources that
primarily traces the old stellar populations in the NSC, we revisit
global source properties, including long-term variability, cumulative
spectra, luminosity function, and spatial distribution. Based on the
equivalent width and relative strength of the iron lines, we suggest
that in addition to the arguably predominant population of magnetic
cataclysmic variables (CVs), nonmagnetic CVs contribute substantially
to the detected sources, especially in the lower-luminosity group. On
the other hand, the X-ray sources have a radial distribution closely
following the stellar mass distribution in the NSC, but much flatter
than that of the known X-ray transients, which are presumably low-mass
X-ray binaries (LMXBs) caught in outburst. This, together with the
very modest long-term variability of the detected sources, strongly
suggests that quiescent LMXBs are a minor (less than a few percent)
population.
Description:
We utilized a total of 87 Chandra observations, which all have their
aim point targeted within ∼1' from Sgr A*, ensuring an optimal
point-spread function (PSF). Among these observations, 49 were taken
with the ACIS-I array, spanning 13.5yr (1999 September to 2013 April).
The other 38 observations, taken in 2012, had the ACIS-S and High
Energy Transmission Grating (HETG) in operation, chiefly to resolve
the accretion flow onto Sgr A*.
To gain insight on the differences and similarities between the X-ray
source populations in the nuclear bulge and the Galactic bulge, we
also utilized 13 ACIS-I observations of the so-called Limiting Window,
a field sampling the Galactic bulge at a projected distance of ∼80'
from Sgr A*, against a relatively low line-of-sight column density of
NH∼7x1021cm-2.
A log of the Chandra observations used in this work is given in Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 100 Chandra observation log
table2.dat 94 421 Catalog of the R<500" sources detected in
the 0.5-2keV band
table3.dat 153 3619 Catalog of the R<500" sources detected in
the 2-8keV band
table5.dat 26 576 Positions of removed sources originally found
by wavdetect
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
J/ApJ/502/558 : Catalog of ROSAT galaxy clusters (Vikhlinin+ 1998)
J/ApJ/589/225 : Chandra X-ray sources toward Galactic Center (Muno+, 2003)
J/ApJ/613/1179 : X-ray sources in Galactic Center (Muno+, 2004)
J/ApJS/165/173 : Chandra sources in Galaxy central 150pc (Muno+, 2006)
J/ApJS/169/401 : ChaMP X-ray point source catalog (Kim+, 2007)
J/ApJ/685/958 : Spitzer and Chandra sources in galactic center (Arendt+ 2008)
J/ApJ/703/30 : NIR counterparts to Chandra sources. I. (Mauerhan+, 2009)
J/ApJ/703/1323 : Stars in the Galaxy's nuclear cluster spectroscopy (Do+ 2009)
J/ApJ/706/223 : X-ray point sources near the Galactic Center (Hong+, 2009)
J/ApJS/181/110 : Galactic center X-ray sources (Muno+, 2009)
J/ApJ/721/1368 : X-ray emission from the Sombrero galaxy (Li+, 2010)
J/ApJ/721/1663 : NIR matches of X-ray sources in Gal. Center (DeWitt+, 2010)
J/ApJ/766/14 : Deep Chandra bulge field X-ray point sources (Morihana+, 2013)
J/ApJ/821/44 : Star motions in the nuclear cluster of the MW (Fritz+, 2016)
J/ApJS/224/40 : Catalog of Chandra ACIS point like sources (Wang+, 2016)
http://cxc.cfa.harvard.edu/ : Chandra X-ray Center home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- Field GC = Galactic center or LW = Limiting Window
(see the "Description" section above)
4- 8 I5 --- ObsID Chandra observation identifier
10 A1 --- m_ObsID Flag on ObsID 1561 (1)
12- 31 A20 "date" Start Starting time of observation (UT)
33- 37 F5.1 ks Exp [4.5/189.3] Exposure time
39- 44 A6 --- Inst Instrument
46- 54 F9.5 deg RAdeg Aim point right ascension (J2000)
56- 64 F9.5 deg DEdeg Aim point declination (J2000)
66- 70 F5.1 deg Roll Roll angle
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Note (1): We note that ObsID 1561 had two exposures separated by a few months
and essentially independent of each other.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/421] Index number
5- 13 F9.5 deg RAdeg [266.26/266.6] Right Ascension (J2000)
15- 23 F9.5 deg DEdeg [-29.2/-28.8] Declination (J2000)
25- 33 F9.7 arcsec ePos [0.05/3.3] Positional error
35- 39 I5 ct CTot [9/12560] Total 0.5-2 keV band counts
41- 45 F5.1 ct CBck [3/198.5] Background 0.5-2keV band counts
47 A1 --- l_CNet Limit flag on CNet
48- 54 F7.1 ct CNet [5.5/12391] Net 0.5-2keV band counts
56- 60 F5.1 ct E_CNet [/107.7]? Upper 1σ uncertainty in CNet
62- 66 F5.1 ct e_CNet [/112.2]? Lower 1σ uncertainty in CNet
68- 73 F6.2 10-7ph/cm/s S [0.01/262.8] Photon flux in 0.5-2keV band
75 A1 --- l_HR0 Limit flag on HR0
76- 82 F7.3 --- HR0 [-1/0.9] Soft color ratio (1)
84- 88 F5.3 --- E_HR0 [/0.6]? Upper 1σ uncertainty in HR0
90- 94 F5.3 --- e_HR0 [/0.7]? Lower 1σ uncertainty in HR0
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Note (1): The hardness ratio is defined as (CH-CS)/(CH+CS).
For HR0 CH is the 2-3.3keV band and CS is the 0.5-2keV band.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 --- Seq [1/3619] Index number
6- 14 F9.5 deg RAdeg [266.26/266.58] Right Ascension (J2000)
16- 24 F9.5 deg DEdeg [-29.2/-28.8] Declination (J2000)
26- 29 F4.2 arcsec ePos [0.03/0.8] Positional error
31- 35 I5 ct CTot [73/28299] Total 2-8 keV band counts
37- 42 F6.1 ct CBck [20.2/7012.5] Background 2-8keV
band counts
44 A1 --- l_CNet Limit flag on CNet
45- 51 F7.1 ct CNet [12.4/27371.5] Net 2-8keV band counts
53- 57 F5.1 ct E_CNet [6.5/234.4]? Upper 1σ uncertainty
in CNet
59- 63 F5.1 ct e_CNet [6.7/167]? Lower 1σ uncertainty
in CNet
65- 70 F6.2 10-7ph/cm2/s S0.5-2 [0.01/346.1]? Observed 0.5-2keV photon
flux (1)
72- 77 F6.2 10-7ph/cm2/s H2-8 [0.3/455.4] Observed 2-8keV photon flux
79- 85 F7.2 10-15mW/m2 F2-8 [0.7/1083.7] Absorption-corrected 2-10keV
energy flux
87 A1 --- l_HR0 Limit flag on HR0
88- 94 F7.3 --- HR0 Soft hardness ratio (2)
96-100 F5.3 --- E_HR0 [0.003/1.1]? Upper 1σ uncertainty
in HR0
102-106 F5.3 --- e_HR0 [0.003/1]? Lower 1σ uncertainty
in HR0
108 A1 --- l_HR1 Limit flag on HR1
109-115 F7.3 --- HR1 [-0.8/1] Medium hardness ratio (2)
117-121 F5.3 --- E_HR1 [0.006/1]? Upper 1σ uncertainty
in HR1
123-127 F5.3 --- e_HR1 [0.007/1]? Lower 1σ uncertainty
in HR1
129 A1 --- l_HR2 Limit flag on HR2
130-136 F7.3 --- HR2 [-0.9/1] Hard hardness ratio (2)
138-142 F5.3 --- E_HR2 [0.006/1.1]? Upper 1σ uncertainty
in HR2
144-148 F5.3 --- e_HR2 [0.006/1]? Lower 1σ uncertainty
in HR2
150-153 A4 --- n_Seq [,fimrx] Specific source notes for Seq (3)
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Note (1): In cases of non-detection in this band, a 1σ upper limit
is provided.
Note (2): The hardness ratios are defined as (CH-CS)/(CH+CS).
For HR0 CH is the 2-3.3keV band and CS is the 0.5-2keV band.
For HR1 CH is the 3.3-4.7keV band and CS is the 2-3.3keV band.
For HR2 CH is the 4.7-8keV band and CS is the 3.3-4.7keV band.
Note (3): Note as follows:
m = source with a counterpart in Muno+ (2009, J/ApJS/181/110);
ir = source with NIR a counterpart in Mauerhan+ (2010ApJ...710..706M 2010ApJ...710..706M);
x = X-ray transient tabulated in Degenaar+ (2015JHEAp...7..137D 2015JHEAp...7..137D);
f = probable foreground source.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/576] Index number (1)
6- 14 F9.5 deg RAdeg [266.26/266.58] Right Ascension (J2000)
16- 24 F9.5 deg DEdeg [-29.2/-28.8] Declination (J2000)
26 A1 --- n_Seq S: spurious source or E: extended source
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Note (1): Source sequence number assigned in order of increasing RA.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 23-Aug-2018