J/ApJS/181/110 Galactic center X-ray sources (Muno+, 2009)
A catalog of X-ray point sources from two megaseconds of Chandra observations of
the Galactic center.
Muno M.P., Bauer F.E., Baganoff F.K., Bandyopadhyay R.M., Bower G.C.,
Brandt W.N., Broos P.S., Cotera A., Eikenberry S.S., Garmire G.P.,
Hyman S.D., Kassim N.E., Lang C.C., Lazio T.J.W., Law C., Mauerhan J.C.,
Morris M.R., Nagata T., Nishiyama S., Park S., Ramirez S.V., Stolovy S.R.,
Wijnands R., Wang Q.D., Wang Z., Yusef-Zadeh F.
<Astrophys. J. Suppl. Ser., 181, 110-128 (2009)>
=2009ApJS..181..110M 2009ApJS..181..110M
ADC_Keywords: X-ray sources ; Surveys ; Milky Way
Keywords: Galaxy: center - X-rays: stars
Abstract:
We present a catalog of 9017 X-ray sources identified in Chandra
observations of a 2°x0.8° field around the Galactic center.
This enlarges the number of known X-ray sources in the region by a
factor of 2.5. The catalog incorporates all of the ACIS-I observations
as of 2007 August, which total 2.25Ms of exposure. At the distance to
the Galactic center (8kpc), we are sensitive to sources with
luminosities of 4x1032erg/s (0.5-8.0keV; 90% confidence) over an
area of 1deg2, and up to an order of magnitude more sensitive in the
deepest exposure (1.0Ms) around Sgr A*. The positions of 60% of our
sources are accurate to <1" (95% confidence), and 20% have positions
accurate to <0.5". We search for variable sources, and find that 3%
exhibit flux variations within an observation, and 10% exhibit
variations from observation-to-observation. We also find one source,
CXOUGC J174622.7-285218, with a periodic 1745s signal (1.4% chance
probability), which is probably a magnetically accreting cataclysmic
variable. We compare the spatial distribution of X-ray sources to a
model for the stellar distribution, and find 2.8σ evidence for
excesses in the numbers of X-ray sources in the region of recent star
formation encompassed by the Arches, Quintuplet, and Galactic center
star clusters. These excess sources are also seen in the luminosity
distribution of the X-ray sources, which is flatter near the Arches
and Quintuplet than elsewhere in the field. These excess point
sources, along with a similar longitudinal asymmetry in the
distribution of diffuse iron emission that has been reported by other
authors, probably have their origin in the young stars that are
prominent at l∼0.1°.
Description:
As of 2007 August, the central 2x0.8° of the Milky Way has been
observed with the imaging array of the Chandra Advanced CCD Imaging
Spectrometer (ACIS-I) on numerous occasions (see table 1).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 84 88 Observations of the central 2°x0.8° of
the Galaxy
table2.dat 106 9017 Galactic center X-ray source locations and
extraction information
table3.dat 193 9017 Galactic center X-ray source photometry
table4.dat 89 856 Sources with long-term variability
table5.dat 108 198 Sources with short-term variability
--------------------------------------------------------------------------------
See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
J/ApJ/721/1663 : Near-IR matches of X-ray sources in GC (DeWitt+, 2010)
J/ApJ/703/30 : NIR counterparts to Chandra X-ray sources (Mauerhan+, 2009)
J/ApJ/685/958 : Spitzer and Chandra sources in galactic center (Arendt+ 2008)
J/ApJS/165/173 : Chandra sources in Galaxy central 150pc (Muno+, 2006)
J/ApJ/613/1179 : X-ray sources in Galactic Center (Muno+, 2004)
J/ApJ/589/225 : Chandra X-ray sources toward GC (Feigelson+, 2003)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "YYYY/MM/DD" Obs.date Observation date
12- 19 A8 "h:m:s" Obs.time Observation start time (UT)
21- 24 I4 --- ObsID [658/8567] Observation identifier
25 A1 --- m_ObsID [ab] Component of observation identifier
27- 40 A14 --- Target Target name
42- 46 F5.1 ks tExp Exposure time
48- 56 F9.5 deg RAdeg Right Ascension in degrees (J2000)
58- 66 F9.5 deg DEdeg Declination in degrees (J2000)
68- 72 F5.1 deg Roll Roll angle of the satellite
74- 75 I2 --- NIR ?=- number of 2MASS sources used (1)
77- 79 I3 --- NX ?=- number of X-ray matches used (2)
81- 84 F4.2 arcsec Sigma 1σ uncertainties on astrometry (3)
--------------------------------------------------------------------------------
Note (1): to align the astrometry for the deepest observations at any point.
Note (2): to align the astrometry of the shallower observations to the deepest
ones.
Note (3): as determined from the standard deviations in the means of the offsets
between the input and trial catalogs.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 -- Seq [1/9017] Source number
6- 20 A15 -- CXOGC IAU name (HHMMSS.s-DDMMSS)
22- 30 F9.5 deg RAdeg Right Ascension in degrees (J2000)
32- 40 F9.5 deg DEdeg Declination in degrees (J2000)
42- 44 F3.1 arcsec ePos Positional uncertainty, error circles (95%)
46 A1 -- m [cdw] Method for deriving position (1)
48- 52 A5 -- Field Field in which source was detected (2)
54- 57 A4 -- Band Band in which source was detected (3)
59- 62 F4.1 arcmin Offset Offset from aimpoint (4)
64- 65 I2 -- Nobs Number of observations covering source
67- 73 I7 s Exp Live time at source position
75- 78 F4.2 -- PSF Fraction of PSF encompassed by source region
80- 83 F4.2 keV EPSF Energy at which PSF was estimated
85- 88 F4.1 arcsec RadMin Minimum radius of source extraction region (5)
90- 98 E9.2 ph/cm2/s FSENS Completness limit (50%) at source position (6)
100-106 A7 -- Flags Quality Flags and other information (7)
--------------------------------------------------------------------------------
Note (1): Flag indicating how the positions were derived as follows :
d = position is from the mean position of events,
c = it was derived by cross-correlating the image and the PSF,
w = it was derived from a wavelet algorithm. Sources marked with a "w" are
likely to be confused with a nearby source, or in a region of high
background.
Note (2): Tags as follows :
full, 2002, 2004, 2005 = source was found in composite images of the Sgr A*
field.
hand = Two sources added manually.
All other values are the observations in which a source was detected.
Note (3): Tag as follows:
full = any source detected with wavdetect in the 0.5-8.0keV band;
soft = sources were detected in the 0.5-2.0keV but not the full band;
hard = sources were detected in the 4-8keV band but neither of the other two
bands.
tile = source was detected in a composite 0.5-8.0keV image with wvdecomp.
Note (4): If a source position was estimated from a composite image, this is the
mean offset weighted by the exposure. If a position was taken from a
single observation, this is the offset for that observation.
Note (5): This is determined from the observation in which the source was
closest to the aim point. It is also an absolute upper bound to the
positional uncertainty for a source.
Note (6): Sources brighter than these completeness limits can be used to compute
spatial and flux distributions, although the sensitivity map (Figure
9) is needed to compute the corresponding survey area.
Note (7): Flags as follows :
a = sources used to register the astrometry of fields
c = sources confused with another nearby source;
g = sources that fell near the edge of a detector in one or more observations;
b = sources four which the source and background spectra have a >10% chance of
being drawn from the same distribution according to a KS test;
s = sources variable on short time scales, as indicated by probabilities of
<0.1% that the event arrival times for at least one observation were
consistent with a uniform distribution according to the KS test;
l = for sources that were variable on long time scales, as indicated by a
probability of <0.1% that the fluxes for all observations were consistent
with a uniform distribution according to the KS test;
e = sources that may be part of an extended, diffuse feature (Muno et al.,
2004ApJ...613..326M 2004ApJ...613..326M);
x = sources for which the 0.5-2.0keV band photometry is inaccurate because the
satellite was programmed to omit photons below 1keV from the telemetry;
p = sources that suffered from photon piled-up.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 -- Seq [1/9017] Source number
6- 20 A15 -- CXOGC IAU name (HHMMSS.s+DDMMSS; J2000)
22- 27 F6.2 -- PKS ?=-99.99 Log of probability that source and
background spectrum are from the same
distribution according to a KS test (8)
28 A1 -- f_PKS [i] i=Infinite value
30- 35 I6 ct Sct.tot Total counts 0.5-2.0keV in source region
37- 42 F6.1 ct Sct.bg Background counts 0.5-2.0keV in source region
44 A1 -- l_Sct.net [<] Limit flag on 0.5-2.0keV net counts (9)
46- 53 F8.1 ct Sct.net Net counts 0.5-2.0keV in source region
55- 60 F6.1 ct e_Sct.net [-39/]? Lower uncertainty on 0.5-2.0keV net
counts (90% confidence)
62- 67 F6.1 ct E_Sct.net ? Upper uncertainty on 0.5-2.0keV net counts
(90% confidence) (9)
69- 74 I6 ct Hct.tot Total counts 2-8keV in source region
76- 81 F6.1 ct Hct.bg Background counts 2-8keV in source region
83 A1 -- l_Hct.net [<] Limit flag on 2-8keV net counts (9)
85- 92 F8.1 ct Hct.net Net counts 2-8keV in source region
94- 99 F6.1 ct e_Hct.net [-39/]? Lower uncertainty on 2-8keV net
counts (90% confidence)
101-106 F6.1 ct E_Hct.net ? Upper uncertainty on 2-8keV net counts
(90% confidence) (9)
108-116 E9.2 ph/cm2/s Sflux Photon flux 0.5-2.0keV
118-126 E9.2 ph/cm2/s Hflux Photon flux 2-8keV
128-130 F3.1 keV Background-corrected mean observed photon
energy
132-137 F6.3 -- HR0 [-1,1]?=-9.0 Soft color (10)
139-144 F6.3 -- e_HR0 [0,2]?=-9.0 90% Lower uncertainty on HR0 (10)
146-151 F6.3 -- E_HR0 [0,2]?=-9.0 90% Upper uncertainty on HR0 (10)
153-158 F6.3 -- HR1 [-1,1]?=-9.0 Medium color (10)
160-165 F6.3 -- e_HR1 [0,4]?=-9.0 90% Lower uncertainty on HR1 (10)
167-172 F6.3 -- E_HR1 [0,2]?=-9.0 90% Upper uncertainty on HR1 (10)
174-179 F6.3 -- HR2 [-1,1]?=-9.0 Hard color (10)
181-186 F6.3 -- e_HR2 [0,2]?=-9.0 90% Lower uncertainty on HR2 (10)
188-193 F6.3 -- E_HR2 [0,2]?=-9.0 90% Upper uncertainty on HR2 (10)
--------------------------------------------------------------------------------
Note (8): Large negative values indicate that the source and the background
spectra are distinct, and therefore that the source is most likely real.
Note (9): the limit flag is set ('<') when the counts are compatible with
a non-detection at the 90% confidence level; the upper limit at that
confidence limit is given by the E_Sct.net or E_Hct.net value.
Note (10): Colors are defined according to (H-L)/(H+L), where H and L are
the net counts in high and low energy bands, respectively.
* for the soft color (HR0): H is 2.0-3.3keV, L is 0.5-2.0keV.
* for the medium color (HR1): H is 3.3-4.7keV, L is 2.0-3.3keV.
* for the hard color (HR2): H is 4.7-8.0keV, L is 3.3-4.7 keV.
Note that when the HR=-1 or 1, we have limit value intervals in the
three columns HR and lower, upper errors:
For examples: -1.000 -9.000 0.445 = ←0.555 and
1.000 0.969 -9.000 = >0.031.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 -- Seq [1/8962] Source number
6- 20 A15 -- CXOGC IAU name (HHMMSS.s+DDMMSS)
22- 23 A2 -- Loc [f/gc] f = Foreground, gc = Galactic center
25- 28 I4 -- ObsMin Observation ID with lowest measured flux
29 A1 -- m_ObsMin [ab] Composant of observation identifier
31- 37 E7.1 ph/cm2/s Fmin Minimum flux
39- 45 E7.1 ph/cm2/s e_Fmin Uncertainty on minimum flux (1 sigma)
47- 50 I4 -- ObsMax Observation ID with highest measured flux
51 A1 -- m_ObsMax [ab] Composant of observation identifier
53- 59 E7.1 ph/cm2/s Fmax Maximum flux
61- 67 E7.1 ph/cm2/s e_Fmax Uncertainty on maximum flux (1 sigma)
69- 75 F7.1 -- Ratio Ratio of maximum to minimum flux
77- 82 F6.1 -- e_Ratio ?=-1.0 Lower bound on Ratio
84- 89 F6.1 -- E_Ratio ?=-1.0 Upper bound on Ratio
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 -- Seq [1/8961] Source number
6- 20 A15 -- CXOGC IAU name (HHMMSS.s+DDMMSS)
22- 23 A2 -- Loc [f/gc] f = Foreground, gc = Galactic center
25- 28 I4 -- ObsID Observation in which variability was detected
29 A1 -- m_ObsID [ab] Composant of observation identifier
31- 34 I4 -- Odd [10/1000] Odd prior used in Bayesian Blocks
analysis (1)
36- 37 I2 -- Nbl [2/10] Number of blocks found
39- 44 I6 s Dur [752/111856] Duration of the block with the
highest flux
46- 52 E7.1 ph/cm2/s Fmin [0/0.0021] Minimum flux
54- 60 E7.1 ph/cm2/s e_Fmin Lower bound on minimum flux (1 sigma)
62- 68 E7.1 ph/cm2/s E_Fmin Upper bound on minimum flux (1 sigma)
70- 76 E7.1 ph/cm2/s Fmax [1e-06/0.0026] Maximum flux
78- 84 E7.1 ph/cm2/s e_Fmax Lower bound on maximum flux (1 sigma)
86- 92 E7.1 ph/cm2/s E_Fmax Upper bound on maximum flux (1 sigma)
94-100 F7.2 -- Ratio [0.84/247.48] Ratio of maximum to minimum flux
102-108 F7.2 -- e_Ratio ?=-1.0 Uncertainty on Ratio
--------------------------------------------------------------------------------
Note (1): Odd ratio at which the Bayesian blocks algorithm identified a source
as variable.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 20-Oct-2009