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GALCENCXO - Galactic Center Chandra X-Ray Point Source Catalog

HEASARC
Archive

Overview

This table contains a catalog of 9017 X-ray sources identified in Chandra observations of a 2 degrees by 0.8 degrees 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 2.25 Ms of exposure. At the distance to the Galactic center (8 kpc), we are sensitive to sources with luminosities of 4 x 1032 erg s-1 (0.5-8.0 keV; 90% confidence) over an area of 1 degree2, and up to an order of magnitude more sensitive in the deepest exposure (1.0 Ms) around Sgr A*. The positions of 60% of the sources are accurate to <1 arcsecond (95% confidence), and 20% have positions accurate to <0.5 arcsec. The authors search for variable sources, and find that 3% exhibit flux variations within an observation, and 10% exhibit variations from observation-to-observation. They also find one source, CXOUGC J174622.7-285218, with a periodic 1745 s signal (1.4% chance probability), which is probably a magnetically accreting cataclysmic variable. The authors compare the spatial distribution of X-ray sources to a model for the stellar distribution, and find 2.8 sigma 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 a galactic lonitude ~ 0.1 degrees.

This tables was designed to be inclusive, so sources of questionable quality are included, according to the authors. For instance, 134 sources have net numbers of counts in the 0.5-8.0 keV band that are consistent with 0 at the 90% confidence level. These sources are only detected in a single band and are presumably either very hard or very soft, detected in single observations because they were transients, or detected in stacked observations with wvdecomp at marginal significance. The authors have chosen to include them because they passed the test based on Poisson statistics from Weisskopf et al. (2007, ApJ, 657, 1026).

The observations which were used to generate the source list herein tabulated are listed in Table 1 of the reference paper.

This HEASARC table GALCENCXO supercedes and replaces the previous HEASARC tables CHANGALCEN and CHANC150PC, which were based on Muno et al. (2003, ApJ, 589, 225) and Muno et al. (2006, ApJS, 165, 173), respectively.


Catalog Bibcode

2009ApJS..181..110M

References

A Catalog of X-Ray Point Sources from 2 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., Stolovoy, S.R., Wijnands, R., Wang, Q.D., Wang, Z.,
   Yusef-Zadeh, F.
  <Astrophys. J. Suppl. 181, 110 (2009)>
  = 2009ApJS..181..110M

Provenance

This table was created by the HEASARC in March 2009 based on the machine-readable versions of Table 2, 3 and 4 from the paper which were obtained from the electronic ApJ website. The information on short-term variability given in Table 5 of the reference paper was not included in this HEASARC table, notice.

HEASARC Implementation

A number of the parameters in this table, e.g., the photon flux parameters, are given to a different (usually lower) level of precision than in the sample tables in the published paper.

Parameters

Source_Number
A unique sequential identification mumber for each X-ray point source in the catalog.

Name
The recommended designation for the X-ray source, using the prefix 'CXOUGC J' (for Chandra X-ray Observatory, Galactic Plane, Ebisawa') and the truncated J2000 coordinates of the source, e.g., CXOUGC JHHMMSS.S-DDMMSS.

RA
The Right Ascension of the Chandra X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-5 degrees (0.036 arcseconds) in the originating table.

Dec
The Declination of the Chandra X-ray source in the selected equinox. This was given in J2000.0 coordinates to a precision of 10-5 degrees (0.036 arcseconds) in the originating table.

LII
The Galactic Longitude of the Chandra X-ray source.

BII
The Galactic Latitude of the Chandra X-ray source.

Error_Radius
The 95% positional uncertainty, i.e., the radius of the error circle, in arcseconds. There are 5810 sources with uncertainties <= 1 arcsec (half of which are within 7 arcmin of Sgr A*), and 1950 with uncertainties <= 0.5 arcsec (85% of which are within 7 armin of Sgr A*). (

Position_Flag
A flag indicating how the positions were derived. A "d" indicates that the position is from the mean position of events, a "c" indicates that it was derived by cross-correlating the image and the PSF, and a "w" indicates that 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.

Field_ID
The images in which the sources were identified. The tags "full", "2002", "2004", and "2005" indicate that a source was found in composite images of the Sgr A* field. All other values are the observations in which a source was detected. Two sources added manually are tagged with "hand".

Detect_Band
Additional information about how the sources were detected. The tag "full" refers to any source detected with wavdetect in the 0.5-8.0 keV band; "soft" sources were detected in the 0.5-2.0 keV but not the full band; "hard" sources were detected in the 4-8 keV band but neither of the other two bands. The tag "tile" indicates that the source was detected in a composite 0.5-8.0 keV image with the wvdecomp tool.

Off_Axis
The offset theta from the aim point, in arcminutes. If a source position was estimated from a composite image, theta is the mean offset weighted by the exposure. If a position was taken from a single observation, theta is the offset for that observation.

Num_Obs
The number of observations used to compute the photometry for the Chandra source.

Exposure
The exposure time, in seconds.

PSF_Fraction
The fraction of the point-spread function (PSF) enclosed by the source extraction region.

PSF_Energy
The fiducial energy of the PSF used to construct the source extraction region.

Min_Extraction_Radius
The smallest radius for the extraction region that was used for a source, in arcseconds. 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.

Limiting_Photon_Flux
The 50% completeness limit at the position of the source, in photons cm-2 s-1. Sources brighter than these completeness limits can be used to compute spatial and flux distributions, although the sensitivity map (Figure 9 of the reference paper) is needed to compute the corresponding survey area.

Quality_Flags
Flags denoting quality, and other information, as follows:

   "a" for sources used to register the astrometry of fields;
   "s" for sources variable on short timescales, 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 timescales, 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" for sources that may be part of an extended, diffuse feature
       (Muno et al. 2004, ApJ, 613, 326);
   "c" for sources confused with another nearby source;
   "g" for sources that fell near the edge of a detector in one or more
       observations;
   "b" for sources for which the source and the background spectra have a > 10%
       chance of being drawn from the same distribution according to a KS test;
   "x" for sources for which the 0.5-2.0 keV band photometry is inaccurate
       because the satellite was programmed to omit photons below 1 keV from
       the telemetry;
   "p" for sources that suffered from photon pile-up.
  

Log_Bck_Match_Prob
The log of the probability that the source and the background spectra are derived from the same distribution, according to a KS test. Large negative values indicate that the source and the background spectra are distinct, and therefore that the source is most likely real.

SB_Raw_Counts
The total number of counts in the 0.5-2.0 keV band in the source region.

SB_Bck_Counts
The estimated number of background counts in the 0.5-2.0 keV band in the source region.

SB_Counts_Limit
This parameter is set to '<' if the associated parameter is an upper limit.

SB_Counts
The net (background-subtracted) number of counts in the 0.5-2.0 keV band in the source region.

SB_Counts_Neg_Err
The lower uncertainty in the 0.5-2.0 keV band X-ray source net counts (90% confidence).

SB_Counts_Pos_Err
The upper Uncertainty in the 0.5-2.0 keV band X-ray source net counts (90% confidence).

HB_Raw_Counts
The total number of counts in the 2-8 keV band in the source region.

HB_Bck_Counts
The estimated number of background counts in the 2-8 keV band in the source region.

HB_Counts_Limit
This parameter is set to '<' if the associated parameter is an upper limit.

HB_Counts
The net (background-subtracted) number of counts in the 2-8 keV band in the source region.

HB_Counts_Neg_Err
The lower uncertainty in the 2-8 keV band X-ray source net counts (90% confidence).

HB_Counts_Pos_Err
The lower uncertainty in the 2-8 keV band X-ray source net counts (90% confidence).

SB_Photon_Flux
The Chandra source flux in the 0.5-2.0 keV band, in units of photons cm-2 s-1.

HB_Photon_Flux
The Chandra source flux in the 2-8 keV band, in units of photons cm-2 s-1.

Mean_Photon_Energy
The mean energy of photons in the source region, statistically corrected for the background, in keV.

HR0
The soft X-ray color (hardness ratio), HR_0. The authors used the net source counts to compute the hardness ratios (h - s)/(h + s), where h and s are the numbers of counts in the higher and lower energy bands, respectively. The resulting hardness ratios are bounded by -1.0 and +1.0. The authors defined a soft color using counts in the 2.0-3.3 keV and 0.5-2.0 keV bands, respectively.

HR0_Neg_Err
The calculated 90% lower uncertainty in the ratio HR_0, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

HR0_Pos_Err
The calculated 90% upper uncertainty in the ratio HR_0, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

HR1
The medium X-ray color (hardness ratio), HR_1. The authors used the net source counts to compute the hardness ratios (h - s)/(h + s), where h and s are the numbers of counts in the higher and lower energy bands, respectively. The resulting hardness ratios are bounded by -1.0 and +1.0. The authors defined a medium color using counts in the 3.3-4.7 keV bands and 2.0-3.3 keV bands, respectively.

HR1_Neg_Err
The calculated 90% lower uncertainty in the ratio HR_1, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

HR1_Pos_Err
The calculated 90% upper uncertainty in the ratio HR_1, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

HR2
The hard X-ray color (hardness ratio), HR_2. The authors used the net source counts to compute the hardness ratios (h - s)/(h + s), where h and s are the numbers of counts in the higher and lower energy bands, respectively. The resulting hardness ratios are bounded by -1.0 and +1.0. The authors defined a hard color using counts in the 4.7-8.0 keV and 3.3-4.7 keV bands, respectively.

HR2_Neg_Err
The calculated 90% lower uncertainty in the ratio HR_2, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

HR2_Pos_Err
The calculated 90% upper uncertainty in the ratio HR_2, using Equation 1.31 in Lyons (1991, A Practical Guide to Data Analysis for Physical Science Students, p. 26).

Location_Flag
A flag stating whether a source is in the foreground ("f") or near the Galactic center ("gc").

LT_Min_Observation
The ObsID of the observation in which the minimum flux of the Chandra X-ray source was observed.

LT_Min_Flux_Limit
This parameter is set to '<' if the associated parameter is an upper limit.

LT_Min_Flux
The minimum observed photon flux of the Chandra source, in units of photons cm-2 s-1.

LT_Min_Flux_Error
The 1-sigma uncertainty in the minimum observed photon flux of the Chandra source, in units of photons cm-2 s-1.

LT_Max_Observation
The ObsID of the observation in which the maximum flux of the Chandra X-ray source was observed.

LT_Max_Flux
The maximum observed photon flux of the Chandra source, in units of photons cm-2 s-1.

LT_Max_Flux_Error
The 1-sigma uncertainty in the maximum observed photon flux of the Chandra source, in units of photons cm-2 s-1.

LT_Max_Min_Ratio_Limit
This parameter is set to '>' if the associated parameter is a lower limit.

LT_Max_Min_Ratio
The ratio of the maximum to minimum photon flux of the Chandra source.

LT_Max_Min_Ratio_Neg_Err
The lower uncertainty in the ratio of the maximum to minimum photon flux of the Chandra source.

LT_Max_Min_Ratio_Pos_Err
The upper uncertainty in the ratio of the maximum to minimum photon flux of the Chandra source.

ST_Var_Flag
This HEASARC-created flag parameter indicates whether ("Y") or not ("N") the Chandra X-ray source exhibited short-term variability within any individual Chandra observation. Sources which showed such short-term variability are listed in Table 5 of the reference paper, and comprise 174 of the 9017 Chandra X-ray sources.


Contact Person

Questions regarding the GALCENCXO database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 25-Mar-2009