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CHANC150PC - Chandra Galactic Central 150 Parsecs Source Catalog

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Overview

The Chandra Catalog of X-Ray Sources in the Central 150 Parsecs of the Galaxy lists X-ray sources detected in a shallow Chandra survey of the inner 2 by 0.8 degrees of the Galaxy and in two deeper observations of the Radio Arches and Sgr B2. The catalog contains 1352 objects that are highly absorbed (N_H >~ 4 x 1022 cm-2) and are therefore likely to lie near the Galactic center (D ~ 8 kpc), and 549 less absorbed sources that lie within <~ 6 kpc of Earth, except that two bright, previously known LMXBs, 1E 1740.7-2942 and 2E 1743.1-2842, have been omitted because they were badly saturated in these survey images, and their positions and properties have been reported elsewhere (Marti et al. 2000, A&A, 363, 184; Porquet et al. 2003, A&A, 406, 299).

On the basis of the inferred luminosities of the X-ray sources and the expected numbers of various classes of objects, the authors suggest that the sources with L_X <~ 1033 ergs s-1 that comprise ~ 90% of the catalog are cataclysmic variables, and that the ~ 100 brighter objects are accreting neutron stars and black holes, young isolated pulsars, and Wolf-Rayet and O (WR/O) stars in colliding-wind binaries. They find that the spatial distribution of X-ray sources matches that of the old stellar population observed in the infrared, which supports their suggestion that most of the X-ray sources are old cataclysmic variables. However, they find that there is an apparent excess of ~ 10 bright sources in the Radio Arches region. That region is already known to be the site of recent star formation, so they suggest that the bright sources in this region are young high-mass X-ray binaries, pulsars, or WR/O star binaries.


Catalog Bibcode

2006ApJS..165..173M

References

A Chandra Catalog of X-ray Sources in the Central 150 pc of the Galaxy
     Muno M.P., Bauer F.E., Bandyopadhyay R.M., Wang Q.D.
    <Astrophys. J. Suppl. 165, 173 (2006)>
    =2006ApJS..165..173M

Provenance

This table was created by the HEASARC in August 2006 based on the version of Table 2 from the paper which was obtained from the electronic ApJ web site.

Parameters

Name
The designation for a Galactic center Chandra X-ray source (hence, the 'CXOGC' prefix) as given in the electronic version of Table 2. It should be noted that the generic Chandra prefix of 'CXO' is given in the printed version of this table.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-5 degrees in the original table.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-5 degrees in the original table.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The (90% confidence) positional uncertainty of the X-ray source, in arcseconds. This includes both statistical and systematic terms combined in quadrature. For the shallow observations, a systematic error of 0.6" has been assumed, while for observations with obsid values of 944 and 945 the systematic errors were assumed to be negligible.

ObsID
The Chandra observation identifier, or ObsID, of the observation in which the source was detected.

Offset
The angular offset of the X-ray source from the aimpoint of the observation in which the source was detected, in arcminutes. This was used in the calaculation by the authors of the statistical uncertainty in the position,

Exposure
The total live time that the source was observed with, in seconds. This was given in kiloseconds in the original table.

FB_Counts
The net (background-subtracted) full-band counts in the X-ray source. For most observations, this is the 1.0 - 8.0 keV spectral region, while for the observations with obsid values of 658, 944 and 945, it is the 0.5 - 8.0 keV spectral region.

FB_Counts_Neg_Err
The lower uncertainty (90% confidence) in the net full-band counts, computed using a Bayesian analysis with the simplifying assumption that the uncertainty in the background is negligible.

FB_Counts_Pos_Err
The upper uncertainty (90% confidence) in the net full-band counts, computed using a Bayesian analysis with the simplifying assumption that the uncertainty in the background is negligible. In cases where the 90% confidence interval for the net counts is consistent with 0, the sum of fb_counts and fb_counts_pos_err can be considered to be the upper limit to the actual fb_counts value.

Detection_Probability
The probability of detecting the source, given its location and exposure, estimated using Monte Carlo simulations (see Appendix A of the published paper for more details).

HR_Soft
The hardness ratio HR0, the so-called `soft color'. Colors are defined according to the usual definition HR = (H-L)/(H+L), where H and L are the net counts in high and low energy bands, respectively. The resulting ratio is bounded by -1 and +1. For the soft color, H is in the 2.0-3.3 keV band, and L is in the 0.5-2.0 keV band. Values are set to null (instead of -9.000 as in the published table) if both the 90% confidence interval of both bands contain zero counts.

HR_Soft_Neg_Err
The lower uncertainty in the soft color, HR0. Values are set to null (instead of -9.000 as in the published table), if the harder band is consistent with zero.

HR_Soft_Pos_Err
The upper uncertainty in the soft color, HR0. Values are set to null (instead of -9.000 as in the published table), if the softer band is consistent with zero.

HR_Hard
The hardness ratio HR2, the so-called `hard color'. Colors are defined according to the usual definition HR = (H-L)/(H+L), where H and L are the net counts in high and low energy bands, respectively. The resulting ratio is bounded by -1 and +1. For the hard color, H is in the 4.7-8.0 keV band, and L is in the 3.3-4.7 keV band. Values are set to null (instead of -9.000 as in the published table) if both the 90% confidence interval of both bands contain zero counts.

HR_Hard_Neg_Err
The lower uncertainty in the hard color, HR2. Values are set to null (instead of -9.000 as in the published table), if the harder band is consistent with zero.

HR_Hard_Pos_Err
The upper uncertainty in the hard color, HR2. Values are set to null (instead of -9.000 as in the published table), if the softer band is consistent with zero.

Flux
The photon flux of the X-ray source in the 0.5-8.0 keV energy range, in photon/cm2/s. This is computed by dividing the net counts in each subband by the total live time (units of s) and the mean value of the ARF in that energy range (units of cm^2: note that this value incorporates vraiations in exposure due to chip gaps and dead columns), and summing them, using negative values when they occur (not the upper limits).

Note_Flags
This parameter contains flags which indicate comments about the X-ray source. Sources are flagged with 's' if there was short-term variability within an observation, 'l' if there was long-term variability when comparing the flux in multiple observations, 'c' if the source was confused with its neighbors in some observations, so that the photometry was computed from a region enclosing < 90% of the flux in the point-spread function (PSF), and 'f' if the source was only detected below 2 keV.


Contact Person

Questions regarding the CHANC150PC database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 5-Mar-2012