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OMEGCENCX2 - Omega Centauri Globular Cluster Chandra Deep Survey X-Ray Point Source Catalog

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Overview

The authors identify 233 X-ray sources, of which 95 are new, in a 222-ks exposure of omega Centauri with the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer detector. The limiting unabsorbed flux in the core is fX(0.5-6.0keV) ~= 3 x 10-16 erg/s/cm2 (Lx ~= 1 x 1030 erg/s at 5.2kpc). The authors estimate that ~60 +/- 20 of these are cluster members, of which ~30 lie within the core (rc = 155 arcsec), and another ~30 between 1-2 core radii. They identify four new optical counterparts, for a total of 45 likely identifications. Probable cluster members include 18 cataclysmic variables (CVs) and CV candidates, one quiescent low-mass X-ray binary, four variable stars, and five stars that are either associated with omega Cen's anomalous red giant branch or are sub-subgiants. The authors estimate that the cluster contains 40 +/- 10 CVs with L_x_> 1031 erg/s, confirming that CVs are underabundant in omega Cen relative to the field. Intrinsic absorption is required to fit X-ray spectra of six of the nine brightest CVs, suggesting magnetic CVs, or high-inclination systems. Though no radio millisecond pulsars (MSPs) are currently known in omega Cen, more than 30 unidentified sources have luminosities and X-ray colors like those of MSPs found in other globular clusters; these could be responsible for the Fermi-detected gamma-ray emission from the cluster. The authors identify a CH star as the counterpart to the second brightest X-ray source in the cluster and argue that it is a symbiotic star. This is the first such giant/white dwarf binary to be identified in a globular cluster.

The data were obtained over two long exposures of omega Cen using the imaging array of the Chandra X-ray Observatory's ACIS-I on 2012 April 16 and 17. The data sets have a combined exposure time of ~222ks (173.7 and 48.5ks for ObsIDs 13726 and 13727, respectively).


Catalog Bibcode

2018MNRAS.479.2834H

References

A deep X-ray Survey of the globular cluster omega Centauri.
    Henleywillis S., Cool A.M., Haggard D., Heinke C., Callanan P., Zhao Y.
   <Mon. Not. R. Astron. Soc., 479, 2834-2852 (2018)>
   =2018MNRAS.479.2834H

Provenance

This table was created by the HEASARC in June 2018 based upon the CDS Catalog J/MNRAS/479/2834 file table1.dat.

Parameters

Source_ID
A unique source identifier. The authors adopted the same labeling convention for sources used by Haggard et al. (2009), who identified 180 sources in the first epoch of Chandra data, 138 of which are recovered here. All sources were assigned a three- or four-character ID based on the radial distance from the center of the cluster and the azimuthal angle. The leading one or two characters is a number between 1 and 11 (inclusive) equal to the radial offset rounded to 1 arcmin. The second (or third, in the case of a four-character source_id) character is a number between 1 and 4 identifying the quadrant in which the source falls. The final (i.e., the third or fourth) character is a letter based on azimuthal angle, increasing anticlockwise. Original labels were kept for re-detected sources; source IDs for new sources begin with the next available letter. All new sources have source_flag = "Y".

Name
The catalog source designation registered with the CDS Dictionary of Nomenclature of Celestial Objects. Since many of the sources are based on the Haggard et al. (2009) catalog, this catalog uses the naming convention of the prefix of '[HCD2009] ' concatenated with the source_id.

Source_Flag
A flag [Y] indicates that the name is assigned in this work; i.e., this is a new source.

RA
The Right Ascension of the Chandra X-ray source in the selected equinox. This parameter was given in J2000.0 equatorial coordinates to a precision of 0.001 seconds of time in the original table.

Dec
The Declination of the Chandra X-ray source in the selected equinox. This parameter was given in J2000.0 equatorial coordinates to a precision of 0.01 arcseconds in the original 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% confidence error radius calculated using Eq. 5 of Hong et al. (2005ApJ...635..907H).

Radial_Distance
The radial distance from Anderson & van der Marel (2010, Cat. J/ApJ/710/1032) cluster center (RA=13 26 47.24, DE=-47 28 46.45) in units of the core radius (rc = 155 arcsec).

MB_Total_Counts
The detected raw medium (0.5-4.5keV) band X-Ray counts. The counts from the level=2 event files were extracted from each individual dataset and summed.

MB_Counts
The corrected medium (0.5-4.5keV) band X-Ray counts, based on background subtraction, aperture correction, and exposure correction.

SB_Total_Counts
The detected raw soft (0.5-1.5keV) band X-Ray counts. The counts from the level=2 event files were extracted from each individual dataset and summed.

SB_Counts
The corrected soft (0.5-1.5keV) band X-Ray counts, based on background subtraction, aperture correction, and exposure correction.

HB_Total_Counts
The detected raw hard (1.5-6 keV) band X-Ray counts. The counts from the level=2 event files were extracted from each individual dataset and summed.

HB_Counts
The corrected hard (1.5-6keV) band X-Ray counts, based on background subtraction, aperture correction, and exposure correction.

Hardness_Ratio
The logarithm of the corrected soft-to-hard X-Ray count ratio.

MB_Flux
The medium (0.5-4.5keV) band X-Ray unabsorbed flux, which assumes a power law model with photon index of 1.4 and hydrogen column density of NH = 9 x 1020 cm-2 and uses the tbabs model with the abundances from Wilms, Allen & McCray (2000). The fluxes are exposure-time-weighted averages of the fluxes determined by running SRCFLUX on each level=2 event file separately.

TB_Flux
The total (0.5-6.0keV) band X-Ray unabsorbed flux, which assumes a power law model with photon index of 1.4 and hydrogen column density of NH = 9 x 1020 cm-2 and uses the tbabs model with the abundances from Wilms, Allen & McCray (2000). The fluxes are exposure-time-weighted averages of the fluxes determined by running SRCFLUX on each level=2 event file separately.

SB_Flux
The soft (0.5-2.0keV) band X-Ray unabsorbed flux, which assumes a power law model with photon index of 1.4 and hydrogen column density of NH = 9 x 1020 cm-2 and uses the tbabs model with the abundances from Wilms, Allen & McCray (2000). The fluxes are exposure-time-weighted averages of the fluxes determined by running SRCFLUX on each level=2 event file separately.

FluxVar
The 0.5-6.0keV band flux ratio between the 2012 and 2000 data, indicating variability between these observations.

FluxVar_Flag
The flag [g] indicates that fluxes determined using a spectrum appropriate for this object show no change from 2000 to 2012.

Optical_ID
The optical identifications for previously known sources. These come from Haggard et al. (2009, Cat. J/ApJ/697/224) Cool et al. (2013ApJ...763..126C), and this work; 'NV' and 'V' IDs are variable stars from Kaluzny et al. (2004, Cat. J/A+A/424/1101); parentheses indicate that stars are non-members according to Bellini et al. (2009, Cat. J/A+A/493/959).


Contact Person

Questions regarding the OMEGCENCX2 database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Tuesday, 04-Jun-2019 14:17:46 EDT