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CCOSMOSCAT - Chandra COSMOS (C-COSMOS) Survey X-Ray Point Source Catalog

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Overview

The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that has imaged the central 0.5 deg2 of the COSMOS field (centered at RA, Dec of 10 hours , +02 degrees) with an effective exposure of ~ 160 ks, and an outer 0.4 deg2 area with an effective exposure of ~ 80 ks. The limiting source detection depths are 1.9 x 10-16 erg cm-2 s-1 in the soft (0.5 - 2 keV) band, 7.3 x 10-16 erg cm-2 s-1 in the hard (2 - 10 keV) band, and 5.7 x 10-16 erg cm-2 s-1 in the full (0.5 - 10 keV) band. In this paper, the authors describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of < 2 x 10-5 (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~ 50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (+/-12%) exposure across the inner 0.5 deg2 field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting log N-log S curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper.

Supporting data products for this table (including images, event files and exposure maps) will be available at the "Chandra COSMOS Survey" web site (http://chandracosmos.cfa.harvard.edu/reports/analysis/20090310_TA_source_catalog _2.1/) and at IRSA. At the Chandra COSMOS Survey web site, it will also be possible to browse a database that includes "postage stamps" of the X-ray data for each source, along with the multiwavelength optical and infrared data, including the I-band, K-band, and Spitzer 3.6-micron (Band 1) images used in Paper III (Civano et al. 2009, in preparation) to identify the sources. The HEASARC will link to the X-ray data products from this current table when these become publically available.


Catalog Bibcode

2009ApJS..184..158E

References

The Chandra COSMOS Survey. I. Overview and Point Source Catalog

	Elvis, M., Civano, F., Vignali, C., Puccetti, S., Fiore, F.,
        Cappelluti, N., Aldcroft, T.L., Fruscione, A., Zamorani, G.,
        Comastri, A., Brusa, M., Gilli, R., Miyaji, T., Damiani, F.,
        Koekemoer, A.M., Finoguenov, A., Brunner, H., Urry, C.M.,
        Silverman, J., Mainieri, V., Hasinger, G., Griffiths, R.,
        Carollo, M., Hao, H., Guzzo, L., Blain, A., Calzetti, D., Carilli, C.,
        Capak, P., Ettori, S., Fabbiano, G., Impey, C., Lilly, S.,
        Mobasher, B., Rich, M., Salvato, M., Sanders, D.B., Schinnerer, E.,
        Scoville, N., Shopbell, P., Taylor, James E., Taniguchi, Y.,
        Volonteri, M.
       <Astrophys. J. Suppl. 184, 158-171 (2009)>
       =2009ApJS..184..158E

Provenance

This table was created by the HEASARC in November 2009 based on an electronic version of the C-COSMOS Catalog which was obtained from the Atrophysical Journal web site.

Parameters

Name
The Chandra source name, following the standard IAU position-based convention with the prefix "CXOC" for "Chandra X-ray Observatory COSMOS" survey and the J2000.0 source coordinates.

Source_Number
The Chandra source number. Source numbers are in order of detection: first those detected in the full band with detml >= 10.8, followed by those detected in the soft band only and by those detected in the hard band only.

Alt_Name
An alternative designation for the Chandra source using the 'ECV2009' prefix for Elvis, Civano, Vignali (2009) and the source number, in the style (expected to be) recommended by the Dictionary of Nomenclature of Celestial Objects.

RA
The Right Ascension of the Chandra source in the selected equinox. This was given in J2000.0 coordinates to a precision of 1 microdegree (3.6 mas).

Dec
The Declination of the Chandra source in the selected equinox. This was given in J2000.0 coordinates to a precision of 1 microdegree (3.6 mas).

LII
The Galactic Longitude of the Chandra source.

BII
The Galactic Latitude of the Chandra source.

Error_Radius
The Chandra source positional error pos_err = sqrt[sigma(RA)2 + sigma(Dec)2], in arcseconds, computed using the following equation Pos_error = PSF_radius/sqrt(S), where S is the number of net source counts, after the subtraction of the background, in a circular region of radius corresponding to the 50% encircled energy in the field where the source is at the lowest off-axis angle (Paper II, Puccetti et al. 2009, ApJS, submitted).

Count_Rate
The count rate CR in the full energy band (0.5 - 7 keV), in ct/s. These are effective count rates that would apply if the source had been observed at the aim point in every pointing, i.e., computed by dividing the best fit counts for the source by the effective exposure time at the position of the source (the effective exposure time includes corrections for vignetting, dither, bad pixels and spatially dependent quantum efficiency).

Count_Rate_Error
The error in the count rate in the full energy band (0.5 - 7 keV), in ct/s. The count rate error E(CR) at 68% confidence level was computed using the equation E(CR) == sqrt[C_(s,90%) + (1+a)B_90%]/0.9T, where C_s are the source counts estimated by EMLdetect, corrected to an area including 90% of the PSF, B are the background counts evaluated from the background rate (counts pixel-1) estimated by EMLdetect multiplied for an area of radius R_w, which is the mean of the radii, corresponding to 90% enclosed counts fraction (ECF) of each observation, weighted by the observation exposure relative to the total exposure, and T is the vignetting corrected exposure time at the position of the source from the exposure maps. The authors use a value of a = 0.5, to allow for uncertainties in the background, which is computed through the EMLdetect procedure: see Paper II, Puccetti et al. (2009, ApJS, submitted) for more details.

Flux
The full-band 0.5 - 10 keV flux of the Chandra source, in erg cm-2 s-1, computed converting count rates CR to fluxes F using the following formula: F = CR/(CF*1011), where CF is the energy conversion factor 0.742 counts erg-1 cm2) appropriate for a power-law spectrum with spectral index Gamma = 1.4 and Galactic column density N_H = 2.7 x 1020 cm-2. For sources not detected in this band, a 90% upper limit is reported (see Paper II for details). Notice that the energy ranges used for the full-band count rates and fluxes are different (0.5 - 7.0 keV versus 0.5 - 10.0 keV, respectively), as discussed in Section 2 of the reference paper.

Flux_Error
The error in the full-band 0.5 - 10 keV flux of the Chandra source, in erg cm-2 s-1, computed from the count rate error in the same way that the flux is computed from the count rate.

SNR
The full-band signal-to-noise ratio of the Chandra source.

Exposure
The full-band exposure time derived from the exposure map, in seconds (converted by the HEASARC from the ks units given in the original table).

Counts
The aperture photometry counts in the full band (0.5 - 7 keV) as derived from event data for each individual Obs_id and CCD where a source lands. Notice that this will not necessarily be equal to the product of the count rate and the exposure time. Circular extraction regions corresponding to the 90% ECF for that observation are centered on the source R.A. and Dec. The individual photometry values are then merged to produce a single set of values accounting for the ECF for each Obs_ID, given the different extraction regions needed.

Counts_Error
The error in the full-band (0.5 - 7 keV) aperture photometry net counts.

AP_Exposure
The exposure time in the full-band (0.5 - 7 keV) from the same region used to generate the aperture photometry, in seconds (converted by the HEASARC from the ks units given in the original table).

SB_Count_Rate
The count rate CR in the soft energy band (0.5 - 2 keV), in ct/s. These are effective count rates that would apply if the source had been observed at the aim point in every pointing, i.e., computed by dividing the best fit counts for the source by the effective exposure time at the position of the source (the effective exposure time includes corrections for vignetting, dither, bad pixels and spatially dependent quantum efficiency).

SB_Count_Rate_Error
The error in the count rate in the soft energy band (0.5 - 2 keV), in ct/s. The count rate error E(CR) at 68% confidence level was computed using the equation E(CR) == sqrt[C_(s,90%) + (1+a)B_90%]/0.9T, where C_s are the source counts estimated by EMLdetect, corrected to an area including 90% of the PSF, B are the background counts evaluated from the background rate (counts pixel-1) estimated by EMLdetect multiplied for an area of radius R_w, which is the mean of the radii, corresponding to 90% enclosed counts fraction (ECF) of each observation, weighted by the observation exposure relative to the total exposure, and T is the vignetting corrected exposure time at the position of the source from the exposure maps. The authors use a value of a = 0.5, to allow for uncertainties in the background, which is computed through the EMLdetect procedure: see Paper II, Puccetti et al. (2009, ApJS, submitted) for more details.

SB_Flux
The soft-band 0.5 - 2 keV flux of the Chandra source, in erg cm-2 s-1, computed converting count rates CR to fluxes F using the following formula: F = CR/(CF*1011), where CF is the energy conversion factor 1.837 counts erg-1 cm2) appropriate for a power-law spectrum with spectral index Gamma = 1.4 and Galactic column density N_H = 2.7 x 1020 cm-2. For sources not detected in this band, a 90% upper limit is reported (see Paper II for details).

SB_Flux_Error
The error in the soft-band 0.5 - 2 keV flux of the Chandra source, in erg cm-2 s-1, computed from the count rate error in the same way that the flux is computed from the count rate.

SB_SNR
The soft-band signal-to-noise ratio of the Chandra source.

SB_Exposure
The soft-band exposure time derived from the exposure map, in seconds (converted by the HEASARC from the ks units given in the original table).

SB_Counts
The aperture photometry counts in the soft band (0.5 - 2 keV) as derived from event data for each individual Obs_id and CCD where a source lands. Notice that this will not necessarily be equal to the product of the count rate and the exposure time. Circular extraction regions corresponding to the 90% ECF for that observation are centered on the source R.A. and Dec. The individual photometry values are then merged to produce a single set of values accounting for the ECF for each Obs_ID, given the different extraction regions needed.

SB_Counts_Error
The error in the soft-band (0.5 - 2 keV) aperture photometry net counts.

SB_AP_Exposure
The exposure time in the soft-band (0.5 - 2 keV) from the same region used to generate the aperture photometry, in seconds (converted by the HEASARC from the ks units given in the original table).

HB_Count_Rate
The count rate CR in the hard energy band (2 - 7 keV), in ct/s. These are effective count rates that would apply if the source had been observed at the aim point in every pointing, i.e., computed by dividing the best fit counts for the source by the effective exposure time at the position of the source (the effective exposure time includes corrections for vignetting, dither, bad pixels and spatially dependent quantum efficiency).

HB_Count_Rate_Error
The error in the count rate in the hard energy band (2 - 7 keV), in ct/s. The count rate error E(CR) at 68% confidence level was computed using the equation E(CR) == sqrt[C_(s,90%) + (1+a)B_90%]/0.9T, where C_s are the source counts estimated by EMLdetect, corrected to an area including 90% of the PSF, B are the background counts evaluated from the background rate (counts pixel-1) estimated by EMLdetect multiplied for an area of radius R_w, which is the mean of the radii, corresponding to 90% enclosed counts fraction (ECF) of each observation, weighted by the observation exposure relative to the total exposure, and T is the vignetting corrected exposure time at the position of the source from the exposure maps. The authors use a value of a = 0.5, to allow for uncertainties in the background, which is computed through the EMLdetect procedure: see Paper II, Puccetti et al. (2009, ApJS, submitted) for more details.

HB_Flux
The hard-band 2 - 10 keV flux of the Chandra source, in erg cm-2 s-1, computed converting count rates CR to fluxes F using the following formula: F = CR/(CF*1011), where CF is the energy conversion factor 0.381 counts erg-1 cm2) appropriate for a power-law spectrum with spectral index Gamma = 1.4 and Galactic column density N_H = 2.7 x 1020 cm-2. For sources not detected in this band, a 90% upper limit is reported (see Paper II for details). Notice that the energy ranges used for the hartd-band count rates and fluxes are different (2 - 7 keV versus 2 - 10 keV, respectively), as discussed in Section 2 of the reference paper.

HB_Flux_Error
The error in the hard-band 2 - 10 keV flux of the Chandra source, in erg cm-2 s-1, computed from the count rate error in the same way that the flux is computed from the count rate.

HB_SNR
The hard-band signal-to-noise ratio of the Chandra source.

HB_Exposure
The hard-band exposure time derived from the exposure map, in seconds (converted by the HEASARC from the ks units given in the original table).

HB_Counts
The aperture photometry counts in the hard band (2 - 7 keV) as derived from event data for each individual Obs_id and CCD where a source lands. Notice that this will not necessarily be equal to the product of the count rate and the exposure time. Circular extraction regions corresponding to the 90% ECF for that observation are centered on the source R.A. and Dec. The individual photometry values are then merged to produce a single set of values accounting for the ECF for each Obs_ID, given the different extraction regions needed.

HB_Counts_Error
The error in the hard-band (2 - 7 keV) aperture photometry net counts.

HB_AP_Exposure
The exposure time in the hard-band (2 - 7 keV) from the same region used to generate the aperture photometry, in seconds (converted by the HEASARC from the ks units given in the original table).

Hardness_Ratio
The hardness ratio of the Chandra source computed as follows: HR = (H-S)/(H+S), where H are the counts in the hard band and S the counts in the soft band. The hardness ratio was calculated starting with the EMLdetect rate values. Pseudo-source and background count values were generated using the net count rate, background rate (per pixel), and a 3 arcsecond source aperture and 5 - 20 arcsecond aperture for background areas. The aperture photometry was unsuitable for this purpose because the individual extraction apertures do not have the constant background/source area ratios required by the assumptions used in the Bayesian estimation of hradness ratio (BEHR) code.

Hardness_Ratio_Neg_Err
The 90% upper error in the hardness ratio of the Chandra source (calculated by the HEASARC from the 90% upper limit to the hardness ratio given in the original table). The upper and lower limits were calculated using the Bayesian estimation of hardness ratio code (BEHR; Park et al. 2006, ApJ, 652, 610).

Hardness_Ratio_Pos_Err
The 90% lower error in the hardness ratio of the Chandra source (calculated by the HEASARC from the 90% lower limit to the hardness ratio given in the original table). The upper and lower limits were calculated using the Bayesian estimation of hardness ratio code (BEHR; Park et al. 2006, ApJ, 652, 610).


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 13-Nov-2009