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LALABOOCXO - LALA Bootes Field Chandra X-Ray Point Source Catalog

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Overview

This table contains the results of an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha survey (LALA) Bootes field which was obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on board the Chandra X-Ray Observatory. This is one of the deepest Chandra images of the extragalactic sky, with only the 2 Ms Chandra Deep Field North (CDF-N) and the 1 Ms Chandra Deep Field South (CDF-S) observations being substantially deeper. In this table, the X-ray source catalog obtained from this image is presented, along with some results from an analysis of the X-ray source counts and optical identifications. The X-ray image is composed of two individual observations obtained in 2002 and reaches 0.5 - 2.0 and 2.0 - 10.0 keV flux limits of 1.5 x 10^-16 and 1.0 x 10^-15 ergs/cm^2/s, respectively, for point sources near the aim point. A total of 168 X-ray sources were detected: 160 in the 0.5 - 7.0 keV band, 132 in the 0.5 - 2.0 keV band, and 111 in the 2.0 - 7.0 keV band. Since X-ray source number 122 has two possible optical counterparts, it is listed twice, once for each counterpart, and the total number of entries in this table is this 169.

The primary optical data are R-band imaging from the NOAO Deep Wide-Field Survey (NDWFS), with a limiting magnitude of R = 25.7 magnitudes, (Vega, 3-sigma detection level, and a 4" diameter aperture). Optical counterparts within 1.5" or the 3-sigma X-ray positional uncertainties, whichever was larger, were detected above this level in the R band for 144 of the 168 X-ray sources. At least 90% of the optical counterparts should be the correct matches, and, at worst, there might be ~14 false matches.


Catalog Bibcode

2004AJ....127..213W

References

The 172 ks Chandra exposure of the LALA Bootes field: X-ray source catalog.
    Wang J.X., Malhotra S., Rhoads J.E., Brown M.J.I., Dey A., Heckman T.M.,
    Jannuzi B.T., Norman C.A., Tiede G.P., Tozzi P.
   <Astron. J., 127, 213-229 (2004)>
   =2004AJ....127..213W

Provenance

This table was created by the HEASARC in March 2007 based on the CDS table J/AJ/127/213 file table1.dat,

Parameters

Source_Number
A running number for the X-ray source which uniquely identifies the source.

Name
The IAU Name of the X-ray source using the 'CXOLALA1' prefix registered with the CDS Dictionary of Nomenclature of Celestial Objects and the truncated J2000.0 coordinates of the source (JHHMMSS.s-DDMMSS).

Alt_Name
An alternative name for the X-ray source recommended by the CDS Dictionary of Nomenclature of Celestial Objects using the prefix of '[WMR2004]' where WMR2004 stands for Wang, Malhotra and Rhoads, 2004), together with the source number.

RA
The Right Ascension of the X-ray source in the selected equinox. The RA was given in J2000.0 coordinates to a precision of 0.01 seconds of time in the original table. The positions were determined by wavdetect. Whenever possible, the authors used positions derived in the soft band, which has the best spatial resolution among the three bands. For sources which were not detected in the soft band, they used total band positions instead, if available, and hard-band positions were quoted for those sources detected only in the hard band.

Dec
The Declination of the X-ray source in the selected equinox. The Declination was given in J2000.0 coordinates to a precision of 0.1 arcseconds in the original table. The positions were determined by wavdetect. Whenever possible, the authors used positions derived in the soft band, which has the best spatial resolution among the three bands. For sources which were not detected in the soft band, they used total band positions instead, if available, and hard-band positions were quoted for those sources detected only in the hard band.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Error_Radius
The 3-sigma uncertainty of the centroid position as directly given by wavdetect, in arcseconds.

FB_Counts
The net counts in the total band (0.5 - 7 keV). The counts were calculated using circular aperture photometry. For each source, the authors defined a source region that was a circle centered at the source centroid position, with a radius R_s set to the 95% encircled-energy radius of the Chandra ACIS PSF. The value of R_s varied in the range of 2 - 15 arcseconds from the center to the edge of the field. Source photons were then extracted from the region, and the local background was extracted from an annulus with outer radius of 2.4 times R_s and an inner radius of 1.2 times R_s, after masking out nearby sources. The aperture correction (x 1/0.95) was applied to the source counts.

FB_Counts_Pos_Err
The upper 1-sigma Poisson uncertainty in the total-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

FB_Counts_Neg_Err
The lower 1-sigma Poisson uncertainty in the total-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

SB_Counts
The net counts in the soft band (0.5 - 2 keV). The counts were calculated using circular aperture photometry. For each source, the authors defined a source region that was a circle centered at the source centroid position, with a radius R_s set to the 95% encircled-energy radius of the Chandra ACIS PSF. The value of R_s varied in the range of 2 - 15 arcseconds from the center to the edge of the field. Source photons were then extracted from the region, and the local background was extracted from an annulus with outer radius of 2.4 times R_s and an inner radius of 1.2 times R_s, after masking out nearby sources. The aperture correction (x 1/0.95) was applied to the source counts.

SB_Counts_Pos_Err
The upper 1-sigma Poisson uncertainty in the soft-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

SB_Counts_Neg_Err
The lower 1-sigma Poisson uncertainty in the soft-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

HB_Counts
The net counts in the hard band (2 - 7 keV). The counts were calculated using circular aperture photometry. For each source, the authors defined a source region that was a circle centered at the source centroid position, with a radius R_s set to the 95% encircled-energy radius of the Chandra ACIS PSF. The value of R_s varied in the range of 2 - 15 arcseconds from the center to the edge of the field. Source photons were then extracted from the region, and the local background was extracted from an annulus with outer radius of 2.4 times R_s and an inner radius of 1.2 times R_s, after masking out nearby sources. The aperture correction (x 1/0.95) was applied to the source counts.

HB_Counts_Pos_Err
The upper 1-sigma Poisson uncertainty in the hard-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

HB_Counts_Neg_Err
The lower 1-sigma Poisson uncertainty in the hard-band net counts, calculated according to Gehrels (1986, ApJ, 303, 336).

Detection_Bands
An indication of the band(s) of the source detection. "T," "S," and "H" values mean sources detected in the total, soft, and hard bands, respectively. Multiple letters are used for sources detected in more than one band. For example, "TS" means detections in both the total band and the soft band, but nondetected in the hard band.

Hardness_Ratio
The hardness ratio defined as HR = (H - S)/(H + S), where H and S are the vignetting-corrected net counts in the hard and soft bands, respectively. The hardness ratios versus 0.5-10.0 keV band X-ray fluxes for the detected X-ray sources are plotted in Figure 2 of the reference paper. Assuming a power-law spectrum with the Galactic H I column density (1.15 x 10^20 cm^-2), the observed hardness ratio can be converted to the photon index Gamma of the spectrum, which is also presented in the figure. As presented in earlier surveys, harder sources are seen at fainter fluxes, most of which are believed to be obscured AGNs.

Hardness_Ratio_Pos_Err
The upper 1-sigma Poisson uncertainty in the hardness ratio.

Hardness_Ratio_Neg_Err
The lower 1-sigma Poisson uncertainty in the hardness ratio.

FB_Flux
The X-ray flux (Galactic absorption-corrected) in the 0.5 - 10.0 keV band, in units of ergs cm^-2 s^-1. A power-law spectrum with the Galactic column density was assumed in order to calculate the conversion factor from net counts to X-ray flux. The photon index of the power-law was chosen at Gamma = 1.4. Three-band net count rates were calculated by dividing the net counts on the total, soft and hard bands by the effective exposure time (calculated by multiplying 172 ks by the ratio of the exposure map at the aim point to the value of the exposure map averaged within the extraction region for each source, and done in each band separately) at each source position in each band, and then converted into X-ray fluxes in the 0.5-10.0, 0.5-2.0, and 2.0-10.0 keV bands, respectively. These settings make the results directly comparable with those from other surveys. The conversion factors used were 1.25 x 10^-11 ergs cm^-2 count^-1 from the 0.5-7.0 keV band observed count rate to the Galactic absorption-corrected X-ray flux in the 0.5-10.0 keV band, 4.67 x 10^-12 ergs cm^-2 count^-1 from the 0.5-2.0 keV band count rate to the 0.5-2.0 keV band flux, and 2.96 x 10^-11 ergs cm^-2 count^-1 from the 2.0-7.0 keV band count rate to the 2.0-10.0 keV band flux. Note that the total band (0.5-10.0 keV) flux is not equal to the sum of the soft- and hard-band fluxes if the actual photon index differs from 1.4.

SB_Flux_Limit
If this parameter has a value of '<', the corresponding flux is an upper limit.

SB_Flux
The X-ray flux (Galactic absorption-corrected) in the 0.5 - 2.0 keV band, in units of ergs cm^-2 s^-1. A power-law spectrum with the Galactic column density was assumed in order to calculate the conversion factor from net counts to X-ray flux. The photon index of the power-law was chosen at Gamma = 1.4. Three-band net count rates were calculated by dividing the net counts on the total, soft and hard bands by the effective exposure time (calculated by multiplying 172 ks by the ratio of the exposure map at the aim point to the value of the exposure map averaged within the extraction region for each source, and done in each band separately) at each source position in each band, and then converted into X-ray fluxes in the 0.5-10.0, 0.5-2.0, and 2.0-10.0 keV bands, respectively. These settings make the results directly comparable with those from other surveys. The conversion factors used were 1.25 x 10^-11 ergs cm^-2 count^-1 from the 0.5-7.0 keV band observed count rate to the Galactic absorption-corrected X-ray flux in the 0.5-10.0 keV band, 4.67 x 10^-12 ergs cm^-2 count^-1 from the 0.5-2.0 keV band count rate to the 0.5-2.0 keV band flux, and 2.96 x 10^-11 ergs cm^-2 count^-1 from the 2.0-7.0 keV band count rate to the 2.0-10.0 keV band flux. Note that the total band (0.5-10.0 keV) flux is not equal to the sum of the soft- and hard-band fluxes if the actual photon index differs from 1.4.

HB_Flux_Limit
If this parameter has a value of '<', the corresponding flux is an upper limit.

HB_Flux
The X-ray flux (Galactic absorption-corrected) in the 2.0 - 10.0 keV band, in units of ergs cm^-2 s^-1. A power-law spectrum with the Galactic column density was assumed in order to calculate the conversion factor from net counts to X-ray flux. The photon index of the power-law was chosen at Gamma = 1.4. Three-band net count rates were calculated by dividing the net counts on the total, soft and hard bands by the effective exposure time (calculated by multiplying 172 ks by the ratio of the exposure map at the aim point to the value of the exposure map averaged within the extraction region for each source, and done in each band separately) at each source position in each band, and then converted into X-ray fluxes in the 0.5-10.0, 0.5-2.0, and 2.0-10.0 keV bands, respectively. These settings make the results directly comparable with those from other surveys. The conversion factors used were 1.25 x 10^-11 ergs cm^-2 count^-1 from the 0.5-7.0 keV band observed count rate to the Galactic absorption-corrected X-ray flux in the 0.5-10.0 keV band, 4.67 x 10^-12 ergs cm^-2 count^-1 from the 0.5-2.0 keV band count rate to the 0.5-2.0 keV band flux, and 2.96 x 10^-11 ergs cm^-2 count^-1 from the 2.0-7.0 keV band count rate to the 2.0-10.0 keV band flux. Note that the total band (0.5-10.0 keV) flux is not equal to the sum of the soft- and hard-band fluxes if the actual photon index differs from 1.4.

RA_Offset
The offset of the detected optical counterpart from the X-ray source positions in the Right Ascension direction, in the sense of optical - X-ray position, in arcseconds.

Dec_Offset
The offset of the detected optical counterpart from the X-ray source positions in the Declination direction, in the sense of optical - X-ray position, in arcseconds.

Rmag_Limit
This parameter is set to '>' to indicate that the source was not detected in th R band and that the quoted value is the 3-sigma limit to the R-band magnitude.

Rmag
The R-band AUTO magnitude (the Kron-like elliptical aperture magnitude: see Bertin & Arnouts, 1996A&AS..117..393B) of the optical counterpart to the X-ray source.

Rmag_Error
The 1-sigma uncertainty in the R-band magnitude, as directly outputted from SExtractor, i.e., without including the uncertainty of the R-band zero point.

Rmag_Flag
This parameter contains flags on the quoted R-band magnitude for a few of the sources, as follows:

       a: Source No. 22 is overlapped by bleeding of charge in the NDWFS R
          image we used in this paper. Source position and R band magnitude
          were measured from an older version of the NDWFS R image.
       b: Source No. 37 and 160 are overlapped by bleeding of charge in both
          the NDWFS R and the older NDWFS R images.
  

Opt_Ctrprt_FWHM
The Full-Width Half-Maximum (FWHM) of the optical counterpart of the X-ray source in the NOAO Deep Wide-Field Survey (NDWFS) R-band image.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 26-Mar-2007