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CLASXS - Chandra Large-Area Synoptic X-Ray Survey of Lockman Hole-NW

HEASARC
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Overview

This table contains the X-ray catalog and basic results from the wide-area, moderately deep Chandra Large Area Synoptic X-ray Survey (CLASXS) of the Lockman Hole-Northwest (LHNW) field (Yang et al. 2004), as well as the results from optical and near-infrared photometric and spectroscopic observations of these X-ray sources (Steffen et al. 2004).

The nine ACIS-I fields cover a contiguous solid angle of 0.4 square degrees and reach fluxes of 5 x 10-16 ergs/cm2/s (0.4 - 2 keV) and 3 x 10^-15 ergs/cm2/s (2 - 8 keV). (Note that fields LHNW 1-3 were observed during 2001 April 30-May 17, and that the rest of the fields were observed during 2002 April 29-May 4). This survey bridges the gap between ultradeep pencil-beam surveys, such as the Chandra Deep Fields (CDFs), and shallower, large-area surveys, allowing a better probe of the X-ray sources that contribute most of the 2 - 10 keV cosmic X-ray background (CXB). A total of 525 X-ray point sources and four extended sources were found.

There are B, V, R, I, and z' photometry for 521 (99%) of the 525 sources in the X-ray catalog and spectroscopic redshifts for 271 (52%), including 20 stars. The authors did not find evidence for redshift groupings of the X-ray sources, like those found in the Chandra Deep Field surveys, because of the larger solid angle covered by this survey. They separated the X-ray sources by optical spectral type and examined the colors, apparent and absolute magnitudes, and redshift distributions for the broad-line and non-broad-line active galactic nuclei. Combining their wide-area survey with other Chandra and XMM-Newton hard X-ray surveys, they find a definite lack of luminous, high accretion rate sources at z < 1, consistent with previous observations that showed that supermassive black hole growth is dominated at low redshifts by sources with low accretion rates.


Catalog Bibcodes

2004AJ....128.1501Y
2004AJ....128.1483S

References

The Chandra Large Area Synoptic X-ray Survey (CLASXS) of the
Lockman Hole-Northwest: the X-ray catalog.
    Yang Y., Mushotzky R.F., Steffen A.T., Barger A.J., Cowie L.L.
   <Astron. J., 128, 1501-1523 (2004)>
   =2004AJ....128.1501Y    (SIMBAD/NED BibCode)

An optical catalog of the Chandra Large Area Synoptic X-ray Survey sources.
    Steffen A.T., Barger A.J., Capak P., Cowie L.L., Mushotzky R.F., Yang Y.
   <Astron. J., 128, 1483-1500 (2004)>
   =2004AJ....128.1483S    (SIMBAD/NED BibCode)

Provenance

This table was created by the HEASARC in May 2005 from the merger of 3 CDS tables, corresponding to Tables 2 and 3 from Yang et al. 2005 and Table 1 of Steffen et al. (2005):

               J/AJ/128/1501/table2.dat
               J/AJ/128/1501/table3.dat
               J/AJ/128/1483/table1.dat

Parameters

Source_Number
The Yang et al. (2004) source identification number, a unique identifier in ascending order of J2000 Right Ascension.

Name
The recommended CLASXS source designation, based on the X-ray source identification number.

RA
The Right Ascension of the X-ray source in the selected equinox. This was given in J2000 equatorial coordinates and to a precision of 0.01 seconds of time in the original table. The X-ray position has been corrected for the aspect errors of the telescope, if applicable, and for the general astrometric solution by comparing with the optical images. For sources with multiple detections in the 3 bands and the 9 observations, the best position is taken.

Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 equatorial coordinates and to a precision of 0.1 arcseconds in the original table. The X-ray position has been corrected for the aspect errors of the telescope, if applicable, and for the general astrometric solution by comparing with the optical images. For sources with multiple detections in the 3 bands and the 9 observations, the best position is taken.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

RA_Error
The statistical uncertainty in the Right Ascension of the X-ray source, in arcseconds, quoted from the wavdetect lists.

Dec_Error
The statistical uncertainty in the Declination of the X-ray source, in arcseconds, quoted from the wavdetect lists.

Limit_SB_Flux
This parameter is set to '<' if the quoted flux in this band is an upper limit rather than a detection.

SB_Flux
The X-ray flux in the soft band (0.4 - 2.0 keV), in units of erg/s/cm2. The X-ray flux has been calculated from the observed X-ray counts using an individual power-law index based on the hardness ratio, i.e., the ratio of the observed hard to soft X-ray counts. If a source is detected in multiple observations and if there is more than one observation in which the source effective area is more than 80% of the effective area at the aim point, then the mean flux is used; otherwise, the flux from the observation that has the largest effective area is used.

SB_Flux_Pos_Err
The upper 1-sigma Poisson error in the soft band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

SB_Flux_Neg_Err
The lower 1-sigma Poisson error in the soft band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

Limit_HB_Flux
This parameter is set to '<' if the quoted flux in this band is an upper limit rather than a detection.

HB_Flux
The X-ray flux in the hard band (2 - 8 keV), in units of erg/s/cm2. The X-ray flux has been calculated from the observed X-ray counts using an individual power-law index based on the hardness ratio, i.e., the ratio of the observed hard to soft X-ray counts. If a source is detected in multiple observations and if there is more than one observation in which the source effective area is more than 80% of the effective area at the aim point, then the mean flux is used; otherwise, the flux from the observation that has the largest effective area is used.

HB_Flux_Pos_Err
The upper 1-sigma Poisson error in the hard band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

HB_Flux_Neg_Err
The lower 1-sigma Poisson error in the hard band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

Limit_FB_Flux
This parameter is set to '<' if the quoted flux in this band is an upper limit rather than a detection.

FB_Flux
The X-ray flux in the full band (0.4 - 8.0 keV), in units of erg/s/cm2. The X-ray flux has been calculated from the observed X-ray counts using an individual power-law index based on the hardness ratio, i.e., the ratio of the observed hard to soft X-ray counts. If a source is detected in multiple observations and if there is more than one observation in which the source effective area is more than 80% of the effective area at the aim point, then the mean flux is used; otherwise, the flux from the observation that has the largest effective area is used.

FB_Flux_Pos_Err
The upper 1-sigma Poisson error in the full band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

FB_Flux_Neg_Err
The lower 1-sigma Poisson error in the full band flux, in units of erg/s/cm2. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted flux could be negative. In this case, only the upper Poisson error is quoted.

Limit_Hardness_Ratio
This parameter is set to '<' or '>' if the quoted hardness ratio (HR) band is an upper (or lower) limit.

Hardness_Ratio
The hardness ratio (HR) defined as HR=C_Hard/C_Soft, where C_Hard and C_Soft are the count rates in the hard and soft bands, respectively.

Limit_SB_Counts
This parameter is set to '<' if the quoted counts in this band correspond to an upper limit rather than a detection.

SB_Counts
The net counts in the soft band (0.4 - 2.0 keV). If a source is detected in multiple observations, then the observation in which the source has the largest effective area is used (the observation used is specified by the value of the best_field_num parameter). As for the fluxes, for the sources with negative counts, only the upper limits are listed.

SB_Counts_Pos_Err
The upper 1-sigma Poisson error in the soft band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

SB_Counts_Neg_Err
The lower 1-sigma Poisson error in the soft band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

Limit_HB_Counts
This parameter is set to '<' if the quoted counts in this band correspond to an upper limit rather than a detection.

HB_Counts
The net counts in the hard band (2.0 - 8.0 keV). If a source is detected in multiple observations, then the observation in which the source has the largest effective area is used (the observation used is specified by the value of the best_field_num parameter. As for the fluxes, for the sources with negative counts, only the upper limits are listed.

HB_Counts_Pos_Err
The upper 1-sigma Poisson error in the hard band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

HB_Counts_Neg_Err
The lower 1-sigma Poisson error in the hard band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

Limit_FB_Counts
This parameter is set to '<' if the quoted counts in this band correspond to an upper limit rather than a detection.

FB_Counts
The net counts in the full band (0.4 - 8.0 keV). If a source is detected in multiple observations, then the observation in which the source has the largest effective area is used (the observation used is specified by the value of the best_field_num parameter. As for the fluxes, for the sources with negative counts, only the upper limits are listed.

FB_Counts_Pos_Err
The upper 1-sigma Poisson error in the full band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

FB_Counts_Neg_Err
The lower 1-sigma Poisson error in the full band counts. The errors quoted are calculated using the approximations from Gehrels (1986ApJ...303..336G). For any source detected in one band but with a very weak signal in another, the background-subtracted counts could be negative. In this case, only the upper Poisson error is quoted.

SB_Exposure
The effective exposure time, in seconds, in the soft band (0.4 - 2.0 keV).

HB_Exposure
The effective exposure time, in seconds, in the hard band (2.0 - 8.0 keV).

FB_Exposure
The effective exposure time, in seconds, in the full band (0.4 - 8.0 keV).

Best_Field_Num
The LHNW field number for which the source has the largest effective area.

Num_Fields_Det
The LHNW field number(s), where each digit represents a field number, in which the source has been detected in at least one of the three bands. Sources with multiple detections are necessary for the detection of variability.

RA_Optical
The Right Ascension of the optical counterpart, in fixed (J2000) sexagesimal coordinates. This was given in J2000 decimal degrees to a precision of 1 microdegrees in the original table.

Dec_Optical
The Declination of the optical counterpart, in fixed (J2000) sexagesimal coordinates. This was given in J2000 decimal degrees to a precision of 10 microdegrees in the original table.

Off_Axis_Angle
The (smallest) radial distance of the source from the aim point among the LHNW fields in which it was detected, in arcminutes.

SB2_Flux
The modified (0.5 - 2 keV) soft-band X-ray flux, in erg/s/cm2, as quoted in the Steffen et al. (2004) Table 1. As opposed to the (0.4 - 2.0 keV) soft band flux (quoted in Yang et al. (2004) and given in this table as the sb_flux parameter, q.v.), this flux has been calculated for all sources using the same power-law spectral energy distribution, viz., one having a photon index of 1.8 and a column density of 5.7 x 10^19 atoms cm-2.

Limit_Bmag
This parameter is set to '>' to indicate that the quoted magnitude is an upper (bright) limit not a measurement.

Bmag
The aperture-corrected magnitude m(B) in the Johnson B-band in the AB magnitude system where m_AB = -2.5log f_nu - 48.60, and f_nu is the flux of the source in units of erg/s/cm2/Hz.

Limit_Vmag
This parameter is set to '>' to indicate that the quoted magnitude is an upper (bright) limit not a measurement.

Vmag
The aperture-corrected magnitude m(V) in the Johnson V-band in the AB magnitude system where m_AB = -2.5log f_nu - 48.60, and f_nu is the flux of the source in units of erg/s/cm2/Hz.

Limit_Rc_Mag
This parameter is set to '>' to indicate that the quoted magnitude is an upper (bright) limit not a measurement.

Rc_Mag
The aperture-corrected magnitude m(Rc) in the Cousins R-band in the AB magnitude system where m_AB = -2.5log f_nu - 48.60, and f_nu is the flux of the source in units of erg/s/cm2/Hz.

Limit_Ic_Mag
This parameter is set to '>' to indicate that the quoted magnitude is an upper (bright) limit not a measurement.

Ic_Mag
The aperture-corrected magnitude m(Ic) in the Cousins I-band in the AB magnitude system where m_AB = -2.5log f_nu - 48.60, and f_nu is the flux of the source in units of erg/s/cm2/Hz.

Limit_Zd_Mag
This parameter is set to '>' to indicate that the quoted magnitude is an upper (bright) limit not a measurement.

Zd_Mag
The aperture-corrected magnitude m(z') in the Sloan z'-band in the AB magnitude system where m_AB = -2.5log f_nu - 48.60, and f_nu is the flux of the source in units of erg/s/cm2/Hz.

Redshift
The spectroscopic redshift of the optical counterpart to the X-ray source.

Redshift_Flag
This parameter flags information about the spectroscopic redshift coded as follows:

     -2 = Star;
     -1 = Unobserved;
      0 = Absorption-line system;
      1 = Star-former;
      2 = Seyfert 2 based on strong [O II] relative to H{beta} or strong [Ne III]
          relative to [O II];
      3 = Seyfert 2 with [Ne V] or C IV in emission;
      4 = Broad-line AGN (FWHM>1000km/s).
  

Alt_Name
An alternative CLASXS source designation, based on the J2000 X-ray source position and the prefix of 'CXCCLASXS,' as suggested by the authors for these X-ray sources.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 27-Jan-2009