CHANSEXOID: Help

Overview

This table which combines data presented in Eckart et al. (2005, 2006) has links to the list of SEXSI X-ray sources (the HEASARC Browse table CHANSEXSI: see Paper I = Harrison et al. 2003, ApJ, 596, 944).

Catalog Bibcodes

References

The serendipitous extragalactic X-ray source identification (SEXSI) program.
II. Optical imaging.
    Eckart M.E., Laird E.S., Stern D., Mao P.H., Helfand D.J., Harrison F.A.
   <Astrophys. J. Suppl. Ser., 156, 35-45 (2005)>
   =2005ApJS..156...35E    (SIMBAD/NED BibCode)

III.Optical spectroscopy.
    Eckart M.E., Stern D., Helfand D.J., Harrison F.A., Mao P.H., Yost S.A.
   <Astrophys. J. Suppl. Ser., 165, 19-56 (2006)>
   =2006ApJS..165...19E    (SIMBAD/NED BibCode)

Provenance

Parameters

Name
The name of the SEXSI X-ray source in the standard truncated J2000 equatorial coordinate-based format using the IAU-registered CXOSEXSI prefix: i.e., "CXOSEXSI JHHMMSS.s+DDMMSS".

RA
The Right Ascension of the X-ray source in the selected equinox. The RA was given in J2000 equatorial coordinates and to a precision of 0.01 seconds of time in the originating table. The X-ray source positions have been corrected for the mean optical to X-ray offsets. Note that since the source names, which are identical to those in Paper I and the HEASARC's CHANSEXSI table, are derived from the hard-band X-ray images, these refined positions will not exactly match the positions encoded in the names, although the mean offsets are typically less than 1 arcsecond.

Dec
The Declination of the X-ray source in the selected equinox. The Dec was given in J2000 equatorial coordinates and to a precision of 0.1 arcseconds in the originating table. The X-ray source positions have been corrected for the mean optical to X-ray offsets. Note that since the source names, which are identical to those in Paper I and the HEASARC's CHANSEXSI table, are derived from the hard-band X-ray images, these refined positions will not exactly match the positions encoded in the names, although the mean offsets are typically less than 1 arcsecond.

LII
The Galactic Longitude of the X-ray source.

BII
The Galactic Latitude of the X-ray source.

Off_Axis_Angle
The off-axis angle of the X-ray source, in arcminutes, i.e., the angular distance of the source position from the telescope aim point.

HB_Flux
The unabsorbed hard-band (2.0 - 10 keV) flux of the X-ray source, in units of erg/cm^2/s, converted from counts assuming an intrinsic power-law spectrum with a photon index Gamma of 1.5, and corrected for Galactic absorption.

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

Hardness_Ratio
The hardness ratio of the X-ray source, HR=(H-S)/(H+S), where H is the corrected counts in the 2.0-10 keV band and S is the corrected counts in the 0.5-2.0 keV band extracted at the position of the hard-band detection. Note that this last feature is different from the procedure adopted in Paper I, where if there was not a significant soft-band source detected, the hardness ratio was set to 1.0.

Hardness_Ratio_Flag
For a subset of cases where the soft-band counts recorded at the hard-band source position were less than twice the soft-band background counts, the hardness ratio is considered a lower limit and (i) this flag parameter has been set to 1 and (ii) the hardness ratio has been set to HR = (H-S_limit)/(H+S_limit), where S_limit is 2 x soft-band backround counts. For cases where the hardness ratio is solid, i.e., not a limit, this flag parameter is set to 0.

Cluster_Flag
This parameter is a flag which indicates whether or not the source is a potential member of a target cluster, and is defined as follows:

  1 means that the source falls within 1 comoving Mpc of the known target
    cluster center and thus is a potential cluster member
  0 means that the source does not fall within 1 comoving Mpc of the target
    cluster center
  

Optical_Id_Flag
This parameter contains the optical identification flag as given in Table 2 of Paper III, which is defined as follows:

  6 = no optical counterpart, but the location is contaminated by nearby bright
      source (limiting mag will be incorrect)
  5 = more than one optical source in X-ray error circle, the source with
      the smallest positional offset is recorded in the table
  4 = solid ID, but the R-band magnitude is affected by a nearby bright source
  3 = source saturated in the SEXIS optical image, the R-band magnitude is
      taken from the Guide Star Catalog II or a secondary source in Vizier
  2 = no optical counterpart, the listed magnitude is a lower limit
  1 = solid optical identification
  0 = no optical coverage
  

Rc_Mag
The Cousins R-band magnitude of the optical counterpart. Note that special attention must be paid to the optical_id_flag parameter value when interpreting the rc_mag parameter value: for example, if the former has a value of 2 (optical counterpart not detected), then the latter is a limit to the actual rc_mag value.

Rc_Mag_Error
The error in the R-band magnitude.

Image_Limit_Rc_Mag
The limiting R-band magnitude for the image from which the optical counterpart, or a lower limit thereto, was derived.

Rc_Mag_Flag
This flag parameter is set to 1 if Rc_mag > (fainter than) the limiting R-band magnitude for the image, else it is set to 0.

Offset_RA
The difference between the RA of the X-ray source and that of the optical counterpart, RA_X - RA_opt, in arcseconds, where RA_X is the astrometrically-corrected RA of the X-ray source.

Offset_Dec
The difference between the Declination of the X-ray source and that of the optical counterpart, Dec_X - Dec_opt, in arcseconds, where Dec_X is the astrometrically-corrected Declination of the X-ray source.

Offset_Total
The total positional difference between the optical counterpart and the astrometrically-corrected X-ray source position, in arcseconds.

Log_Fx_Fopt
The logarithmic X-ray to optical flux ratio as given by the relation log (f_x/f_opt) = log f_x + (Rc_mag/2.5) + 5.50, derived from the Kron-Cousins R-band filter transmission function. Note that special attention must be paid to the optical_id_flag parameter value when interpreting the log_fx_fopt parameter value: for example, if the former has a value of 2 (optical counterpart not detected), then the latter is a limit to the actual log_fx_fopt value.

Stellarity
The SExtractor CLASS_STAR parameter value for basic star-galaxy separation, i.e., the stellarity fraction, with possible values ranging from 0.0 for significantly extended sources to 1.0 for sources consistent with perfectly stellar PSFs. The stellarity value of the 8 bright sources with values of optical_id_flag = 3 is set to 1.00. The stellarity data are presented with the caveat that the values should only be used for broad separation, for example of sources near 0 versus 1, but not for detailed quantitative analysis.

Redshift
The redshift of the optical counterpart to the X-ray source, determined as described in Section 4 of Eckart et al. (2006, Paper III).

Object_Type
The optical counterpart classification (see Section 4 of Paper III for details on the class definitions):

     ALG = absorption-line galaxy
     ELG = emission-line galaxy
   BLAGN = broad-lined AGN
   NLAGN = narrow-line AGN
    star = any type of star
  

Spectral_Notes
This parameter contains flags for notes on the spectra of individual sources which have the following values:

  a = Optical counterpart falls just outside the strict search area
      (see Section 5 and Table 3 of Paper III).
  b = Identification from the Guide Star Catalog II, McLean et al. (2000)
      or VIZIER database.
  c = Identification from the Einstein Observatory Extended
      Medium-Sensitivity Survey, Stocke et al.(1991), object MS1214.3+3811.
  d = Cataclysmic variable, spectrum shows 274 km/s blueshift.
  e = Member of (non-target) nearby galaxy, NGC 5879, which happened to be
      in the Chandra pointing of SEXSI field QSO 1508. The 3 2-10 keV sources
      spectroscopically confirmed to be associated with NGC 5879 are flagged.
  f = This object was identified using its 2-D spectrum as it could not be
      easily extracted to form a 1-D spectrum; the observable wavelength
      range is thus omitted.
  g = In Paper II this source had optical_id_flag=5 (which means >1 optical
      source in the search area).  The spectrum shows a BLAGN, thus the authors
      changed the source to optical_id_flag=1, meaning that there is a secure
      optical counterpart identification.
  h = Confirmed target cluster member (spectroscopically confiremd within 1 Mpc
      of target cluster center). In Papers I and II sources were flagged as
      being potentially within 1 Mpc of the target cluster center as determined
      by their position in the image (and ignored for the log N - log S
      calculation). Now that redshift information is available, only sources at
      the target cluster redshift remain flagged. See Section 11 of Paper III
      for details on these sources.
  i = Confirmed (non-target) group/cluster detected in Holden et al. 2002
      (see Section 11 of Paper III).
  j = Possible BALQSO.
  k = Line identification or redshift tentative.
  l = This source spectrum shows two ELGs, one at z=0.426, one at z=1.432.
      The nearer source matches the R=22.25 in the photometry, but the
      fainter z=1.432 source, undetected in the photometry, also appears in
      the error circle. This source is thus eliminated from the analysis.
  m = J145215.6+430448: a low-ionization, broad absorption line quasar.
  n = Spectrum has gap of > 100 Angstrom between red and blue side.
  

Log_Lx
The log of the absorbed rest-frame hard-band (2.0 - 10 keV) luminosity, in erg/s. calculated from the hard-band flux and the redshift, assuming that the source has an X-ray photon index of 1.5. The authors use the standard cosmology Omega_m=0.3, Omega_lambda=0.7, and a Hubble Constant of 65 km/s/Mpc to calculate the luminosity distance.

Log_NH_Flag
This parameter contains a flag for the corresponding log_nh value, as follows:

  S = Source detected on off-axis ACIS-S chip (2-3) and thus nH is calculated
      from the hardness ratio, not a spectral fit. See Section 5 of Paper III.
  < = When a nH measurement is zero, the authors report '<' in the
      corresponding flag column.
  > = nH is a lower limit (occurs when the hardness ratio is a lower limit and
      nH is derived from the hardness ratio).
  H = Bad XSPEC fit. nH is calculated from hardness ratio, not a spectral fit.
  

Log_NH
The log of the neutral hydrogen column density, log nH, in cm^-2 as determined by X-ray spectral fitting of each source using XSPEC. Since many sources have a low number of counts, the fits were performed assuming an intrinsic power-law spectrum with a fixed photon index Gamma = 1.9 typical of AGN continua, and the Galactic column density at z = 0.0, and only the intrinsic column density at the source redshift was allowed to vary. When an nH measurement is zero, the authors report '<' for the corresponding flag value.

Log_NH_Lower_Flag
This parameter contains a flag for the corresponding log_nh_lower value, as follows:

  S = Source detected on off-axis ACIS-S chip (2-3) and thus nH is calculated
      from the hardness ratio, not a spectral fit. See Section 5 of Paper III.
  < = When a nH measurement is zero, the authors report '<' in the
      corresponding flag column.
  > = nH is a lower limit (occurs when the hardness ratio is a lower limit and
      nH is derived from the hardness ratio).
  H = Bad XSPEC fit. nH is calculated from hardness ratio, not a spectral fit.
  

Log_NH_Lower
The 1-sigma lower limit to the value of log nH, as derived from the spectral fit. When an nH measurement is zero, the authors report '<' for the corresponding flag value.

Log_NH_Upper_Flag
This parameter contains a flag for the corresponding log_nh_upper value, as follows:

  S = Source detected on off-axis ACIS-S chip (2-3) and thus nH is calculated
      from the hardness ratio, not a spectral fit. See Section 5 of Paper III.
  < = When a nH measurement is zero, the authors report '<' in the
      corresponding flag column.
  > = nH is a lower limit (occurs when the hardness ratio is a lower limit and
      nH is derived from the hardness ratio).
  H = Bad XSPEC fit. nH is calculated from hardness ratio, not a spectral fit.
  

Log_NH_Upper
The 1-sigma upper limit to the value of log nH, as derived from the spectral fit. When an nH measurement is zero, the authors report '<' for the corresponding flag value.

Lower_Rf_Wavelength
The lower limit of the optical spectral wavelength range, in Angstroms, shifted to the rest frame of the object if the redshift is known; when a a source spectrum shows continuum only, and no redshift has been determined, the wavelength range limits are reported in the observed frame.

Upper_Rf_Wavelength
The higher limit of the optical spectral wavelength range, in Angstroms, shifted to the rest frame of the object if the redshift is known; when a a source spectrum shows continuum only, and no redshift has been determined, the wavelength range limits are reported in the observed frame.

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