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GALEXTDSC - GALEX Time Domain Survey Catalog

HEASARC
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Overview

This table contains results from the selection and classification of over a thousand ultraviolet (UV) variable sources discovered in ~ 40 deg2 of GALEX Time Domain Survey (TDS) NUV images observed with a cadence of 2 days and a baseline of observations of ~ 3 years. The GALEX TDS fields were designed to be in spatial and temporal coordination with the Pan-STARRS1 Medium Deep Survey, which provides deep optical imaging and simultaneous optical transient detections via image differencing. The authors characterize the GALEX photometric errors empirically as a function of mean magnitude, and select sources that vary at the 5-sigma level in at least one epoch. They measure the statistical properties of the UV variability, including the structure function on timescales of days and years, and report classifications for the GALEX TDS sample using a combination of optical host colors and morphology, UV light curve characteristics, and matches to archival X-ray, and spectroscopy catalogs.

The authors classify 62% of the sources as active galaxies (358 quasars and 305 active galactic nuclei), and 10% as variable stars (including 37 RR Lyrae, 53 M dwarf flare stars, and 2 cataclysmic variables). They detect a large-amplitude tail in the UV variability distribution for M-dwarf flare stars and RR Lyrae, reaching up to |Delta-M| = 4.6 and 2.9 magnitudes, respectively. The mean amplitude of the structure function for quasars on year timescales is five times larger than observed at optical wavelengths. The remaining unclassified sources include UV-bright extragalactic transients, two of which have been spectroscopically confirmed to be a young core-collapse supernova and a flare from the tidal disruption of a star by a dormant super-massive black hole. The authors calculate a surface density for variable sources in the UV with NUV < 23 mag and |Delta-M| > 0.2 mag of ~ 8.0, 7.7, and 1.8 deg-2 for quasars, AGN, and RR Lyrae stars, respectively, and a surface density rate in the UV for transient sources, using the effective survey time at the cadence appropriate to each class, of ~15 and 52 deg-2 yr-1 for M dwarfs and extragalactic transients, respectively.

The GALEX observations were made using the NUV detector which has an 1.25 degree diameter field of view and an effective wavelength of 2316 Angstroms. During the window of observing visibility of each GALEX TDS field (from two to four weeks, one to two times per year), they were observed with a cadence of 2 days, and a typical exposure time per epoch of 1.5 ks (or a 5-sigma point-source limit of mAB(NUV) ~ 23.3 magnitude), with a range from 1.0 to 1.7 ks. Table 2 in the reference paper lists the RA and Dec of their centers, the Galactic extinction E(B - V ) for each field from the Schlegel et al. (1998, ApJ, 500, 525) dust maps, and the number of epochs per field.


Catalog Bibcode

2013ApJ...766...60G

References

The GALEX Time Domain Survey. I. Selection and Classification of Over a
Thousand Ultraviolet Variable Sources
     Gezari S., Martin D.C., Forster K., Neill J.D., Huber M., Heckman T.,
     Bianchi L., Morrissey P., Neff S.G., Seibert M., Schiminovich D.,
     Wyder T.K., Burgett W.S., Chambers K.C., Kaiser N., Magnier E.A.,
     Price P.A., Tonry J.L.
     <Astrophys. J., 766, 60 (2013)>
     =2013ApJ...766...60G

Provenance

This table was created by the HEASARC in May 2013 based on a machine-readable version of Table 4 from the paper which was obtained from the ApJ web site.

Parameters

Name
The GALEX TDS designation of the ultraviolet variable source, e.g., 'CDFS_MOS00-03' where the string preceding the hyphen is the GALEX TDS field identifier (the properties of these fields including the positions of their centers are listed in Table 2 of the reference paper where an additional prefix 'PS_' for Pan-STARRS is used) and the part after the hyphen is a unique (for the specific field) source number. Thus, the sample source above is source number 3 in the PS_CDFS_MOS00 field.

RA
The Right Ascension of the ultraviolet variable source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-4 degrees (0.36 arcseconds) in the original table.

Dec
The Declination of the ultraviolet variable source in the selected equinox. This was given in J2000 decimal degrees to a precision of 10-4 degrees (0.36 arcseconds) in the original table.

LII
The Galactic Longitude of the ultraviolet variable source.

BII
The Galactic Latitude of the ultraviolet variable source.

NUV_Mag_Low_Limit
This flag parameter is set to '>' if the corresponding parameter value is a lower limit.

NUV_Mag_Low
The NUV AB magnitude (corrected for Galactic extinction as described in the Overview above) of the ultraviolet variable source when in the low state.

Max_Delta_NUV_Mag_Limit
This flag parameter is set to '>' if the corresponding parameter value is a lower limit.

Max_Delta_NUV_Mag
The maximum amplitude of the NUV variability, |Delta-m_max_|, of the ultraviolet variable source, in magnitudes.

Sigma_NUV_Mag_Limit
This flag parameter is set to '<' if the corresponding parameter value is an upper limit.

Sigma_NUV_Mag
The intrinsic variability, sigmaint , of the ultraviolet variable source, in magnitudes, calculated as described in Section 3.2 of the reference paper.

SF_Days_Limit
This flag parameter is set to '<' if the corresponding parameter value is an upper limit.

SF_Days
The structure function, Sd, of the ultraviolet variable source on a timescale of days. This is defined in Section 3.2 of the reference paper as the maximum value of the structure function evaluated for characteristic timescale bins of 2 +/- 0.5, 4 +/- 0.5, 6 +/- 0.5 and 8 +/- 0.5 days.

SF_Years_Limit
This flag parameter is set to '<' if the corresponding parameter value is an upper limit.

SF_Years
The structure function, Syr, of the ultraviolet variable source on a timescale of years. This is defined in Section 3.2 of the reference paper as the maximum value of the structure function evaluated for characteristic timescale bins of 0.96 +/- 0.14 and 1.96 +/- 0.04 years.

Var_Type
The characteristics of the NUV light curve, as follows:

      V = stochastic variability;
      F = indicates flaring variability.
  

Host_Morphology
The morphology of the matching optical host, as follows:

     pt = point source;
    ext = extended source.
  

Host_Rmag
The r-band AB magnitude (corrected for Galactic extinction as described in the Overview above) of the matching optical host of the ultraviolet variable source.

Host_Color_Class
The color classification of the matching optical host of the ultraviolet variable source, as follows:

    Mdw = color of an M dwarf star;
    RRL = color of an RR Lyrae star;
    QSO = color of a quasar.
  

Host_Redshift
The archival redshift of the matching optical host of the ultraviolet variable source, if available.

Xray_Flag
A flag parameter which is set to 'X' if there is a match for the ultraviolet variable source with an archival X-ray source.

Broad_Type
The GALEX TDS classification of the ultraviolet variable source, as follows:

           Mdw = M dwarf star
          STAR = star;
            CV = cataclysmic variable star;
           RRL = RR Lyrae star;
           BHB = blue horizontal branch star
           LPV = luminous pulsating variable star;
           AGN = active galactic nucleus;
           QSO = quasar;
    Orphan Var = orphan optical host with stochastic UV variability;
  Orphan Trans = orphan optical host with a transient UV source;
  Galaxy Trans = galaxy optical host with a transient UV source;
  Galaxy Flare = galaxy optical host with a flaring UV light curve;
     Point Var = point-source optical host with stochastic UV variability;
   Point Trans = point-source optical host with a transient UV source;
   Point Flare = point-source optical host with a flaring UV light curve;
             ? = none of the above.
  

Class
The HEASARC Browse object classification based on the broad_type parameter value. Note that many of the latter have no exact equivalent class values and have been defaulted to the unidentified class.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 1-May-2013