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SWSDSSQSO - Swift Simultaneous UV, Optical, and X-Ray Observed Quasar Catalog

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Overview

The authors have compiled a catalog of optically selected quasars with simultaneous observations in UV/optical and X-ray bands by the Swift Gamma-ray Burst Explorer. Objects in this catalog are identified by matching the Swift pointings with the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasar catalog. The final catalog contains 843 objects, among which 637 have both Ultraviolet Optical Telescope (UVOT) and X-Ray Telescope (XRT) observations and 354 of which are detected by both instruments. The overall X-ray detection rate is ~ 60% which rises to ~ 85% among sources with at least 10 ks of XRT exposure time. The authors construct the time-averaged spectral energy distribution (SED) for each of the 354 quasars using UVOT photometric measurements and XRT spectra. From model fits to these SEDs, they find that the big blue bump contributes about ~ 0.3 dex to the quasar luminosity. The authors re-visit the alphaox - L2500A relation by selecting a clean sample with only Type 1 radio-quiet quasars; the dispersion of this relation is reduced by at least 15% compared with studies that use non-simultaneous UV/optical and X-ray data. They find only a weak correlation between Lbol/LEdd and alphaUV. They do not find significant correlations between alphax and alphaox, alphaox and alphaUV, and alphax and log L(0.3-10 keV). The correlations between alphaUV and alphax, alphaox and alphax, alphaox and alphaUV, Lbol/LEdd and alphax, and Lbol/LEdd and alphaox are stronger among low-redshift quasars, indicating that these correlations are likely driven by the changes of SED shape with accretion state.

This quasar sample was compiled in the following steps:

1. Candidate objects for the catalog were selected as any SDSS DR5 quasar that lie within 20 arcminutes of the center of the Swift FOV in any pointing from launch through 2008 June.

2. XRT data were processed to obtain X-ray count rates, spectra, and spectral parameters.

3. UVOT data were processed to obtain UV and optical photometry.

4. UVOT photometry were supplemented with measurements at other wavelengths from published catalogs.

5. Quasar SEDs were constructed.

6. Additional parameters were calculated based on the SEDs of each quasar. The raw sample is constructed by matching 3.5 years Swift pointings and the SDSS DR5 quasar catalog and contains 1034 objects.

This HEASARC version of this catalog contains all 1034 objects in the "raw" catalog. To select only the 843 objects in the "final" catalog, the user should specify catalog_flag = 1 in any searches of this table.


Catalog Bibcode

2012ApJS..201...10W

References

A Quasar Catalog with Simultaneous UV, Optical, and X-Ray Observations by Swift
    Wu J., Vanden Berk D., Grupe D., Koch S., Gelbord J., Schneider D. P.,
    Gronwall C., Wesolowski S., Porterfield, B. L.
   <Astrophys. J. Suppl. 201, 10. (2012).>
   =2012ApJS..201...10W

Provenance

This table was created by the HEASARC in August 2012 based on an electronic version of Table 8 from the reference paper which was obtained from the ApJS web site.

Parameters

Name
The SDSS DR5 designation of the quasar in the standard J2000.0 position based notation, e.g., 'SDSS JHHMMSS.ss+DDMMSS.s'.

RA
The Right Ascension of the SDSS quasar in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

Dec
The Declination of the SDSS quasar in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 10-6 degrees in the original table.

LII
The Galactic Longitude of the SDSS quasar.

BII
The Galactic Latitude of the SDSS quasar.

Redshift
The redshift of the quasar as given in the SDSS DR5 Quasar Catalog.

Abs_Imag
The absolute magnitude of the quasar in the i band from the SDSS DR5 Quasar Catalog.

Umag
The BEST PSF u-band magnitude of the quasar (not corrected for Galactic extinction).

Quality_Flag
This flag parameter indicates the quality of the available Swift data for the quasar. The authors classify objects in the database into four types based on data availability (see Table 4 of the reference paper). In their terminology, "useful data" includes both detections and non-detections. Type 'a' contains 637 objects that have useful data from both the UVOT and the XRT. Among them, 345 are detected by UVOT and XRT. Type 'b' contains the 38 objects that have useful data from UVOT but not XRT. These objects cannot be included in correlation analysis. Type 'c' contains 168 objects that have only useful data from XRT but not UVOT. The authors only create the XRT energy spectra for these objects. Type 'd' contains 191 objects that are bereft of any useful data from UVOT or XRT. These objects are included in this HEASARC table with a quality_flag value of 0. All 843 other objects are considered to comprise the "final" catalog and have been given quality_flag values of 1.

Catalog_Flag
This Boolean flag parameter is set to 1 to indicate that an entry is included in the "final" SDSS/Swift quasar catalog.

SED_Flag
This Boolean flag parameter is set to 1 to indicate that a quasar SED was constructed.

Num_2MASS_Datapts
The number of 2MASS photometric data points for the quasar.

Num_Swift_Datapts
The number of Swift/UVOT photometric data points for the quasar.

XRT_Quality_Flag
This flag parameter indicates the quality of the Swift/XRT data for the quasar, as follows:

     o = Source outside XRT FOV (229 objects);
     w = weak X-ray source, i.e., fewer than 10 background-subtracted X-ray
         photons (406 objects);
     a = acceptable X-ray source, i.e., between 10 and 100 background-subtracted
         X-ray photons (296 objects);
     g = good X-ray source, i.e., more than 100 background-subtracted X-ray
         photons (103 objects).
  

Quasar_Type
The classification of the quasar. See Section 5.1 of the reference paper for more details.

XRT_Model
This flag parameter indicates the model used to fit the XRT spectrum of the quasar, 'a', 'b', 'c' or 'd'. For each object with more than ~ 10 background-subtracted X-ray counts, the authors fit the X-ray spectrum with an absorbed powerlaw model. This model includes Galactic column density along the line of sight to the quasar NH,G and possibly additional absorption intrinsic to it NH,i. The values of NH,G are fixed based upon the Leiden/Argentine/Bonn survey of Galactic H I (Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen; Kalberla et al. 2005, A&A, 440, 775). The authors define four variations of this model, depending upon whether the photon spectral index (alphax) or NH,i are allowed to vary as a fixed parameter. These four variations depend upon whether the spectral index alphax and/or NH,i are allowed to vary, or are fixed. (See Table 2 of the reference paper for more details).

Red_Flag
This flag parameter is set to 1 to indicates that the color of the quasar is "red". A simple analysis of the quasar SED may not apply to strong X-ray absorption quasars. An example is shown in the first SED plot in Figure 10 of the refernce paper. In this case, the absorption leads to a flat UV slope in addition to low X-ray emission in the soft X-ray band. In these cases, the EXP model does not produce a "bump" but a "dip" in the EUV region and the corresponding integrated bolometric luminosity is not reliable. These quasars (83 objects) are flagged as "red" and were not included in the authors' "clean" sample discussed in Section 5.1 of the reference paper. The HEASARC notes that there are 10 objects with red_flag values of -1: the meaning of this value is not known to the HEASARC.

SDSS_Fit_Flag
This Boolean flag parameter is set to 1 to indicate that the SDSS spectrum of the quasar is fit, else to 0 if it is not fit.

XRT_Photon_Index
The X-ray photon index of the quasar between 0.3 and 10 keV as determined from the Swift/XRT spectrum.

XRT_Photon_Index_Neg_Err
The 1-sigma lower error in the Swift/XRT photon index. A value of 0.000 for this error means that the parameter value was fixed.

XRT_Photon_Index_Pos_Err
The 1-sigma upper error in the Swift/XRT photon index. A value of 0.000 for this error means that the parameter value was fixed.

XRT_Hardness_Ratio
The X-ray hardness ratio HR of the Swift/XRT spectrum of the quasar, defined as HR = (H-S)/(H+S), where H is the number of counts between 1 and 10 keV, and S is the number of counts between 0.3 and 1 keV.

Log_Fx_Obs
The logarithm of the observed 0.3-10 keV Swift/XRT flux of the quasar, in erg s-1 cm-2.

Log_Fx
The logarithm of the unabsorbed 0.3-10 keV Swift/XRT flux of the quasar, in erg s-1 cm-2.

Log_L_2keV
The logarithm of the 2-keV monochromatic luminosity of the quasar, in erg s-1 Hz-1.

Log_L_2keV_Error
The 1-sigma uncertainty in the logarithm of the 2-keV monochromatic luminosity of the quasar, in erg s-1 Hz-1.

Log_Lx
The integrated 0.3-10 keV luminosity of the quasar, in erg s-1.

XRT_Detection_Flag
This flag parameter indicates the status of the Swift/XRT detection for the quasar:

       -1 = not observed,
        0 = not detected,
        1 = detected.
  

XRT_Count_Rate
The Swift/XRT source count rate of the quasar, in cts s-1.

XRT_Exposure
The total Swift/XRT exposure time on the quasar, in seconds.

NH_Gal
The Galactic column density towards the quasar, NH,G, in H atoms cm-2. The values of NH,G are fixed based upon the Leiden/Argentine/Bonn survey of Galactic H I (Hartmann & Burton 1997, Atlas of Galactic Neutral Hydrogen; Kalberla et al. 2005, A&A, 440, 775).

NH_Int
The intrinsic column density, NH,i, in H atoms cm-2, as determined from the fit to the Swift/XRT spectrum (for xrt_model values of 'c' and 'd'), or as fixed at 0.0 (for xrt_model values of 'a' and 'b').

NH_Int_Neg_Err
The 1-sigma lower error in the intrinsic column density, in H atoms cm-2, as determined from the fit to the Swift/XRT spectrum (for xrt_model values of 'c' and 'd'), or as fixed at 0.0 (for xrt_model values of 'a' and 'b').

NH_Int_Pos_Err
The 1-sigma upper error in the intrinsic Column density, in H atoms cm-2, as determined from the fit to the Swift/XRT spectrum (for xrt_model values of 'c' and 'd'), or as fixed at 0.0 (for xrt_model values of 'a' and 'b').

Vmag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

Vmag_Exposure
The total Swift/UVOT V-band exposure time for the quasar, in seconds.

Log_Vmag_Flux_Dens
The logarithm of the flux density in the Swift/UVOT V-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_Vmag_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT V-band for the quasar, in erg s-1 cm-2 Angstrom-1,

Bmag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

Bmag_Exposure
The total Swift/UVOT B-band exposure time for the quasar, in seconds.

Log_Bmag_Flux_Dens
The logarithm of the flux density in the Swift/UVOT B-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_Bmag_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT B-band for the quasar, in erg s-1 cm-2 Angstrom-1.

Umag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

Umag_Exposure
The total Swift/UVOT U-band exposure time for the quasar, in seconds.

Log_Umag_Flux_Dens
The logarithm of the flux density in the Swift/UVOT U-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_Umag_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT U-band for the quasar, in erg s-1 cm-2 Angstrom-1.

UVW1_Mag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

UVW1_Mag_Exposure
The total Swift/UVOT UVW1-band exposure time for the quasar, in seconds.

Log_UVW1_Flux_Dens
The logarithm of the flux density in the Swift/UVOT UVW1-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_UVW1_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT UVW1-band for the quasar, in erg s-1 cm-2 Angstrom-1.

UVM2_Mag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

UVM2_Mag_Exposure
The total Swift/UVOT UVM2-band exposure time for the quasar, in seconds.

Log_UVM2_Flux_Dens
The logarithm of the flux density in the Swift/UVOT UVM2-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_UVM2_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT UVM2-band for the quasar, in erg s-1 cm-2 Angstrom-1.

UVW2_Mag_Flag
This flag parameter is set to 1 if there is available photometry in the corresponding Swift/UVOT band for the quasar, else is set to 0, i.e., if there is none.

UVW2_Mag_Exposure
The total Swift/UVOT UVW2-band exposure time for the quasar, in seconds.

Log_UVW2_Flux_Dens
The logarithm of the flux density in the Swift/UVOT UVW2-band for the quasar, in erg s-1 cm-2 Angstrom-1, and corrected for Galactic reddening.

Log_UVW2_Flux_Dens_Error
The 1-sigma uncertainty in the logarithm of the flux density in the Swift/UVOT UVW2-band for the quasar, in erg s-1 cm-2 Angstrom-1.

UV_Spectral_Index
The UV spectral index of the quasar, alphaUV,ph found from fitting the UV photometric data.

UV_Spectral_Index_Error
The 1-sigma uncertainty in the UV spectral index of the quasar, alphaUV,ph found from fitting the UV photometric data.

Log_L_2500a
The logarithm of the 2500-Angstrom monochromatic luminosity of the quasar, found from fitting the UV photometric data, in erg s-1 Hz-1.

Log_L_2500a_Error
The 1-sigma uncertainty in the logarithm of the 2500-Angstrom monochromatic luminosity of the quasar, found from fitting the UV photometric data, in erg s-1 Hz-1.

Alpha_Ox
The optical/UV to X-ray spectral index, alphaox, for the quasar found using the monochromatic luminosities at 2500 Angstroms and 2 keV, log_l_2500a and log_l_2kev, respectively, and the relation alphaox = 0.3838 * (log_l_2kev - log_l_2500a), as given in Equation (1) of the reference paper.

Alpha_Ox_Error
The 1-sigma uncertainty in the optical/UV to X-ray spectral index, alphaox.

Log_Black_Hole_Mass
The logarithm of the black hole mass for the quasar, in solar masses, calculated using the emission line FWHM and the corresponding continuum flux as obtained from power-law fitting of the photometric data points as discussed in Section 3.7 of the reference paper.

Log_Lbol_Exp
The logarithm of the bolometric luminosity of the quasar, in erg s-1, found by integrating for best-fit exponential decay (EXP) model to its SED (see Section 3.6 of the reference paper for more details).

Log_Lbol_Tpl
The logarithm of the bolometric luminosity of the quasar, in erg s-1, found by integrating for best-fit triple power law (TPL) model to its SED (see Section 3.6 of the reference paper for more details).

Class
The HEASARC Browse object classification of the quasar, based on the value of the quasar_type parameter.


Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 3-Aug-2012