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The WISE survey is an all-sky mid-IR survey at 3.4, 4.6, 12, and 22 microns (W1, W2, W3, and W4, respectively) conducted between 2010 January 7 and August 6, during the cryogenic mission phase, and first made available to the public on 2011 April 14. WISE has angular resolutions of 6.1, 6.4, 6.5, and 12.0 arcseconds in its four bands, respectively. The AllWISE data release, which was used for this work, incorporates data from the WISE Full Cryogenic, 3-Band Cryo, and NEOWISE Post-Cryo survey (Mainzer et al. 2014, ApJ, 792, 30) phases, which were co-added to achieve a depth of coverage ~0.4 mag deeper than previous data releases. AllWISE contains the positions, apparent motions, magnitudes, and point-spread function (PSF)-profile fit information for almost 748 million objects. Astrometric calibration of sources in the WISE catalog was done by correlation with bright stars from the 2MASS point source catalog, and the astrometric accuracy for sources in the AllWISE release was further improved by taking into account the proper motions of these reference stars, taken from the fourth USNO CCD Astrograph Catalog (UCAC4, Zacharias et al. 2013, AJ, 145, 44). A comparison with ICRF sources shows that AllWISE Catalog sources in the brightness range of 8 < W1 < 12 mag have positional accuracies to within 50 mas, and half of these sources have positional accuracies to within 20 mas. For more details on the WISE mission, see Wright et al. (2010, AJ, 140, 1868).
The authors took all sources from the AllWISE catalog following Equations (3) and (4) from Mateos et al. (2012, MNRAS, 426, 3271) and they require that all of their sources have S/N >= 5 in the first three bands, as recommended in Mateos et al. (2012); as a further constraint, they limit their results to those with cc_flags = "0000," meaning that the sources are unaffected by known artifacts such as diffraction spikes, persistence, halos, or optical ghosts.
In order to characterize the optical properties of their sample, the authors cross-matched it to SDSS-DR12, which is the final data release of SDSS-III (Eisenstein et al. 2011, AJ, 142, 72), within a radial tolerance of R < 1", obtaining 424,366 matches. To determine the fraction of false positive positional matches (that is, incorrectly correlating an object in their sample with a different SDSS object due to random positional agreement), they performed the same match on a scrambled version of their sample coordinates, determining that less than 1% of other cross-matches are false positive positional matches between the two catalogs. The authors also cross-matched their sample sources with he second release of the Large Quasar Astrometric Catalog (LQAC-2; Souchay et al. 2012, A&A, 537, A99), which contains 187,504 quasars, including radio-selected quasars from the ICRF2, optically selected quasars from SDSS, and infrared-selected quasars from 2MASS, and thus represents a robust sample of quasars over a wide range of wavelengths. They find that 93,403 quasars from LQAC-2 have clean detections. The majority of non-detections are due to sources in LQAC-2 that are too faint, having R >~ 19.
NWAY extends previous distance- and sky density-based association methods and, using one or more priors (e.g. colors, magnitudes), weights the probability that sources from two or more catalogs are simultaneously associated on the basis of their observable characteristics. Here, counterparts have been determined using a Wide-field Infrared Survey Explorer (WISE) color-magnitude prior. A reference sample of 4,524 XMM/Chandra and Swift X-ray sources demonstrates a reliability of 94.7 per cent for 2RXS sources. Combining the results of this work and of the matching of XMM-Newton Slew Survey, Version 2 (XMMSL2) sources also reported in this study (the results of the latter are available as the HEASARC's database table NWAYAWGXMM) with Chandra-COSMOS data, the authors propose a new separation between stars and AGN in the X-ray/WISE flux-magnitude plane, that is valid over six orders of magnitude. The authors also release the NWAY code and its user manual. NWAY was extensively tested with XMM-COSMOS data.
Using two different sets of priors, the authors find an agreement of 96 per cent and 99 per cent with published Likelihood Ratio methods. Their results were achieved faster and without any follow-up visual inspection. With the advent of deep and wide area surveys in X-rays (e.g. SRG/eROSITA, Athena/WFI) and radio (ASKAP/EMU, LOFAR, APERTIF, etc.), NWAY will provide a powerful and reliable counterpart identification tool.
For all the available options, see the NWAY manual at https://github.com/JohannesBuchner/nway/raw/master/doc/nway-manual.pdf.
NWAY extends previous distance- and sky density-based association methods and, using one or more priors (e.g. colors, magnitudes), weights the probability that sources from two or more catalogs are simultaneously associated on the basis of their observable characteristics. Here, counterparts have been determined using a Wide-field Infrared Survey Explorer (WISE) color-magnitude prior. A reference sample of 4,524 XMM/Chandra and Swift X-ray sources demonstrates a reliability of 97.4 per cent for XMMSL2 sources. Combining the results of this work and of the matching of ROSAT All-Sky Survey 2RXS sources also reported in this study (the results of the latter are available as the HEASARC's database table NWAYAWGROS) with Chandra-COSMOS data, the authors propose a new separation between stars and AGN in the X-ray/WISE flux-magnitude plane, that is valid over six orders of magnitude. The authors also release the NWAY code and its user manual. NWAY was extensively tested with XMM-COSMOS data.
Using two different sets of priors, the authors find an agreement of 96 per cent and 99 per cent with published Likelihood Ratio methods. Their results were achieved faster and without any follow-up visual inspection. With the advent of deep and wide area surveys in X-rays (e.g. SRG/eROSITA, Athena/WFI) and radio (ASKAP/EMU, LOFAR, APERTIF, etc.), NWAY will provide a powerful and reliable counterpart identification tool.
For all the available options, see the NWAY manual at https://github.com/JohannesBuchner/nway/raw/master/doc/nway-manual.pdf.
The authors have performed an all-sky survey for z ~ 1, FUV-bright quasars selected from GALEX and WISE photometry. In several of the observing runs, conditions were unexpectedly favorable and we exhausted the primary candidates at certain right ascension ranges. To fill the remaining observing time, they generated a secondary candidate list. This secondary set of 2,010 candidates is also contained in this HEASARC table (entries with source_sample = 'S').
The authors proceeded to obtain discovery-quality long-slit spectra (i.e., low-dispersion, large-wavelength coverage, modest signal-to-noise ratio (S/N) of their UV-bright Quasar Survey (UVQS) candidates in one calendar year. The principal facilities were: (i) the dual Kast spectrometer on the 3m Shane telescope at the Lick Observatory; (ii) the Boller & Chivens (BCS) spectrometer on the Irenee du Pont 100-inch telescope at the Las Campanas Observatory; and (iii) the Calar Alto Faint Object Spectrograph on the CAHA 2.2-meter telescope at the Calar Alto Observatory (CAHA). They acquired an additional ~20 spectra on larger aperture telescopes (Keck/ESI, MMT/MBC, Magellan/MagE) during twilight or under poor observing conditions. Typical exposure times were limited to < ~200s, with adjustments for fainter sources or sub-optimal observing conditions. Table 3 in the reference paper provides a list of the details of the observations of these candidates. From the total candidates list of 3,460 objects, the authors measured high-quality redshifts (redshift quality flag values of 3 or greater) for 1,121 sources. They assumed that every source with a recessional velocity vr = z * c < 500 km s-1 was "Galactic", which they associate with the Galaxy and members of the Local Group. This included sources where the eigenspectra fits were poor yet a low vr was indisputable (e.g., stars). Many of these were assigned z = 0 exactly. The remainder of the UVQS sources were assumed to be extragalactic AGN, and the derived redshift information for these sources (which was given in Table 4 of the reference paper) has been incorporated into this HEASARC representation of UVQS. Finally, there were 93 sources with good-quality spectra for which we cannot the authors could not recover a secure redshift. The majority of these have been previously cataloged as blazars (or BL Lac objects). Table 6 in the reference paper lists the sample of these unknown or insecure redshift objects.
The WISE magnitudes in the [3.4], [4.6], [12] and [22] um nominal filters are in the Vega system. The values of three WISE magnitudes, namely [3.4], [4.6], and [12], and of the colors derived using those magnitudes, have been corrected for galactic extinction according to the extinction law presented by Draine (2003, ARA&A, 41, 241). In their study, the authors adopt the nomenclature proposed in the Multi-wavelength Blazar Catalog (BZCat) that labels BL Lac objects as 'BZBs' and flat-spectrum radio quasars (FSRQs) as 'BZQs'.
The authors have assembled the largest and most complete catalog of HSP blazars to date, which includes 1691 sources. A number of population properties, such as infrared colors, synchrotron peak, redshift distributions, and gamma-ray spectral properties, have been used to characterize the sample and maximize completeness. The authors also derived the radio log N - log S distribution. This catalog has already been used to provide seeds to discover new very high energy objects within Fermi-LAT data and to look for the counterparts of neutrino and ultra-high energy cosmic ray sources, showing its potential for the identification of promising high-energy gamma-ray sources and multi-messenger targets.
This table comprises the 2WHSP catalog, a multi-frequency catalog of HSP. It contains 1691 sources, 288 of which are newly identified HSPs, 540 are previously known HSPs, 814 are HSP candidates, 45 are HSP blazars taken from the 2FHL catalog, and 4 from TeVCat (http://tevcat.uchicago.edu).