The low-frequency radio catalog of flat spectrum sources

Abstract

A well known property of the gamma-ray sources detected by COS-B in the 1970s, by the Compton Gamma-ray Observatory in the 1990s and recently by the Fermi observations is the presence of radio counterparts, in particular for those associated to extragalactic objects. This observational evidence is the basis of the radio-gamma-ray connection established for the class of active galactic nuclei known as blazars. In particular, the main spectral property of the radio counterparts associated with gamma-ray blazars is that they show a flat spectrum in the GHz frequency range. Our recent analysis dedicated to search blazar-like candidates as potential counterparts for the unidentified gamma-ray sources (UGSs) allowed us to extend the radio-gamma-ray connection in the MHz regime. We also showed that below 1 GHz blazars maintain flat radio spectra. Thus on the basis of these new results, we assembled a low-frequency radio catalog of flat spectrum sources built by combining the radio observations of the Westerbork Northern Sky Survey (WENSS) and of the Westerbork in the southern hemisphere (WISH) catalog with those of the NRAO Very Large Array Sky survey (NVSS). This could be used in the future to search for new, unknown blazar-like counterparts of the gamma-ray sources. First we found NVSS counterparts of WSRT radio sources and then we selected flat spectrum radio sources according to a new spectral criterion specifically defined for radio observations performed below 1 GHz. We also described the main properties of the catalog listing 28358 radio sources and their logN-logS distributions. Finally a comparison with with the Green Bank 6-cm radio source catalog has been performed to investigate the spectral shape of the low-frequency flat spectrum radio sources at higher frequencies.

10 pages, 10 figures, 1 table, ApJS published in 2014 (pre-proof version uploaded)

References in corpus (7)

• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• The VLA Low-frequency Sky Survey
• Roma-BZCAT: A multifrequency catalogue of Blazars
• On the relation between AGN gamma-ray emission and parsec-scale radio jets
• A Unified Catalog of Radio Objects Detected by NVSS, FIRST, WENSS, GB6, and SDSS
• Unveiling the nature of the unidentified gamma-ray sources VI: gamma-ray blazar candidates in the WISH survey and their radio properties
• Swift detection of all previously undetected blazars in a micro-wave flux-limited sample of WMAP foreground sources

Cited by in corpus (18)

• The WISE Blazar-Like Radio-Loud Sources: An All-Sky Catalog Of Candidate Gamma-Ray Blazars
• Optical spectroscopic observations of gamma-ray blazar candidates II. The 2013 KPNO campaign in the Northern Hemisphere
• Optical Spectroscopic Observations of Gamma-ray Blazar Candidates. V. TNG, KPNO, and OAN Observations of Blazar Candidates of Uncertain Type in the Northern Hemisphere
• Optical spectroscopic observations of gamma-ray blazar candidates IV. Results of the 2014 follow-up campaign
• Refining the associations of the Fermi Large Area Telescope Source Catalogs
• Radio Weak BL Lac objects in the Fermi era
• Multi-wavelength variability of CGRaBS J0733+0456: identifying a distant $\gamma$-ray blazar at z = 3.01
• A flat-spectrum flare in S4 0444+63 revealed by a new implementation of multi-wavelength single-dish observations
• New high-frequency radio observations of the Cygnus Loop supernova remnant with the Italian radio telescopes
• Discovery of CO absorption at z=0.05 in G0248+430
• An intergalactic medium temperature from a giant radio galaxy
• A Combined Radio Multi-Survey Catalog of Fermi Unassociated Sources
• A powerful (and likely young) radio-loud quasar at z=5.3
• Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys
• Powerful Radio Sources in the Southern Sky. I. Optical Identifications
• Two new high energy gamma-ray blazar candidates
• Radio spectral properties of cores and extended regions in blazars in the MHz regime
• Exploring the links between quasar winds and radio emission along the Main Sequence at high redshift