2WHSP: A multi-frequency selected catalogue of high energy and very high energy γ-ray blazars and blazar candidates^⋆

¹ Sapienza Università di Roma, ICRANetDipartimento di Fisica, Piazzale Aldo Moro 5, 00185 Roma, Italy
e-mail: stsun1223@hotmail.com
² Italian Space Agency, ASI, via del Politecnico snc, 00133 Roma, Italy
³ ICRANet, P.zza della Repubblica 10, 65122 Pescara, Italy
⁴ ICRANet-Rio, CBPF, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, Brazil
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
⁶ Associated to INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
e-mail: yuling.chang@asdc.asi.it

Received: 5 August 2016
Accepted: 18 September 2016

Abstract

Aims. High synchrotron peaked blazars (HSPs) dominate the γ-ray sky at energies higher than a few GeV; however, only a few hundred blazars of this type have been cataloged so far. In this paper we present the 2WHSP sample, the largest and most complete list of HSP blazars available to date, which is an expansion of the 1WHSP catalogue of γ-ray source candidates off the Galactic plane.

Methods. We cross-matched a number of multi-wavelength surveys (in the radio, infrared and X-ray bands) and applied selection criteria based on the radio to IR and IR to X-ray spectral slopes. To ensure the selection of genuine HSPs, we examined the SED of each candidate and estimated the peak frequency of its synchrotron emission (ν_peak) using the ASDC SED tool, including only sources with ν_peak > 10¹⁵ Hz (equivalent to ν_peak > 4 eV).

Results. We have assembled the largest and most complete catalogue of HSP blazars to date, which includes 1691 sources. A number of population properties, such as infrared colours, synchrotron peak, redshift distributions, and γ-ray spectral properties have been used to characterise the sample and maximize completeness. We also derived the radio log N–log S distribution. This catalogue 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 γ-ray  sources and multi-messenger targets.