1WHSP: An IR-based sample of ~1000 VHE γ-ray blazar candidates

Context. Blazars are the dominant type of extragalactic sources at microwave and at γ-ray energies. In the most energetic part of the electromagnetic spectrum (E > 100 GeV) a high fraction of high Galactic latitude sources are blazars of the high synchrotron peaked (HSP) type, that is BL Lac objects with synchrotron power peaking in the UV or in the X-ray band. Building new large samples of HSP blazars is key to understand the properties of jets under extreme conditions, and to study the demographics and the peculiar cosmological evolution of these sources. Aims. High synchrotron peaked blazars are remarkably rare, with only a few hundreds of them expected to be above the sensitivity limits of currently available surveys, some of which include hundreds of millions of sources. To find these very uncommon objects, we have devised a method that combines ALLWISE survey data with multi-frequency selection criteria. Methods. The sample was defined starting from a primary list of infrared colour–colour selected sources from the ALLWISE all sky survey database, and applying further restrictions on IR-radio and IR-X-ray flux ratios. Using a polynomial fit to the multi-frequency data (radio to X-ray), we estimated synchrotron peak frequencies and fluxes of each object. Results. We assembled a sample including 992 sources, which is currently the largest existing list of confirmed and candidates HSP blazars. All objects are expected to radiate up to the highest γ-ray photon energies. In fact, 299 of these are confirmed emitters of GeV γ-ray photons (based on Fermi-LAT catalogues), and 36 have already been detected in the TeV band. The majority of sources in the sample are within reach of the upcoming Cherenkov Telescope Array (CTA), and many may be detectable even by the current generation of Cherenkov telescopes during flaring episodes. The sample includes 425 previously known blazars, 151 new identifications, and 416 HSP candidates (mostly faint sources) for which no optical spectra is available yet. The full 1WHSP catalogue is online at http://www.asdc.asi.it/1whsp/, providing a direct link to the SED building tool where multi-frequency data for each source can be easily visualised.

[1]  Martin G. Cohen,et al.  THE WIDE-FIELD INFRARED SURVEY EXPLORER (WISE): MISSION DESCRIPTION AND INITIAL ON-ORBIT PERFORMANCE , 2010, 1008.0031.

[2]  P. Giommi,et al.  A simplified view of blazars: the very high energy γ-ray vision , 2014, 1410.0497.

[3]  R. D’Abrusco,et al.  INFRARED COLORS OF THE GAMMA-RAY-DETECTED BLAZARS , 2012, 1203.0568.

[4]  Germany,et al.  The classification of BL Lacertae objects: the Ca H&K break , 2002, astro-ph/0207075.

[5]  N. Masetti,et al.  BL LAC CANDIDATES FOR TeV OBSERVATIONS , 2013, 1307.8113.

[6]  Richard L. White,et al.  The FIRST Survey: Faint Images of the Radio Sky at twenty centimeters , 1995 .

[7]  N. Masetti,et al.  BL Lacertae identifications in a ROSAT-selected sample of Fermi unidentified objects , 2013, 1310.1916.

[8]  J. Prochaska,et al.  THE FIRM REDSHIFT LOWER LIMIT OF THE MOST DISTANT TeV-DETECTED BLAZAR PKS 1424+240 , 2013, 1304.4859.

[9]  R. D’Abrusco,et al.  THE WISE GAMMA-RAY STRIP PARAMETERIZATION: THE NATURE OF THE GAMMA-RAY ACTIVE GALACTIC NUCLEI OF UNCERTAIN TYPE , 2012, 1203.1330.

[10]  ESO Very Large Telescope Optical Spectroscopy of BL Lacertae Objects. I. New Redshifts , 2004, astro-ph/0410692.

[11]  P. Giommi,et al.  The discovery of high-power high synchrotron peak blazars , 2012, 1202.2236.

[12]  P. Giommi,et al.  Roma-BZCAT: A multifrequency catalogue of Blazars , 2008, 0810.2206.

[13]  N. Gehrels,et al.  The seven year Swift-XRT point source catalog (1SWXRT) , 2013, 1302.7113.

[14]  Paolo Giommi,et al.  The Connection between X-Ray-- and Radio-selected BL Lacertae Objects , 1995 .

[15]  P. Giommi,et al.  Non-thermal cosmic backgrounds from blazars: the contribution to the CMB, X-ray and γ-ray backgrounds , 2005, astro-ph/0508034.

[16]  U. Schwanke,et al.  Monte carlo design studies for the cherenkov telescope array , 2012, 1210.3503.

[17]  J. Curran,et al.  SUMSS: a wide-field radio imaging survey of the southern sky – II. The source catalogue , 2003, astro-ph/0303188.

[18]  I. M. Stewart,et al.  The XMM-Newton serendipitous survey. V. The Second XMM-Newton serendipitous source catalogue , 2008, 0807.1067.

[19]  P. Giommi,et al.  The Deep X-Ray Radio Blazar Survey. III. Radio Number Counts, Evolutionary Properties, and Luminosity Function of Blazars , 2007, astro-ph/0702740.

[20]  P. Giommi,et al.  A simplified view of blazars: the γ-ray case , 2013, 1302.4331.

[21]  Finland.,et al.  The luminous host galaxies of high redshift BL Lac objects , 2005, astro-ph/0505443.

[22]  P. Giommi,et al.  The sedentary survey of extreme high-energy peaked BL Lacs - III. Results from optical spectroscopy , 2007, 0704.1729.

[23]  P. Giommi,et al.  Multifrequency Catalogue of Blazars (3rd Edition) , 2011 .

[24]  R. Romani,et al.  SPECTROSCOPY OF THE LARGEST EVER γ-RAY-SELECTED BL LAC SAMPLE , 2013, 1301.0323.

[25]  L. Kaper,et al.  Spectroscopy of high-energy BL Lacertae objects with X-shooter on the VLT , 2013, 1311.3809.

[26]  J. Stocke,et al.  HUBBLE/COS OBSERVATIONS OF THE Lyα FOREST TOWARD THE BL Lac OBJECT 1ES 1553+113 , 2010, 1005.2191.

[27]  R. D’Abrusco,et al.  IDENTIFICATION OF THE INFRARED NON-THERMAL EMISSION IN BLAZARS , 2011, 1203.0304.

[28]  E. Greisen,et al.  The NRAO VLA Sky Survey , 1996 .

[29]  T Meures,et al.  Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data , 2014, 1405.5303.

[30]  S. Cenko,et al.  PHOTOMETRICALLY TRIGGERED KECK SPECTROSCOPY OF FERMI BL LACERTAE OBJECTS , 2013, 1308.2756.

[31]  A. Treves.  ESO VLT optical spectroscopy of BL Lac objects , 2009 .

[32]  P. Ciliegi,et al.  The XMM-Newton survey of the ELAIS-S1 field. I. Number counts, angular correlation function and X-ra , 2006 .

[33]  M. V. Fernandes,et al.  Search for TeV Gamma-ray Emission from GRB 100621A, an extremely bright GRB in X-rays, with H.E.S.S , 2014, 1405.0488.

[34]  D. Thompson,et al.  Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars , 2011, 1108.1114.

[35]  J. P. Osborne,et al.  The Swift Serendipitous Survey in deep XRT GRB fields (SwiftFT) ? I. The X-ray catalog and number counts , 2011, 1102.4270.

[36]  M. V. Fernandes,et al.  Measurement of the extragalactic background light imprint on the spectra of the brightest blazars observed with H.E.S.S. , 2012, 1212.3409.

[37]  P. Giommi,et al.  THE SPECTRAL ENERGY DISTRIBUTION OF FERMI BRIGHT BLAZARS , 2009, The Astrophysical Journal.

[38]  Chile,et al.  Near-infrared template spectra of normal galaxies: k-corrections, galaxy models and stellar populations , 2001, astro-ph/0104427.

[39]  P. Giommi,et al.  The sedentary multifrequency survey – I. Statistical identification and cosmological properties of high‐energy peaked BL Lacs , 1999 .

[40]  P. Padovani,et al.  Are both BL Lacs and pulsar wind nebulae the astrophysical counterparts of IceCube neutrino events , 2014, 1406.0376.

[41]  Charles D. Dermer,et al.  TIME DELAY OF CASCADE RADIATION FOR TeV BLAZARS AND THE MEASUREMENT OF THE INTERGALACTIC MAGNETIC FIELD , 2010, 1011.6660.

[42]  R. Falomo,et al.  Imaging Redshifts of BL Lacertae Objects , 2005, astro-ph/0508200.

[43]  P. Giommi,et al.  A simplified view of blazars: clearing the fog around long‐standing selection effects , 2011, 1110.4706.

[44]  B. Skiff,et al.  VizieR Online Data Catalog , 2009 .