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

Abstract

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.

A Novel Study Connecting Ultra-High Energy Cosmic Rays, Neutrinos, and Gamma-Rays

“…Note -For 2FHL (3LAC), the flux F γ (> 50 GeV) (F γ (> 100 MeV)) is in units of 10 −10 ph cm −2 s −1 (10 −8 ph cm −2 s −1 ). The 2WHSP catalog is scanned in "figure of merit" (FoM) as introduced in the text [39].…”

Search for WHSP γ-ray counterparts within Fermi-LAT data: Solving a case of source confusion

“…In general one could consider all photon events with E>100 MeV, but given the fact that HSPs are characterised by hard γ-ray photon spectral index Γ = 1.8 we choose to work at E>300 MeV, avoiding much of the lower energy background. 6 Since the zenith cut is applied, all the observation time where the cut intersects the ROI is excluded. Further cuts are performed with the gtmaktime routine, which generates a list of good time interval (GTIs) to be used for the analysis.…”

“…6 The FOM give an objective way of assessing the likelihood for GeV- of individual sources, specially when selecting targets for observations in the very high energy band (VHE) with Cherenkov Telescope Arrays.…”

“…The 1WHSP catalog, which is the largest sample of HSP objects assembled so far, 6 includes 992 HSP sources, 299 of which have an associated 1/2/3FGL γ-ray counterpart. Nevertheless there is a considerable number of HSPs with relatively bright synchrotron component -11.8< Log(νf ν peak ) <-11.2 which still have no γ-ray counterpart detected.…”

The 2WHSP catalog of VHE blazars

“…Most of the extragalactic VHEdetected objects are HSPs (TeVCat a ); however, the number of known HSPs is still relatively small with only around 1000 cataloged HSPs till now (See Ref. 1,3). In this work, we cross-matched the multi-wavelength data (Infrared, radio, and X-ray), and applied a selection criteria based on the flux density slope between different energy bands: Radio to IR and IR to X-rays.…”