A model-driven search for extreme BL Lacs among LAT BCU

TL;DR

This paper identifies potential extreme BL Lac objects among gamma-ray sources by cross-matching catalogs, analyzing multi-wavelength data, modeling their spectra, and proposing a new selection method for VHE observations.

Contribution

It introduces a model-driven approach to select extreme BL Lac candidates for VHE detection, combining catalog cross-matching, spectral analysis, and a novel target selection method.

Findings

Identified 23 high-synchrotron-peaked blazar candidates with multi-wavelength coverage.

Performed detailed spectral modeling including extragalactic background light attenuation.

Proposed a new method for selecting extreme BL Lacs for ground-based VHE telescopes.

Abstract

The emission of very-high-energy photons (VHE, E$>$100 GeV) in active galactic nuclei (AGN) is closely connected with the production of ultra-relativistic particles. Among AGN, the subclass of extreme BL Lacertae are of particular interest because they challenge state-of-art models on how these cosmic particle accelerators operate. By cross-matching two gamma-ray catalogs (this is, 4FGL-DR2 and 2BIGB), we identified 23 high-synchrotron-peaked (HSP) blazar candidates with photometric or spectroscopic redshifts, good multi-wavelength coverage, that are possibly detectable by VHE instruments. We performed a new analysis of Fermi Large Area Telescope data including the effects of attenuation from the extragalactic background light and complemented these results by collecting multiwavelength data from optical, radio and X-ray archival observations. Their broadband spectral energy distributions were interpreted in terms of synchrotron-self-Compton models with external-Compton components and compared with the properties of prototypical extreme HSP blazars. Finally, we test their detectability with imaging atmospheric Cherenkov telescopes (IACTs) and propose a new method for selecting these extreme targets for these ground-based telescopes.