TeV-peaked candidate BL Lac objects

TL;DR

This paper introduces a new selection criterion for identifying TeV-peaked BL Lac objects, which are extreme and rare sources crucial for astrophysical studies, by combining X-ray, gamma-ray, and infrared data.

Contribution

A novel, simple method to select TeV-peaked BL Lac candidates using flux ratios, independent of radio flux, enhancing the identification of these rare sources.

Findings

Produced a list of 47 candidate TeV-peaked BL Lacs.

The method effectively identifies faint radio sources.

Facilitates future TeV observations and studies.

Abstract

BL Lac objects can be extreme in two ways: with their synchrotron emission, peaking beyond 1 keV in their spectral energy distribution, or with their gamma-ray emission, peaking at multi-TeV energies up to and beyond 10-20 TeV, like 1ES 0229+200. This second type of extreme BL Lacs --which we can name "TeV-peaked BL Lacs" is not well explained by the usual synchrotron self-Compton scenarios for BL Lacs. These sources are also important as probes for the intergalactic diffuse infrared background and cosmic magnetic fields, as well as possible sites of production of ultra-high-energy cosmic rays and neutrinos. However, all these studies are hindered by their still very limited number. Here I propose a new, simple criterium to select the best candidates for TeV observations, specifically aimed at this peculiar type of BL Lac objects by combining X-ray, gamma-ray and infrared data. It is based on the observation of a clustering towards a high X-ray to GeV gamma-ray flux ratio, and it does not rely on the radio flux or X-ray spectrum. This makes it suitable to find TeV-peaked sources also with very faint radio emission. Taking advantage of the Fermi all-sky gamma-ray survey applied to the ROMA-BZCAT and Sedentary Survey samples, I produce an initial list of 47 TeV-peaked candidates for observations with present and future air-Cherenkov telescopes.