VERITAS Observations of Six Bright, Hard-Spectrum Fermi-LAT Blazars

TL;DR

This study observed six bright, hard-spectrum Fermi-LAT blazars with VERITAS but detected no VHE gamma-ray emission, providing upper limits and modeling their spectral energy distributions to understand their emission mechanisms.

Contribution

First-time VHE observations of selected bright blazars with detailed SED modeling, setting constraints on their gamma-ray emission and physical properties.

Findings

No VHE emission detected from the six blazars.

Spectral energy distributions suggest intermediate- to high-synchrotron-peak blazar classification.

Most sources have particle-dominated emission regions.

Abstract

We report on VERITAS very-high-energy (VHE; E>100 GeV) observations of six blazars selected from the Fermi Large Area Telescope First Source Catalog (1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE band, taking gamma-ray absorption by the extragalactic background light into account. This allowed the selection of six bright, hard-spectrum blazars that were good candidate TeV emitters. Spectroscopic redshift measurements were attempted with the Keck Telescope for the targets without Sloan Digital Sky Survey (SDSS) spectroscopic data. No VHE emission is detected during the observations of the six sources described here. Corresponding TeV upper limits are presented, along with contemporaneous Fermi observations and non-concurrent Swift UVOT and XRT data. The blazar broadband spectral energy distributions (SEDs) are assembled and modeled with a single-zone synchrotron self-Compton model. The SED built for each of the six blazars show a synchrotron peak bordering between the intermediate- and high-spectrum-peak classifications, with four of the six resulting in particle-dominated emission regions.