Mechanism of very high energy radiation in BL Lacertae object 3C 66A

TL;DR

This paper investigates the high-energy gamma-ray emission mechanisms of blazar 3C 66A by modeling its spectrum observed with Fermi-LAT and VERITAS, highlighting the impact of uncertain redshift on the interpretation.

Contribution

It presents a combined spectral modeling approach for 3C 66A using SSC and EC models, considering different redshift scenarios to explain the observed gamma-ray spectrum.

Findings

The spectrum shows a significant change between 0.2-100 GeV and 200-500 GeV.

The interpretation depends heavily on the assumed redshift value.

Different models (SSC and EC) are suitable under different redshift assumptions.

Abstract

Our goal is to understand the nature of blazars and the mechanisms for the generation of high-energy $\gamma$-rays, through the investigation of the blazar 3C 66A. We model the high energy spectrum of 3C 66A, which has been observed recently with the Fermi-LAT and VERITAS telescope. The spectrum has a hard change from the energy range of 0.2-100 GeV to 200-500 GeV in recent almost contemporaneous observations of two telescopes. The de-absorbed VERITAS spectrum greatly depends on the redshift, which is highly uncertain. If z=0.444 is adopted, we are able to use the SSC model to produce the Fermi-LAT component and the EC model to the VERITAS component. However, if z=0.1, the intrinsic VERITAS spectrum will be softer, there will be a smooth link between the Fermi-LAT and VERITAS spectra which can be explained using a SSC model.