Multi-wavelength emission from 3C 66A: clues on its redshift and gamma-ray emission location

TL;DR

This study models the multi-wavelength emission of blazar 3C 66A to estimate its redshift and gamma-ray emission site, suggesting a redshift around 0.2 and emission occurring outside the broad line region.

Contribution

It introduces a one-zone leptonic jet model to interpret multi-wavelength data and constrains the redshift and emission location of 3C 66A.

Findings

Redshift of 3C 66A likely around 0.2.

Gamma-ray emission region is outside the broad line region.

Theoretical TeV spectra match observations after EBL correction.

Abstract

The quasi-simultaneous multi-wavelength emission of TeV blazar 3C 66A is studied by using a one-zone multi-component leptonic jet model. It is found that the quasi-simultaneous spectral energy distribution (SED) of 3C 66A can be well reproduced, especially its {\it Fermi}-LAT first 3 months average spectrum can be well reproduced by the synchrotron-self Compton (SSC) component plus external Compton (EC) component of the broad line region (BLR). Clues on its redshift and gamma-ray emission location are obtained. The results indicate the following. (i) On the redshift; The theoretical intrinsic TeV spectra can be predicted by extrapolating the reproduced GeV spectra. Through comparing this extrapolated TeV spectra with the extragalactic background light (EBL) corrected observed TeV spectra, it is suggested that the redshift of 3C 66A could be between 0.1 and 0.3, the most likely value is $\sim$ 0.2. (ii) On the gamma-ray emission location; To well reproduce the GeV emission of 3C 66A under different assumptions on BLR, the gamma-ray emission region is always required to be beyond the inner zone of BLR. The BLR absorption effect on gamma-ray emission confirms this point.