Emission models and EBL as a tool to measure the redshift of BL Lac objects

TL;DR

This paper presents a novel method for estimating the redshift of BL Lac objects by fitting multi-wavelength spectral energy distributions with SSC models and comparing observed VHE gamma-ray fluxes with EBL-absorbed predictions.

Contribution

The method combines multi-wavelength observations and SSC modeling to determine redshift, providing a new approach for sources with unknown distances.

Findings

Successfully applied the method to specific BL Lac objects

Derived redshift estimates consistent with other measurements

Demonstrated the effectiveness of EBL absorption modeling

Abstract

We introduce a new method to determine the redshift of unknown-redshift BL Lac Objects. The method relies on simultaneous multi-wavelength (MWL) observations of BL Lac objects in optical, X-ray, HE (E>100 MeV) gamma-rays and VHE (E>100 GeV)gamma-rays. It involves best-fitting spectral energy distribution (SED) from optical through HE gamma-rays with a Synchrotron-Self-Compton (SSC) model. We extrapolate such best fitting model into VHE regime, and assume that it represents the intrinsic emission of the object. We then compare the observed VHE flux which has been affected by the interaction with Extragalactic Background Light (EBL). Constraining the measured vs intrinsic emission leads to the determination of gamma-gamma opacity. Comparing the obtained opacity with the predicted opacity based on EBL model, we obtain the redshift of the photon source.