Optical spectroscopy of the gamma-ray bright blazars PKS 0447-439 and PMN J0630-24

TL;DR

This study provides high-quality optical spectra of two gamma-ray bright blazars, revealing absorption lines that establish their high redshifts, aiding in understanding their nature and the extragalactic background light.

Contribution

It presents the first high-resolution optical spectroscopy of these blazars, determining their redshifts despite their featureless spectra.

Findings

PKS 0447-439 at z>=1.246

PMN J0630-24 at z>=1.238

Spectroscopy reveals absorption lines in BL Lacs

Abstract

The large majority of sources detected by the Fermi Gamma-ray Space Telescope are blazars, belonging in particular to the blazar subclass of BL Lacertae objects (BL Lacs). BL Lacs often have featureless optical spectra, which make it difficult and sometimes impossible to determine their redshifts. This presents a severe impediment for the use of BL Lacs to measure the spectrum of the extragalactic background light through its interaction with high-energy gamma-ray photons. I present here high-quality optical spectroscopy of two of the brightest gamma-ray blazars, namely, PKS 0447-439 and PMN J0630-24. The medium-resolution and high signal-to-noise ratio optical spectra show clear absorption lines, which place these BL Lacs at relatively high redshifts of z>=1.246 for PKS 0447-439 and z>=1.238 for PMN J0630-24.