On the redshift of the blazar PKS0447-439

Abstract

PKS0447-439 is one of the BL Lacertae objects that have been detected at very high energy. There has been a recent report of a lower limit of z>1.246 for the redshift of this blazar, challenging the current paradigm in which very high-energy gamma-rays cannot freely propagate in the z>1 universe. In this research note, we present a new MagE/Magellan spectrum of PKS0447-439 with exquisite signal-to-noise (S/N>150 at 6500A). Our analysis confirms the presence of the previously-reported absorption line at 6280A, which we identify, however, with a known telluric absorption, invalidating the claim that this blazar lies at z>1. Since no other extragalactic spectral features are detected, we cannot establish a redshift based on our spectrum.

3 pages, 2 figures. Research note. A&A accepted

References in corpus (2)

• ESO-VLT optical spectroscopy of BL Lac objects: II. New redshifts, featureless objects and classification assessments
• On the relationship between BL Lacertae objects and radio galaxies

Cited by in corpus (1)

• The BL-Lac gamma-ray blazar PKS 0447-439 as a probable member of a group of galaxies at z=0.343