Research Note

On the redshift of the blazar PKS 0447-439^⋆,⋆⋆

¹ Department of Astronomy and AstrophysicsUniversity of California, 1156 High Street, Santa Cruz, CA 95064, USA
e-mail: mfumagalli@ucolick.org
² Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
³ Department of Chemistry and Physics, Saint Michael’s College, One Winooski Park, Colchester, VT 05439, USA
⁴ UCO/Lick Observatory, University of California, 1156 High Street, Santa Cruz, CA 95064, USA
⁵ Università dell’Insubria, via Valleggio 11, 22100 Como, Italy
⁶ INFN Milano-Bicocca, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy

Received: 16 July 2012
Accepted: 8 August 2012

Abstract

PKS 0447-439 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 γ-rays cannot freely propagate in the z ≳ 1 universe. In this research note, we present a new MagE/Magellan spectrum of PKS 0447-439 with exquisite signal-to-noise (S/N > 150 at 6500 Å). Our analysis confirms the presence of the previously-reported absorption line at 6280 Å, 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.