Michele Fumagalli, Amy Furniss, John M. O'Meara, J. Xavier Prochaska, David A. Williams, Emanuele P. Farina
PKS0447-43 is one of the brightest hard-spectrum blazars from which very high energy emission has been detected. Recently, Landt (2012) reported a lower limit of z>1.246 for the redshift of this BL Lacertae object, challenging the current paradigm in which gamma-rays cannot freely propagate in the z>1 universe. In this research note, we present a new MagE/Magellan spectrum of PKS0447-43 with exquisite signal-to-noise (S/N>150 a 6500 A). Our analysis confirms the presence of the previously-reported absorption line at 6280 A which, however, we identify 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.
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http://arxiv.org/abs/1207.3592
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