The HST ultraviolet spectrum of the nucleus of NGC 1275: Fermi-accelerated Lyalpha emission

Abstract

We present an HST FOS spectrum of the nucleus of NGC 1275. The narrow part of the Lyalpha line is double-peaked, with one emission line centred at the systemic velocity of the 5000 km s^-1 system and the other blueshifted by ~450 km s^-1. We show that the short-wavelength component is probably formed by Fermi acceleration across a shock front. The conditions required for this process occur in the inner parts of cooling flows.