XMM-Newton observations of 3C 273

Abstract

A series of nine XMM-Newton observations of the radio-loud quasar 3C 273 are presented, concentrating mainly on the soft excess. Although most of the individual observations do not show evidence for iron emission, co-adding them reveals a weak, broad line (EW ~56 eV). The soft excess component is found to vary, confirming previous work, and can be well fitted with multiple blackbody components, with temperatures ranging between ~40 and ~330 eV, together with a power law. Alternatively, a Comptonization model also provides a good fit, with a mean electron temperature of ~350 eV, although this value is higher when the soft excess is more luminous over the 0.5-10 keV energy band. In the reflection grating spectrometer spectrum of 3C 273, a strong detection of the O VII Heα absorption line at zero redshift is made; this may originate in warm gas in the local intergalactic medium, consistent with the findings of both Fang, Sembach & Canizares and Rasmussen, Kahn & Paerels.