Bulk Compton motion in the luminous quasar 4C04.42?

Abstract

We present the broadband analysis of the powerful quasar 4C04.42 (z = 0.965) observed by XMM-Newton and INTEGRAL. The 0.2-200keV spectrum is well reproduced with a hard power-law component (Γ ~ 1.2), augmented by a soft component below 2keV (observer frame), which is described by a thermal blackbody with temperature kT ⋍ 0.15keV. Alternatively, a broken power law with E_break = 2keV and ΔΓ = 0.4 can equally well describe the data. Using archival data we compile the not-simultaneous spectral energy distribution (SED) of the source from radio to gamma-ray frequencies. The SED shows two main components: the low frequency one produced by Synchrotron radiation from the electrons moving in the jet and the high-energy one produced through external Compton scattering of the electrons with the photon field of the broad line region. Within this scenario the excess emission in the soft X-ray band can be interpreted as due to bulk Compton radiation of cold electrons. However, some other processes, briefly discussed in the text, can also reproduce the observed bump.