Multiwavelength observations of the powerful gamma-ray quasar PKS 1510-089: Clues on the jet composition

We present the results from a multiwavelength campaign conducted in 2006 August of the powerful γ-ray quasar PKS 1510-089 (z = 0.361). This campaign commenced with a deep Suzaku observation lasting 3 days for a total exposure time of 120 ks and continued with Swift monitoring over 18 days. Besides Swift observations, the campaign included ground-based optical and radio data and yielded a quasi-simultaneous broadband spectrum from 10⁹ to 10¹⁹ Hz. The Suzaku observation provided a high signal-to-noise ratio X-ray spectrum, which is well represented by an extremely hard power law with a photon index of Γ ∼ 1.2, augmented by a soft component apparent below 1 keV, which is well described by a blackbody model with a temperature of kT ≃ 0.2 keV. Monitoring by Suzaku revealed temporal variability that differs between the low- and high-energy bands, again suggesting the presence of a second, variable component in addition to the primary power-law emission. We model the broadband spectrum, assuming that the high-energy spectral component results from Comptonization of infrared radiation produced by hot dust located in the surrounding molecular torus. The adopted internal shock scenario implies that the power of the jet is dominated by protons, but with a number of electrons and/or positrons that exceeds the number of protons by a factor of ∼10. We also find that inhomogeneities responsible for the shock formation prior to the collision may produce bulk Compton radiation, which can explain the observed soft X-ray excess and possible excess at ∼18 keV. We note, however, that the bulk Compton interpretation is not unique, as discussed briefly in the text.