Multiwavelength Observations of the Powerful Gamma-ray Quasar PKS 1510-089: Clues on the Jet Composition

TL;DR

This study presents multiwavelength observations of the gamma-ray quasar PKS 1510-089, revealing complex spectral features and variability, and models the jet emission suggesting a proton-dominated jet with electron-positron excess.

Contribution

It provides the first detailed broadband spectral analysis of PKS 1510-089 combining Suzaku, Swift, optical, and radio data, and proposes a comprehensive jet emission model including bulk-Compton radiation.

Findings

The X-ray spectrum is extremely hard with a photon index ~1.2.

The soft X-ray excess can be explained by bulk-Compton radiation or alternative processes.

Jet power is proton-dominated with an electron-positron excess by a factor of ~10.

Abstract

We present the results from a multiwavelength campaign of the powerful Gamma-ray quasar PKS 1510-089. This campaign commenced with a deep Suzaku observation lasting three 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 broad-band spectral energy distribution from 10^9 Hz to 10^{19} Hz. The Suzaku observation provided a high S/N X-ray spectrum, which is well represented by an extremely hard power-law with photon index Gamma ~ 1.2, augmented by a soft component apparent below 1 keV, which is well described by a black-body model with temperature kT ~ 0.2 keV. Monitoring by Suzaku revealed temporal variability which is different 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 of PKS 1510-089 assuming that the high energy spectral component results from Comptonization of infrared radiation produced by hot dust located in the surrounding molecular torus. In the adopted internal shock scenario, the derived model parameters imply that the power of the jet is dominated by protons but with a number of electrons/positrons exceeding a number of protons by a factor ~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, and the observed soft excess could arise as well via some other processes discussed briefly in the text.