Suzaku Observations of Extreme MeV Blazar SWIFT J0746.3+2548

TL;DR

This paper presents Suzaku X-ray observations of the high-redshift blazar SWIFT J0746.3+2548, revealing an extremely hard spectrum and analyzing its multiwavelength emission to understand jet physics and pair content.

Contribution

It provides the first Suzaku high-energy spectrum of this distant blazar and investigates the presence of bulk Compton features to constrain jet composition.

Findings

Confirmed a very hard X-ray spectrum with photon index 1.17

Modeled the spectral energy distribution with Comptonization of broad-line region photons

Set constraints on pair content due to absence of expected bulk Compton features

Abstract

We report the Suzaku observations of the high luminosity blazar SWIFT J0746.3+2548 (J0746) conducted in November 2005. This object, with z = 2.979, is the highest redshift source observed in the Suzaku Guaranteed Time Observer (GTO) period, is likely to show high gamma-ray flux peaking in the MeV range. As a result of the good photon statistics and high signal-to-noise ratio spectrum, the $Suzaku$ observation clearly confirms that J0746 has an extremely hard spectrum in the energy range of 0.3-24 keV, which is well represented by a single power-law with a photon index of 1.17 and Galactic absorption. The multiwavelength spectral energy distribution of J0746 shows two continuum components, and is well modeled assuming that the high-energy spectral component results from Comptonization of the broad-line region photons. In this paper we search for the bulk Compton spectral features predicted to be produced in the soft X-ray band by scattering external optical/UV photons by cold electrons in a relativistic jet. We discuss and provide constraints on the pair content resulting from the apparent absence of such features.