Origin of multiwavelength emission from flaring high redshift blazar PKS 0537-286

TL;DR

This study analyzes multiwavelength data of high-redshift blazar PKS 0537-286, revealing flaring activity, spectral hardening, and jet emission characteristics, providing insights into relativistic jet physics in early universe quasars.

Contribution

It presents a detailed multi-frequency spectral and temporal analysis of PKS 0537-286, modeling its emission during quiescent and flaring states within a one-zone leptonic framework, highlighting the emission region's location.

Findings

Flares show increased luminosity and spectral hardening.

Jet energy dissipation likely occurs within the broad-line region.

Flaring caused by electron spectral hardening and higher cutoff energy.

Abstract

The high redhsift blazars powered by supermassive black holes with masses exceeding $10^9\:M_\odot$ have the highest jet power and luminosity and are important probes to test the physics of relativistic jets at the early epochs of the Universe. We present a multi-frequency spectral and temporal study of high redshift blazar PKS 0537-286 by analyzing data from Fermi-LAT, NuSTAR Swift XRT and UVOT. Although the time averaged $\gamma$-ray spectrum of the source is relatively soft (indicating the high-energy emission peak is below the GeV range), several prominent flares were observed when the spectrum hardened and the luminosity increased above $10^{49}\:{\rm erg\:s^{-1}}$. The X-ray emission of the source varies in different observations and is characterised by a hard spectrum $\leq1.38$ with a luminosity of $>10^{47}\:{\rm erg\:s^{-1}}$. The broadband spectral energy distribution in the quiescent and flaring periods was modeled within a one-zone leptonic scenario assuming different locations of the emission region and considering both internal (synchrotron radiation) and external (from the disk, broad-line region and dusty torus) photon fields for the inverse Compton scattering. The modeling shows that the most optimistic scenario, from the energy requirement point of view, is when the jet energy dissipation occurs within the broad-line region. The comparison of the model parameters obtained for the quiescent and flaring periods suggests that the flaring activities are most likely caused by the hardening of the emitting electron spectral index and shifting of the cut-off energy to higher values.