# Exploring the origin of multiwavelength activities of high-redshift FSRQ PKS 1502+106 during 2014-2018

## TL;DR

This study investigates the origins of multiwavelength flares in high-redshift FSRQ PKS 1502+106, revealing magnetic reconnection and shock processes as key triggers through detailed analysis of gamma-ray and optical data.

## Contribution

It provides the first detailed multi-band analysis of PKS 1502+106's flares, constraining physical parameters and proposing magnetic reconnection and shock as mechanisms.

## Key findings

- Discovered a 1-hour gamma-ray flare with spectral hardening.
- Linked optical polarization to shock compression during 2017 outburst.
- Constrained emission region size and magnetic field strength.

## Abstract

The origin of the multi-band activities (outbursts/flares) of blazars is still a heavily debated topic. Shock and magnetic reconnection have long been considered as possible triggers for the multi-band activities. In this paper, we present an exploration of the origin of multi-band activities for a high-redshift (z =1.8385) FSRQ PKS 1502+106. Utilizing multi-band data from radio to $\gamma$-ray and optical polarization observations, we investigate two dramatic activities in detail: a $\gamma$-ray dominated outburst in 2015 and an optical dominated outburst in 2017. Our main results are as follows. (I) A fast $\gamma$-ray flare with a flux-doubling time-scale as short as 1-hr in 2015 is discovered. Based on the variability time-scale, the physical parameters of the flaring region (e.g, minimum Doppler factor, emission region size, etc.) are constrained. At the peak of the flare, the $\gamma$-ray spectrum hardens to $\Gamma_{\gamma} = 1.82\pm0.04$ and exhibits an obvious curvature/break characteristic that is caused by the typical "cooling break". Modelings of multi-band SEDs reveal a very hard electronic energy spectrum with the electronic spectral index of $1.07\pm0.53$. This result suggests that this fast $\gamma$-ray flare may be triggered by magnetic reconnection. (II) During the outburst in 2017, the optical polarization degree and optical fluxes show a very tight correlation. By analyzing Stokes parameters of polarization observations, our results show that this outburst could be triggered by a transverse shock with a compression ratio of $\eta> 2.2$, and the magnetic field intensity of the shock emission region is about $0.032$ G.