Multi-wavelength temporal and spectral study of PKS 0402-362

TL;DR

This study analyzes 12.5 years of multi-wavelength data of the gamma-ray blazar PKS 0402-362, revealing its flaring behavior, spectral characteristics, and the connection between the accretion disk and jet using a one-zone leptonic model.

Contribution

It provides the first detailed long-term multi-wavelength analysis of PKS 0402-362, modeling its broadband SED with a simple one-zone leptonic approach and linking disk and jet emissions.

Findings

Identified three gamma-ray activity periods with the highest brightness observed.

Most gamma-ray flares show asymmetric profiles, suggesting slow particle cooling or Doppler factor variations.

Spectral analysis indicates steep spectral indices and no time lag between optical-IR and gamma-ray emissions.

Abstract

We study the long-term behavior of the bright gamma-ray blazar PKS 0402-362. Over a span of approximately 12.5 years, from August 2008 to January 2021, we gathered Fermi-LAT temporal data and identified three distinct periods of intense $\gamma$-ray activity. Notably, the second period exhibited the highest brightness ever observed in this particular source. We observed most of the $\gamma$-ray flare peaks to be asymmetric in profile suggesting a slow cooling time of particles or the varying Doppler factor as the main cause of these flares. The $\gamma$-ray spectrum is fitted with power-law and log-parabola models, and in both cases, the spectral index is very steep. The lack of time lags between optical-IR and $\gamma$-ray emissions indicates the presence of a single-zone emission model. Using this information, we modeled the broadband SEDs with a simple one-zone leptonic model using the publicly available code `GAMERA'. The particle distribution index is found to be the same as expected in diffusive shock acceleration suggesting it as the main mechanism of particle acceleration to very high energy up to 4 - 6 GeV. During the different flux phases, we observed that the thermal disk dominates the optical emission, indicating that this source presents a valuable opportunity to investigate the connection between the disk and the jet.