Evidence for coronal temperature variation in Seyfert 2 ESO 103--035 using NuSTAR observations

TL;DR

This study analyzes NuSTAR observations of Seyfert 2 galaxy ESO 103--035, revealing that its coronal temperature increases with flux, contrasting previous findings in other AGN, and suggesting different variability mechanisms.

Contribution

First to report flux-dependent coronal temperature variation in ESO 103--035 using NuSTAR data with thermal Comptonization modeling.

Findings

Coronal temperature increases from ~24 keV to ~55 keV with flux.

Contrasts with previous AGN where temperature decreased with flux.

Supports variability driven by coronal heating or seed photon flux changes.

Abstract

We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103--035 using \textit{NuSTAR} observations. Following an earlier work, we fit the spectra using a thermal Comptonization model with a relativistic reflection component to obtain estimates of the coronal temperature for two flux levels. The coronal temperature was found to increase from 24.0$^{+6.8}_{-3.4}$ to 55.3$^{+54.6}_{-7.2}$ keV (errors at 1-$\sigma$ confidence level) as the flux increased from $9.8$ to $11.9 \times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ in the 3--78 keV band. A marginal variation in the high energy photon index allows for both, a non-varying optical depth and for the optical depth to have varied by a factor of $\sim$2. This is in contrast to a previous work on \textit{NuSTAR} flux resolved spectroscopy of the AGN, Ark 564, where the temperature was found to decrease with flux along with a $10$\% variation in the optical depth. The results maybe understood in a framework where AGN variability is either dominated by coronal heating variation leading to correlated increase of temperature with flux and the opposite effect being seen when the variability is dominated by changes in the seed photon flux.