2021ApJ...921...46B

We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103-035 using 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_–3.4^+6.8 to 55.3_–7.2^+54.6keV (errors at the 1σ confidence level) as the flux increased from 9.8 to 11.9 x 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 nonvarying optical depth and for the optical depth to have varied by a factor of ∼2. This is in contrast to a previous work on 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 may be understood in a framework where AGN variability is either dominated by coronal heating variation leading to a correlated increase of temperature with flux or the opposite effect being seen when the variability is dominated by changes in the seed photon flux.