In Search for coronal temperature variations in Seyfert type active galactic nuclei using NuSTAR

In the standard disc-corona paradigm, the hard X-ray emission in the radio-quiet category of active galactic
nuclei (AGN) is believed to be produced in a hot (~ 10 ^8-9 K) and compact region, the so-called corona. The
hot electrons in the corona, Compton up-scatter thermal optical and ultraviolet photons from the accretion
disc to X-ray energies. The shape of the X-ray continuum, among other factors, depends on the
temperature of the corona (kT_e), which can be probed by broad band X-ray spectral analysis. Investigating
the variation of kT_e with time in individual AGN and examining the correlation of kT_e with X-ray flux and
other parameters e.g. reflection fraction, optical depth etc. could lead to our understanding of the yet
unclear coronal physics in AGN. In this work, we aimed to investigate in a systematic way, the variation of
kT_e in a sample of Seyfert type AGN. We carried out spectral analysis of multiple epochs of data acquired
using the NuSTAR on our sample of sources. By fitting Comptonization models to the data we investigated
the changes in kTe in our sample. We found evidence for variation of kT_e in NGC 3227, 1H0419-577, MRK
915, MCG+08-11-011 and NGC 4258. We also examined the correlations of kTe with other best-fit physical
parameters for this source. In other sources that include among other sources, objects such as MR 2251-
178, NGC 5548 and NGC 1068, we found, no evidence for the variation in kT_e.