Measuring the Coronal Properties of IC4329A with NuSTAR

Abstract

We present an analysis of a ~160 ks NuSTAR observation of the nearby bright Seyfert galaxy IC4329A. The high-quality broadband spectrum enables us to separate the effects of distant reflection from the direct coronal continuum, and to therefore accurately measure the high-energy cutoff to be $E_{cut}=178_{-40}^{+74}$ keV. The coronal emission arises from accretion disk photons Compton up-scattered by a thermal plasma, with the spectral index and cutoff being due to a combination of the finite plasma temperature and optical depth. Applying standard Comptonization models, we measure both physical properties independently using the best signal-to-noise obtained to date in an AGN over the 3-79 keV band. We derive $k{T}_e=37_{-6}^{+7}$ keV with $\ddot{I}„=1.25_{-0.10}^{+0.20}$ assuming a slab geometry for the plasma, and $k{T}_e=33_{-6}^{+6}$ keV with $\ddot{I}„=3.41_{-0.38}^{+0.58}$ for a spherical geometry, with both having an equivalent goodness-of-fit.

17 pages in preprint format, 4 figures, 1 table. Accepted by ApJ