Measuring the Coronal Properties of IC4329A with NuSTAR

L. W. Brenneman, G. Madejski, F. Fuerst, G. Matt, M. Elvis, F. A. Harrison, D. R. Ballantyne, S. E. Boggs, F. E. Christensen, W. W. Craig, A. C. Fabian, B. W. Grefenstette, C. J. Hailey, K. K. Madsen, A. Marinucci, E. Rivers, D. Stern, D. J. Walton, W. W. Zhang

Published 2013-12-12Version 1

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 $E_{cut}=178^{+74}_{-40}$ 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 $kT_e=37^{+7}_{-6}$ keV with $\tau=1.25^{+0.20}_{-0.10}$ assuming a slab geometry for the plasma, and $kT_e=33^{+6}_{-6}$ keV with $\tau=3.41^{+0.58}_{-0.38}$ for a spherical geometry, with both having an equivalent goodness-of-fit.