MEASURING THE CORONAL PROPERTIES OF IC 4329A WITH NuSTAR

We present an analysis of a similar to 160 ks NuSTAR observation of the nearby bright Seyfert galaxy IC 4329A. 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 active galactic nucleus over the 3-79 keV band. We derive kTe = 37+ 6 keV with tau = 1.25(-0.10)(+0.20) assuming a slab geometry for the plasma, and kT(e) = 33(-6)(+6) keV with tau = 3.41(-0.38)(+0.58) for a spherical geometry, with both having an equivalent goodness-of-fit.