Testing Comptonizing Coronae on a Long BEPPOSAX Observation of the Seyfert 1 Galaxy NGC 5548

Abstract

We test accurate models of Comptonization spectra over the high-quality data of the BeppoSAX long look at NGC 5548, allowing for different geometries of the scattering region, different temperatures of the input soft photon field, and different viewing angles. We find that the BeppoSAX data are well represented by a plane-parallel or hemispherical corona viewed at an inclination angle of 30°. For both geometries the best-fit temperature of the soft photons is close to 15 +3 -9 eV. The corresponding best-fit values of the hot plasma temperature and optical depth are kT e ~=250-260 keV and τ~=0.16-0.37 for the slab and hemisphere, respectively. These values are substantially different from those derived fitting the data with a power-law-plus-cutoff approximation to the Comptonization component (kT e e in the high state.