Hard X-rays from NGC 4151: A thermal origin?

Details Hard X-rays from NGC 4151: A thermal origin? Hard X-rays from NGC 4151: A thermal origin?

Sep 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...433l..33t&link_type=abstract

Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X), vol. 433, no. 1, p. L33-L36

Astronomy and Astrophysics

Astronomy

17

Astronomical Models, Compton Effect, Gamma Ray Spectra, Optical Thickness, Plasma Temperature, Radiative Heat Transfer, Seyfert Galaxies, Space Plasmas, X Ray Spectra, Astronomical Spectroscopy, Gamma Ray Astronomy, Ginga Satellite, Mathematical Models, Power Series, Relativity, Scintillation Counters, X Ray Astronomy

Scientific paper

We present a model for explaining the recent combined X-ray and low-energy gamma-ray observations of the Seyfert galaxy NGC 4151. According to this model, soft photons become Comptonized in a hot spot producing simultaneously the low-energy power law as observed by Ginga and the high-energy cutoff observed by the Oriented Scintillation Spectrometer Experiment (OSSE). Implementing recently developed theoretical calculations toward a generalized theory of Comptonization, we were able to find fits to the observations using only two parameters which characterize the physical quantities of the emission region: the plasma cloud optical depth and its temperature. We find that there is no need for additional nonthermal, reflection, or higher temperature thermal components to fit the aforementioned OSSE and Ginga observations. We derive in addition the size of the photon region and the temperature of the upscattered soft photons. We should emphasize, also, that any attempt at fitting only the high-energy parts of the spectrum (photon energies greater than 60 keV) by the Sunyaev & Titarchuk (1980) nonrelativistic Comptonization model leads to an underestimate of the Comptonization parameter y (or, equivalently, to an overestimation of the X-ray power-law spectral slope) and leads, as a result, to incorrect proportions between the low-energy and high-energy parts of the spectrum.

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