X-Ray/Soft Gamma-Ray Observation of Centaurus A and Its Implication on the Emission Mechanism

Details X-Ray/Soft Gamma-Ray Observation of Centaurus A and Its Implication on the Emission Mechanism X-Ray/Soft Gamma-Ray Observation of Centaurus A and Its Implication on the Emission Mechanism

Dec 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996pasj...48..801m&link_type=abstract

Publications of the Astronomical Society of Japan, v.48, p.801-811.

Astronomy and Astrophysics

Astronomy

18

Galaxies: Individual (Centaurus A), Galaxies: Radio, Gamma Rays: Observations

Scientific paper

We have studied Cen A (NGC 5128) in the X-ray band (3--20 keV) and soft gamma -ray band (40--600 keV) with the Large Area Counter (LAC) of the Ginga satellite (1989 March and 1990 February) and with a balloon-borne low background detector (Welcome-1, 1991 November), respectively. The observed continuous spectra show a power-law shape (Gamma ~ 1.8) with relatively heavy absorption (N_H ~ 1.5 times 10(23) H cm(-2) ) at the low-energy end and a possible break at ~ 180 keV. We analyzed the total spectra as the sum of the direct power-law flux from the central engine, the Compton-scattered flux from a cold cloud near to the engine, and the iron fluorescence-line flux. By assuming that the geometry around the central engine remained unchanged during the two-year period, we studied two possible cold cloud geometries by comparing Monte-Carlo simulations with our observations: the first is the Compton-reflection model in which the cloud forms a slab covering 2pi sr behind the central engine, the second is a case where the central source is totally surrounded by a cold cloud. We found that the latter geometry reproduces our data well; the observed power-law spectrum is then identified as direct flux from the central engine which undergoes a break at ~ 180 keV.

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