Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-04-10
Astronomy and Astrophysics
Astrophysics
4 pages, 2 figures, to appear in the proceedings of the conference "X-ray Astronomy '99", Bologna, Italy, September 1999
Scientific paper
10.1063/1.1434664
We test accurate models of Comptonization spectra over the high quality data of the BeppoSAX long look at NGC 5548. The data are well represented by a plane parallel corona with an inclination angle of 30$^{\circ}$, a soft photon temperature of 5 eV and a hot plasma temperature and optical depth of $kT_{\rm e}\simeq$ 360 keV and $\tau\simeq$ 0.1, respectively. If energy balance applies, such values suggest that a more ``photon-starved'' geometry (e.g. a hemispheric region) is necessary. The spectral softening detected during a flare, appears to be associated to a decrease of the heating-to-cooling ratio, indicating a geometric and/or energetic modification of the disk plus corona system. The hot plasma temperature derived with the models above is significantly higher than that obtained fitting the same data with a power law plus high energy cut off model for the continuum. This is due to the fact that in anisotropic geometries Comptonization spectra show "intrinsic" curvature which moves the fitted high energy cut-off to higher energies.
Grandi Paola
Haardt Francesco
Maraschi Laura
Matt Giorgia
Nicastro Fabrizio
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