EDP Sciences
Free access
Volume 387, Number 3, June I 2002
Page(s) 907 - 917
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020293

A&A 387, 907-917 (2002)
DOI: 10.1051/0004-6361:20020293

X-ray spectra from accretion disks illuminated by protons

B. Deufel, C. P. Dullemond and H. C. Spruit

Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstr. 1, 85740 Garching, Germany

(Received 31 August 2001 / Accepted 26 February 2002 )

The X-ray spectrum from a cool accretion disk heated by virialized protons is computed. The cool disk is either embedded in a magnetically heated accretion disk corona or partly extends into an ion supported torus (or ADAF). We calculate the stationary equilibrium between proton heating, electron thermal conduction and the radiative losses by bremsstrahlung and Compton scattering. A heated surface layer on top of the accretion disk is produced with temperatures between 60-90 keV above a cool layer with temperatures of 0.01 keV (AGN) and 1 keV (galactic black hole candidates). The spectra produced by the surface layer are reminiscent of hard state spectra, but a bit too steep, especially for AGN's. Near the inner edge of the disk, where the optical depth of the disk $\tau \lesssim 1$, we find that the cool component of the disk disappears. Instead, the hot protons from the corona/ADAF heat the disk, on a dynamical time-scale, to temperatures of several 100 keV, limited by pair production. This region, here called a "warm disk", could contribute significantly to the hard X-ray spectra and could be important for feeding material into an ADAF.

Key words: accretion, accretion disks -- black hole physics -- X-rays: galaxies -- X-rays: stars

Offprint request: B. Deufel, bed@mpa-garching.mpg.de

© ESO 2002