A Unification Scheme for the Spectral States of the Galactic Black Hole Cyg X-1

Details A Unification Scheme for the Spectral States of the Galactic Black Hole Cyg X-1 A Unification Scheme for the Spectral States of the Galactic Black Hole Cyg X-1

Apr 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998aps..apr..r809c&link_type=abstract

American Physical Society, APS/AAPT Joint April Meeting, April 18-21, 1998 Columbus, Ohio, abstract #R8.09

Physics

Scientific paper

Several galactic black hole systems show transitions between different spectral states. Here we concentrate on the object Cyg X-1 for which good, broad-band spectral data from ~ 1 keV to 4 MeV is available. We fit the data for the individual ``hard" and ``soft" states of Cyg X-1 using an emission model where a central Comptonizing corona/cloud is illuminated by the soft photon emission from a cold disk. We assume that energy is effectively injected into a corona above the disk via two channels: a non-thermal one that injects energetic electrons into the coronal region, and a thermal one that heats injected and ambient electrons once they cool sufficiently to form a Maxwellian distribution, i.e., we consider a hybrid thermal/non-thermal model. The same emission model (albeit with different parameters) gives excellent fits to the data in both states. Using simple scaling laws for the luminosity of the cold disk, the thermal dissipation/heating rate in the corona, and the rate of energy injection from a non-thermal source, all as functions of radius of the corona, we can explain the hard-to-soft transition as the result of a decrease in the size of the corona and the inner radius of the cold disk by a factor ~ 5. We show that the bolometric luminosity of the source (mass accretion rate) does not change significantly during the transition, i.e., the transition probably results from a disk instability.

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