6th FERO meeting

ASTRONOMICAL INSTITUTE
ACADEMY OF SCIENCES, PRAGUE
Boční II 1401, 141 00 Praha 4
Czech Republic

30th – 31st of August 2012



Euro in Czech Crowns: 1€ = Kč
Metro-Tram scheme
Map of centre (more detailed)
    Participants

August



Michal Bursa

X-ray continuum fitting of accretion disc spectra

[presentation]

Fitting of X-ray continuum has become a powerful way of measuring black hole spins in stellar mass X-ray binaries. Still, a good caution needs to be taken when analyzing observation data. In case of almost every black-hole X-ray binary where BH spin has been estimated using this method, the result shows a drop of the estimated spin with increasing luminosity after luminosity exceeds a treshold value of ~0.3 Eddington. This tells us that the accretion disc model that has been used (Novikov-Thorne thin disc) starts to have difficulties to accurately describe the real disc spectra, which are significantly softer than the one predicted by the model. However, it is not only the disc model which shapes the final spectrum. Equally important is the spectral hardening predicted by disc atmosphere models (e.g. BHSPEC). The talk will summarize the basics of the fittig method, processes that modify emergent spectrum of thermal discs and depart it from being blackbody. It will show the effects of spectral hardening factor, its dependence on luminosity and alpha-viscosity and implications for spectral fittings.