A brief description of the results obtained in 2008 :
During 2008 (the second year of the project) the research team has focused on a detailed analysis of X-ray emission mechanisms relevant for the ongoing XMM-Newton observations and for future high resolution observations with the International X-ray Observatory (IXO), currently under discussion. The theoretical investigation of avalanche processes in accretion discs was published by Pechacek et al in the European journal of Astronomy and Astrophysics. This work was selected by the journal editors as a highlighted paper and it made a basis of a highly mathematical dissertation, also succesfully defended during 2008. Further, a sequence of two papers appeared in Monthly Notices of the Royal Astronomical Society. Here we examine the aspects of polarization in the context of future X-ray missions. Within the scope of this poject we organized and co-organized three international workshops where the results were discussed.
To briefly summarize our objectives for the year 2008, we have been applying the detailed modeling of physics of accretion disc flares to the analysis of variability X-ray data. To this end we implemented a Monte-Carlo code to sample random distributions of flares across an accretion disc. The radial distribution of flares and their luminosities can be varied by model parameters. The flares are assumed to co-orbit with the accretion disk and have a limited lifetime. They continuously appear and disappear across the disk and their total number fluctuates around the average flare number defined. From such orbiting flare distributions we computed the time evolution of the spectra seen at large distances, thereby including corrections for the Doppler effects and for general relativistic effects in the vicinity of the black hole. Then, variability and time-averaged spectra were computed and compared to the observations. We obtained the `rms' variability, power density, and time-averaged spectra. The model setup can be described by the following global parameters: mass, spin, and accretion rate of the black hole, the fraction of energy dissipated in the disk corona, the illumination structure across the disk. Constraining these main parameters of accreting black holes remains a crucial subject for the X-ray community.
In the year 2009 the continuation of the work will concentrate on joint spectral and polarimetric X-ray characteristics of accretion discs, also in the connection with technology for future missions that are currently under consideration, such as the International X-ray Observatory.
Key papers published of the project team in 2008:
Bursa M. (2008), "High frequency QPO modulation in neutron-star and black-hole sources", New Astronomy Reviews, 51, 846-854
Dovčiak M., Karas V., Matt G., Goosmann R. W. (2008), "Variation in the primary and reprocessed radiation from an orbiting spot around a black hole", Monthly Notices of the Royal Astronomical Society, 384, 361-369
Dovčiak M., Muleri F., Goosmann R., Karas V., Matt G. (2008), "Thermal disc emission from a rotating black hole: X-ray polarization signatures", Monthly Notices of the Royal Astronomical Society, 391, 32-38
Pecháček T., Karas V., Czerny B. (2008): "Hot-spot model for accretion disc variability as random process", Astronomy and Astrophysics, 487, 815-830
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