Maciej Wielgus (Center for Astrophysics | Harvard & Smithsonian)
A widely accepted picture of an accretion flow in a soft spectral state X-ray binary is a geometrically thin disk structure much alike the classic analytic solution of Shakura & Sunyaev. Despite the fact that the analytic models are troubled by instabilities and miss important aspects of physics such as magnetic fields, they are commonly and successfully used as a framework for interpreting the observational data through spectral fitting. The thin disk model applicability to observational data analysis breaks for luminosities > 0.3 Eddington luminosity, when disk becomes thicker and advection becomes appreciable. In recent years global relativistic radiative magnetohydrodynamic simulations have reached sufficient maturity to probe the regime of optically thick accretion with a mildly sub-Eddington luminosity. These simulations find the accretion flow stabilized by the magnetic field, with a dense geometrically thin core and a puffed-up optically thick region around it, reaching h/r of ~1 for half of the Eddington luminosity. Interactions between the magnetic field and radiation create a non-trivial vertical structure of the flow, that is not captured by the (semi)analytic models. I will discuss these recent simulations and their potential observational implications, including the collimation effects, and influence on the spectra.
People from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Stanislaw Bajtlik at: bajtlik@camk.edu.pl
Andrzej Zdziarski (CAMK, Warsaw)
I will present a number of results related to the relative importance of relativistic effects in accreting flows onto black holes. In particular, I will review the current evidence for and against the accretion disc extending to the innermost stable circular orbit (ISCO) in the hard spectral states of black-hole binaries. The spectral and timing results of our group imply the discs are significantly truncated away from the ISCO in the hard state. Especially, a recent result of Zdziarski & De Marco (arXiv:2002.04652) rules out the presence of a disc near the ISCO in luminous hard states based on the Stefan-Boltzmann law. On the other hand, the majority of currently published papers claim the disc is extending to the ISCO and very strongly irradiated.
People from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Stanislaw Bajtlik at: bajtlik@camk.edu.pl
John Beckman (Instituto de Astrofísica de Canarias)
In our research group we have built and used a Fabry-Perot interferometer which, on the 4.2m William Herschel Telescope at the IAC Observatory on La Palma, gives two-dimensional velocity maps of galaxies using the Halpha emission from the interstellar medium. The maps have a wide field (3.4 x3.4 arcminutes), with seeing-limited spatial resolution below 1 arcsecond and velocity resolution of order 6 km/s across the full field. With these maps we have devised an accurate method for determining the corotation radius of a density wave pattern in a galactic disc. Applying the method we find that the discs have multiple corotation radii: the density waves are confined in separate annular regions, not necessarily related to the galactic bar. These results are being applied to a number of problems: whether galactic bars are being slowed down by dynamical friction with dark matter halos; whether swing amplification or manifold scenarios give a better account of the generation of the spiral arms; what determines the numbers and the bifurcations in the arms. My talk will give an overview of this subject, and present the latest results.
People from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Stanislaw Bajtlik at: bajtlik@camk.edu.pl
Tomasz Kamiński (CAMK, Toruń)
People from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Stanislaw Bajtlik at: bajtlik@camk.edu.pl
