Gravity seminar - Mari Kolehmainen Seminar

Black hole spin is a very controversial topic in both stellar and supermassive black holes. There are two methods to determine the spin in binary systems -  either via the extent of broadening of the iron emission line, or from the luminosity and temperature of the accretion disc. These can give significantly different results, and understanding the source of this discrepancy is important especially for interpreting AGN spin, where only the reflection method can be used.

We have strived to understand and carefully model the time-averaged energy spectra from several Galactic black hole binaries, in order to ultimately measure the black hole spin. Problem is the spin leaves only minor traces in the data, and these can be affected by calibration uncertainties, uncertainties in the models and systematic uncertainties. I will present an analysis of all the available XMM-Newton spectra of Galactic black hole binaries at different mass accretion rates, to assess the level of agreement between the spin derived from these two methods.