Speaker: Dr. Robert Soria (Mullard Space Science Laboratory, University of College London) 
Time: 2:00PM, Sept. 5th (Friday)
Location: Middle Conference room, 3rd floor
 
Abstract: 
Spectral state transitions from accreting black holes (BHs) are an indirect way to estimate the mass accretion rate and the BH mass. Stellar-mass BHs tend to be dominated by a thermal disk (disk-blackboby spectrum)  when they are in a luminous state, and a Comptonizing region (power-law spectrum) at lower accretion rates. Ultraluminous X-ray sources (ULXs) show different states, and do not seem to have a pure disk state. It is not clear whether this is due to a fundamental difference in the accreting BH mass, the mass transfer rate, or the type of donor star. It is also unclear whether AGN accretion states are more similar to those of stellar-mass BHs or ULXs.