X-ray spectral index correlations vs mass accretion rate in neutron star and black hole X-ray binaries in their different spectral states. Theory vs observations

start date: 

Mercredi, octobre 25, 2017 - 14:00

Place: 

salle 483A

Speaker: 

Lev Titarchuk

Home Institute: 

University of Ferrara and Goddard Space Flight Center

organized by: 

I present  details  of observations of neutron star (NS) and black hole (BH) binaries and the first principle theory of X-ray spectral formation in neutron star (NS) and black hole (BH) there.  I show that this model predicts the spectral index correlation vs mass accretion rate  as in the case of NS as well in the BH case.  In BHs the spectral index should increase and then saturate with mass accretion rate, because the index is an inverse  of Comptonization parameter Y and  Y-parameter saturates with the high mass accretion rate in the converging flow onto BH. Comparison of this model prediction with X-ray  observations shows that  in a BH case the index, indeed, correlates and then saturates with mass accretion rate.
Moreover this index-mass accretion rate correlation allows us to estimate BH masses and distance to the source.  While in NS sources, the observations show that  the index stays the same independently of spectral state of the source which can be possible if the energy release in the disk is always much smaller of that at NS TL (boundary layer).