Speaker
Rudy Wijnands
(University of Amsterdam)
Description
I will present our results of our studies on the spectral properties of neutron star low-mass X-ray binaries when they have accretion luminosities between 1e34 and 1e36 erg/s (roughly 0.01 - 1 percent Eddington). We found that their photon index increases with decreasing 0.5-10 keV luminosity (the spectrum softens). Such behaviour has been reported for individual sources, but we now demonstrate that likely most systems behave in a similar manner. When comparing with black-hole systems, it is clear that most black-hole binaries have harder spectra at those luminosities. This suggests that the spectral properties at low luminosities can be used to determine the nature of the accretor in unclassified binaries. We suggest that this difference likely arise from the neutron-star surface becoming dominantly visible. We also suggest that both the thermal component and the non-thermal component might be caused by low-level accretion on the neutron star surface for luminosities below a few times 1e34 erg/s, contrary to the general believe.
Primary author
Rudy Wijnands
(University of Amsterdam)
