Fundamental Properties of Accreting Compact Objects.

Abstract

Galactic accreting compact objects, such as stellar-mass black holes and neutron stars, can give us a unique perspective into the behavior of matter in extreme conditions. However, the exact nature of accretion onto these objects is not yet well understood. X-ray studies provide us with a means to observe the innermost regions around these objects and to explore our theories of general relativistic physics. Through X-ray analyses we can constrain the physical parameters necessary to make logical deductions regarding compact object properties, such as disk winds, relativistic jets, the Kerr metric, and the neutron star equation of state.

Here we present spectral modeling results from three accreting X-ray binaries. Specifically, we analyze Suzaku spectra from two stellar-mass black hole X-ray binaries, GRS 1915+105 and H1743-322, and one neutron star X-ray binary, 4U 1636-53. For GRS 1915+105 and 4U 1636-53, we use the relativistic iron line, which is part of a reflection spectrum, as a diagnostic for measuring black hole spin and neutron star radius, respectively. We find that while we can exclude a spin of zero at the 2 sigma level of confidence for GRS 1915+105, data selection and disk reflection modeling nuances can be important when estimating the spin value. For 4U 1636-53, we provide upper limits on the neutron star radius by estimating the radial extent of the inner accretion disk, which are important for constraining models for the neutron star equation of state. Moreover, when testing for the presence of disk winds in H1743-322 (which are key to understanding the nature of accretion disk outflow), we do not detect Fe XXV or Fe XXVI absorption lines in its spectra of H1743-322; implying that disk winds may be state dependent.