Warm Absorbers in Galactic X-ray Binaries
Norbert S. Schulz (MIT Kavli Institute for Astrophysics & Space Research)
X-ray binaries, specifically the ones labeled as microquasars, are considered to be the small-scale Galactic counterparts of active galactic nuclei (AGN). Physically they are distinctly different in that they are stellar binaries in which a compact object, in most cases a stellar black hole, accretes matter from a stellar companion. These objects exhibit relativistic jets and outflow patterns reminicent of their of their extragalactic cousins. While their radio and X-ray emission indeed provide many signatures that resemble the ones we ususally see in AGNs, they provide an upclose view of the various accretion phenomena common in these objects. This presentation investigates warm absorbers. Until quite recently, warm absorbers were mostly discussed in the context of AGN, but recent observations with high resolution X-ray spectrometers provided a manifold of different warm absorber activity in X-ray binaries, not all of them are considered to actually be microquasars. This presentation reviews recent results involving microquasars (i.e. GROJ1655-40, Cir X-1) and normal X-ray binaries (i.e. 4U 1624-49, EXO 0748-676) with a wide range ionization parameters and column densities. Only recently have we begun to understand and identify warm absorber features which provide novel clues to understand the accretion process onto compact objects.