Mehmet Hakan Erkut - June 9, 2017

High-frequency oscillations from accreting neutron stars and black holes in our galaxy

Since the discovery of the first extrasolar cosmic X-ray source, Scorpius X-1,
in 1962, neutron stars and stellar-mass black holes accreting gaseous material
from their normal companions in binaries have become the subject of a
long-standing active area of research in high-energy astrophysics. Within three
years after the launch of Rossi X-ray Timing Explorer, high-frequency
oscillations have been discovered in the X-ray power spectra of neutron stars
and black holes in low-mass X-ray binaries (LMXBs). A typical LMXB consists of
either a weakly magnetized neutron star or a black hole accreting mass from a
Roche lobe filling late type normal star of mass less than or similar to one
solar mass. High-frequency oscillations include burst oscillations, kilohertz
(kHz) quasi-periodic oscillations (QPOs), and millisecond pulsations in
neutron-star sources, and hectohertz QPOs in black-hole sources. In the present
talk, we briefly summarize the observational properties of the high-frequency
oscillations from the galactic LMXBs. We mainly focus on the high-frequency QPOs
from neutron stars and black holes, and discuss the relevance of these
oscillations to the physics of strong gravity and dense matter. Finally, we
present the results of our recent work on the modeling of the high-frequency
QPOs in terms of the global oscillatory modes in the innermost region of the
accretion disk around the compact object.