Accretion flow properties in low-mass X-ray binaries

PhD ceremony: Mr. A. Sanna, 11.00 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Accretion flow properties in low-mass X-ray binaries

Promotor(s): prof. R.M. Mendez

Faculty: Mathematics and Natural Sciences

In this thesis I investigate the accretion flow properties in low-mass X-ray binaries (LMXBs), in which a neutron star or a stellar-mass black hole accretes matter from a low-mass companion star via an accretion disc.

X-ray binaries are unique laboratories that allow us to investigate the physics of strong gravity and dense matter in extreme conditions not reproducible on Earth. General relativity effects around these compact objects are orders of magnitude stronger than those for which general relativity has been successfully tested (weak-field regime).

The exact nature of the elementary particles that form a neutron star (NS), as well as their collective properties, are still not well understood to predict the equations describing the state of the matter of these objects. By investigating the orbital motion around a NS, both the NS mass and radius can be constrained, which can be used to determine the equation of the state, hence the fundamental properties of the matter inside NSs.

In order to understand X-ray binaries we study the photons emitted by these systems. In this work I focus on the X-ray emission that originates in the surroundings of the compact object. Currently we cannot resolve the LMXBs using direct imaging techniques in X-ray, therefore the spectral and timing studies are the main techniques we use to understand the source spectral evolution and to re- veal its physical parameters. Of particular interest for this work is the study of the kilohertz quasi-periodic oscillations (kHz QPOs) and the relativistic iron emission lines, that represent timing and spectral properties of the LMXBs, respectively.