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Simultaneous radio and X-ray observations of X-ray binaries with MeerKAT and Swift

Representative image for thesis Tutor: Sara Motta
Master’s Thesis

Background - X-ray binaries:
Throughout the Universe the combination of a deep potential well and an accretion disc, (which forms when matter is gravitationally captured by a celestial body) leads to the generation of fast, collimated outflows called jets.
This process, still poorly understood, occurs in proto-planetary discs and at the centre of galaxies alike, but around black hole (BHs) and neutron stars (NSs) it is taken to the extreme.
In a process known as feedback these so-called compact objects contrive to feed back to the surrounding space a large fraction of the energy and matter they could have swallowed, thereby acting to heat their environment rather than behaving only as sinks.
Feedback is important across a range of scales: from stellar-mass BHs and NSs in X-ray binaries (XRBs), to super-massive BHs powering the AGN, which via this process regulated the growth of massive galaxies.
The AGN and XRBs hosting BHs and NSs provide us with the best tests of General Relativity, but while the former evolve over decades to millenia, XRBs evolve rapidly, offering us the opportunity to probe on humanly accessible time-scales the energy and matter input/output around accreting objects.
The knowledge gained from studying XRBs can then be directly applied to AGN, where the inflow/outflow processes follow the same basic principles as around stellar-mass BHs.

Using observations from across the entire electromagnetic spectrum, and employing various techniques best-suited to extract the information stored in the data we investigate the physics of the accretion and outflow generation processes in X-ray binaries, with the aim of understanding the nature of such processes and the link between them both on stellar-mass scales, and on super-massive scales.

The Thesis:
The MeerKAT radio telescope is a large interferometer located in South-Africa, dedicated to the study of the radio sky between 1 and 4 GHz.
MeerKAT is one of the pathfinder for SKA, which will sign a new era of radio astronomy, characterized by high cadence, high sensitivity radio observations of the entire sky at moderate angular resolutions.
As part of the ThunderKAT project, which is dedicated to the study of both Galactic and extra-Galactic radio transients, we observe weekly interesting X-ray binaries located in the Southern Sky when they become active.
Simultaneous observations are taken with the Swift Observatory via the SwiftKAT large program (PI: S. E. Motta).

The aim of this thesis is to study both in radio and in the X-rays simultaneously a new outburst of a X-ray binary (either hosting a neutron star or a black hole) using brand new proprietary data collected with the MeerKAT radio telescope, and simultaneous X-ray data obtained with Swift.
We will extract radio images from the MeerKAT data, which may reveal the presence of transient relativistic jets which evolve over time.
The variations in the radio properties of the X-ray binary will be interpreted together with the results form the Swift light curves and energy spectra, with the aim of investigating the accretion-ejection coupling in the target.
The results will be then put in context of what is known of accreting compact objects, both stellar mass and super-massive.