A study of the long-term properties of Sco X-1

Representative image for thesis Tutor: Sara Motta
Triennal 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:
Scorpius X-1 the first X-ray source ever discovered outside the Solar System, and also the first example of how accretion onto a compact object can lead to a release of gravitational energy so large and so efficient to produce radiation peaked in the X-rays.
Sco X-1 is a bright X-ray binary hosting a neutron star, which accretes at luminosities close or even exceeding the Eddington limit.
As such, this source is extremely bright in the X-rays, and hence can be easily observed even with instrumentation that are not particularly sensitive, but are able to observe a given source with very high cadence (often several times a day), such as the All Sky Monitors.
A very large dataset obtained with the MAXI mission on board the International Space Station is available for Sco X-1, almost completely unexplored, but which could hide crucial information to understand the behavior and properties of this important system.

The main aim of this thesis is to explore the dataset, with the goal of evidencing properties that only a long-term large database can reveal.
The results obtain via this projects will be contrasted with the known properties of the source (including its multi-wavelength behaviour), and interpreted accordingly.