Martina Veresvarska

Research

My research focuses on testing accretion mechanisms and their scaling variance. Accretion, the process by which matter accumulates onto a compact object, is vital for energy generation in various astrophysical systems. These systems range from white dwarfs, neutron stars, and black holes in X-ray binaries to protostars in young stellar objects and supermassive black holes in active galactic nuclei. A key feature shared by these objects is the presence of an accretion disc formed around the central compact object. However, the standard disc model often struggles to explain certain observations, particularly in the inner regions close to the compact object. Accreting white dwarfs are especially useful for studying accretion physics. Their relatively small size excludes relativistic effects, and their low-radiation environments allow for observations in optical wavelengths, which is often not possible for supermassive black holes due to the ultraviolet-heavy radiation field. To explore the inner workings of accretion flows, I analyse how the brightness of these systems changes over time, using data from space-based telescopes such as TESS and Kepler in the optical range, and XMM-Newton in the X-ray range. These brightness variations can reveal critical patterns in the behaviour of the accretion flow.

Studying broad-band variability power spectra of accreting systems is essential in understanding the geometry of the accretion disc. Using optical long term photometry such as TESS and Kepler allows probing of new timescales to greater depth. With Kepler we were able to tentatively probe the outer regions of the accretion disc in the most compact of system, such as the LISA verification binary SDSS J1908+3940 above. It shows a clear decrease of power at the low frequencies indicating vicinity of the accretion disc edge. Upcoming missions like PLATO will enable constraining similar and more detailed pictures of the accretion disc in much larger systems.

TESS also provides unprecedented view of periodic and quasi-periodic variability of accreting white dwarfs. Recently we have discovered a new type of quai-periodic oscillations (QPOs) in TESS observations of accreting white dwars that show direct analogy to well known QPOs in X-ray binaries. We propose that these QPOs are a results of a precessing inner flow of the accretion disc which is lifted up by the moderately strong magnetic field of the white dwarf, but not strong enough to create a magnetically confined accretion stream as observed in some cases. These newly discovered QPOs also follow the same linnear correlation as the X-ray binary QPOs, showcasing the scalability of accretion across all types of accreting objects.

With much of the TESS data still waiting to be leveraged to its full potential there is still much we can learn about accretion physics from accreting white dwarfs. In my recent study of the systematic broad band variability in TESS we have shown that the broad band structure is highly depenedent on the accretion rate and disc viscosity, outlining a clear difference in accretion disc structure for different types of accreting white dwarfs.

Publications

You can find a list of my first author and co-authored publications below or in this ADS library here

CV

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