Fast variability in accretion systems research group

CATACLYSMIC VARIABLES:

We are interested in fast stochastic variability (the so called flickering) generated by accretion process in cataclysmic variables. Mainly those with disc interest us. This dynamic photometric behaviour brings all informations about the accretion geometry and individual substructures of the flow. The most exciting is the very central region close to the central compact star radiating in X-rays. For this research we use optical data taken by Kepler satelite (example) and X-ray observatory XMM-Newton (example). We search for characteristic frequencies in the light curves with the goal to localise the physical source of the variability (example). For the latter we distinguish radiation source and the original fluctuation source, i.e. a mass accretion fluctuation generated at the outer accretion disc propagates inwards and liberates radiation at the inner disc boundary. We use also non-standard methods like averaged shot profile of fast variability where we can study directly individual substructures of the fast variability not distinguishable with for example Fourier based methods (example).

Our team is very signal oriented. Besides flickering we are interested in periodic or quasiperiodic oscillations in short satellite light curves with all the periodogram artifacts (example). Monte Carlo simulations are very usefull here (example). We collaborate with our partners on novae variability and we use data from XMM-Newton and Chandra (example). The goal is to identify spin of the white dwarf or pulsations in the hydrogen burning layer. The periodograms are sometimes very complicated and various effects produce annoying artifacts (example). Such problematic periodogram can yield to wrong interpretation.

 

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MORE EXOTIC OBJECTS:

As cataclysmic variables are accretion powered systems like X-ray binaries or AGNs, we do not refuse to look farther. We analysed fast variability of AGNs present in the Kepler field in order to search for multicomponent nature of the flickering (example). Swift X-ray data were also very useful in this case. So far we studied instrumental effects strongly contaminating AGN observations by Kepler (example). We search for common accretion finger-prints in cataclysmic variables and AGNs. We found very similar averaged shot profile morphology in three types of accreting objects; cataclysmic variable, X-ray binary and a blazar (example).

 

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THE TEAM:

Pavol Bezák      researcher, signal analysis, periodic variability
Dominika Janíková      researcher, signal analysis, stochastic variability
Denis Benka      PhD student, signal analysis, stochastic variability, use of AI
Jozef Magdolen      PhD student, signal analysis, periodic/quasiperiodic variability, use of AI
Sabína Vašová      identification of variable frequency using AI (ex-diploma thesis)
Andrej Dobrotka       scientific leader, astrophysicist (This email address is being protected from spambots. You need JavaScript enabled to view it.)

 

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Advanced Technologies Research Institute
Faculty of Materials Science and Technology in Trnava
Slovak University of Technology in Bratislava
Jána Bottu 8857/25
917 24 Trnava
GPS:  48.37088 17.572509

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