A. N. Semena

Estimation of plasma parameters in an accretion column near the surface of accreting white dwarfs from their flux variability

We consider the behavior of matter in the accretion column that emerges under accretion in binary systems near the surface of a white dwarf. The plasma heated in a standing shock wave near the white dwarf surface efficiently radiates in the X-ray energy band. We suggest a method for estimating post-shock plasma parameters, such as the density, temperature, and height of the hot zone, from the power spectrum of its X-ray luminosity variability. The method is based on the fact that the flux variability amplitude for the hot region at various Fourier frequencies depends significantly on its cooling time, which is determined by the parameters of the hot zone in the accretion column. This allows the density and temperature of the hot matter to be estimated. We show that the characteristic cooling time can be efficiently determined from the break frequency in the power spectrum of the X-ray flux variability for accreting white dwarfs. The currently available X-ray instruments do not allow such measurements to be made because of an insufficient collecting area, but this will most likely become possible with new-generation large-area X-ray spectrometers.

On the area of accretion curtains from fast aperiodic time variability of the intermediate polar EX Hya

We present results of a study of the fast timing variability of the magnetic cataclysmic variable (mCV) EX Hya. It was previously shown that one may expect the rapid flux variability of mCVs to be smeared out at timescales shorter than the cooling time of hot plasma in the post shock region of the accretion curtain near the WD surface. Estimates of the cooling time and the mass accretion rate, thus provide us with a tool to measure the density of the post-shock plasma and the cross-sectional area of the accretion funnel at the WD surface. We have probed the high frequencies in the aperiodic noise of one of the brightest mCV EX Hya with the help of optical telescopes, namely SALT and the SAAO 1.9m telescope. We place upper limits on the plasma cooling timescale

Additional spectroscopic redshift measurements for galaxy clusters from the first Planck catalogue

\tau<

On-ground calibration of the ART-XC/SRG mirror system and detector unit at IKI. Part I

0.3 sec, on the fractional area of the accretion curtain footprint

Sample of cataclysmic variables detected in the 400d X-ray survey

f<1.6\times10^{-4}

Constraints on accretion column parameters for the intermediate polar LS Pegasi from the power spectrum of its optical light curve

, and a lower limit on the specific mass accretion rate

Low-Frequency Quasi-Periodic Oscillations in the X-ray Nova MAXI J1535-571 at the Initial Stage of Its 2017 Outburst

\dot{M}/A \gtrsim

Aperiodic X-ray flux variability of EX Hya and the area of the base of the accretion column at the white dwarf surface

3 g/sec/cm

On-ground calibration of the ART-XC/SRG instrument

^{-2}

Studying temporal variability of GRS 1739–278 during the 2014 outburst

. We show that measurements of accretion column footprints via eclipse mapping highly overestimate their areas. We deduce a value of