arXiv subjects

A. A. Grokhovskaya

Publications and source records attributed to A. A. Grokhovskaya.

4 recordsLinked to original sources

arXiv2022

Mass estimation of the very massive galaxy cluster SRGe CL2305.2$-$2248 from strong lensing

The galaxy cluster SRGe CL2305.2$-$2248 (SPT-CL J2305$-$2248, ACT-CL J2305.1$-$2248) is one of the most massive clusters at high redshifts ($z \simeq 0.76$) and is of great interest for cosmology. For an optical identification of this cluster, deep images were obtained with the 1.5-m Russian-Turkish telescope RTT-150. Together with the open archival data of the Hubble Space Telescope, it became possible to identify candidates for gravitationally lensed images of distant blue galaxies in the form of arcs and arclets. The observed giant arc near the brightest cluster galaxies allowed us to estimate the radius of the Einstein ring, which is $ 9.8 \pm 1.3 $ arcseconds. The photometric redshift of the lensed source was obtained ($ z_s = 2.44 \pm 0.07 $). Its use in combination with the Einstein radius estimate made it possible to independently estimate the \cl2305 mass. It was done by extrapolating the strong lensing results to large radii and using the model density distribution profiles in relaxed clusters. This extrapolation leads to mass estimates $ \sim 1.5-3 $ times smaller than those obtained from X-ray and microwave observations. A probable cause for this discrepancy may be the process of cluster merging, which is also confirmed by SRGe CL2305.2-2248 morphology in the optical range.

astro-ph.CO↗

arXiv2021

First tidal disruption events discovered by SRG/eROSITA: X-ray/optical properties and X-ray luminosity function at z<0.6

We present the first sample of tidal disruption events (TDEs) discovered during the SRG all-sky survey. These 13 events were selected among X-ray transients detected in the 0<l<180 deg hemisphere by eROSITA during its second sky survey (10 June - 14 December 2020) and confirmed by optical follow-up observations. The most distant event occurred at z=0.581. One TDE continued to brighten at least 6 months. The X-ray spectra are consistent with nearly critical accretion onto black holes of a few 10^3 to 10^8 M_Sun, although supercritical accretion is possibly taking place. In two TDEs, a spectral hardening is observed 6 months after the discovery. Four TDEs showed an optical brightening apart from the X-ray outburst. The other 9 TDEs demonstrate no optical activity. All 13 TDEs are optically faint, with Lopt/Lx<0.3 (Lopt and Lx being the g-band and 0.2-6 keV luminosity, respectively). We have constructed a TDE X-ray luminosity function, which can be fit by a power law with a slope of -0.6+/-0.2, similar to the trend observed for optically selected TDEs. The total rate is estimated at (1.1+/-0.5)10^-5 TDEs per galaxy per year, an order of magnitude lower than inferred from optical studies. This suggests that X-ray bright events constitute a minority of TDEs, consistent with models predicting that X-rays can only be observed from directions close to the axis of a thick accretion disk formed from the stellar debris. Our TDE detection threshold can be lowered by a factor of ~2, which should allow a detection of ~700 TDEs by the end of the SRG survey.

astro-ph.HE↗

arXiv2021

Observation of a very massive galaxy cluster at z=0.76 in SRG/eROSITA all-sky survey

The results of multiwavelength observations of the very massive galaxy cluster SRGe CL2305.2-2248 detected in X-rays during the first SRG/eROSITA all-sky survey are discussed. This galaxy cluster was also detected earlier in microwave band through the observations of Sunyaev-Zeldovich effect in South Pole Telescope (SPT-CL J2305-2248), and in Atacama Cosmological Telescope (ACT-CL J2305.1-2248) surveys. Spectroscopic redshift measurement, $z=0.7573$, was measured at the Russian 6-m BTA telescope of SAO RAS, in good agreement with its photometric estimates, including a very accurate one obtained using machine learning methods. In addition, deep photometric measurements were made at the Russian-Turkish 1.5-m telescope (RTT150), which allows to study cluster galaxies red sequence and projected galaxies distribution. Joint analysis of the data from X-ray and microwave observations show that this cluster can be identified as a very massive and distant one using the measurements of its X-ray flux and integral comptonization parameter only. The mass of the cluster estimated according to the eROSITA data is $M_{500}=(9.0\pm2.6)\cdot10^{14}\, M_\odot$. We show that this cluster is found among of only several dozen of the most massive clusters in the observable Universe and among of only a few the most massive clusters of galaxies at $z>0.6$.

astro-ph.CO↗

arXiv2021

Measurement of the supermassive black hole masses in two active galactic nuclei by the photometric reverberation mapping method

We present the results of long-term photometric monitoring of two active galactic nuclei, 2MASX J08535955+7700543 (z $\sim$ 0.106) and VII Zw 244 (z $\sim$ 0.131), being investigated by the reverberation mapping method in medium-band filters. To estimate the size of the broad line region, we have analyzed the light curves with the JAVELIN code. The emission line widths have been measured using the spectroscopic data obtained at the 6-m BTA telescope of SAO RAS. We give our estimates of the supermassive black hole masses $\lg (M/M_{\odot})$, $7.398_{-0.171}^{+0.153}$, and $7.049_{-0.075}^{+0.068}$, respectively

astro-ph.GA↗