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○ 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 on to black holes of a few × 103 to 108 M⊙, 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 Lg/LX < 0.3 (Lg 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.

No abstract

Context. We present observations from the short-term intensive optical campaign (from September 2019 to January 2020) of the changing-look Seyfert NGC 3516. This active galactic nucleus is known to have strong optical variability and has changed its type in the past. It has been in the low-activity state in the optical since 2013, with some rebrightening from the end of 2015 to the beginning of 2016, after which it remained dormant. Aims. We aim to study the photometric and spectral variability of NGC 3516 from the new observations in U-and B-bands and examine the profiles of the optical broad emission lines in order to demonstrate that this object may be entering a new state of activity. Methods. NGC 3516 has been monitored intensively for the past 4 months with an automated telescope in U and B filters, enabling accurate photometry of 0.01 precision. Spectral observations were triggered when an increase in brightness was spotted. We support our analysis of past-episodes of violent variability with the UV and X-ray long-term light curves constructed from the archival Swift/UVOT and Swift/XRT data.Results. An increase of the photometric magnitude is seen in both U and B filters to a maximum amplitude of 0.25 mag and 0.11 mag, respectively. During the flare, we observe stronger forbidden high-ionization iron lines ([Fe vii] and [Fe x]) than reported before, as well as the complex broad Hα and Hβ lines. This is especially seen in Hα, which appears to be double-peaked. It seems that a very broad component of ∼10,000 km s −1 in width in the Balmer lines is appearing. The trends in the optical, UV, and X-ray light curves are similar, with the amplitudes of variability being significantly larger in the case of UV and X-ray bands. Conclusions. The increase of the continuum emission, the variability of the coronal lines, and the very broad component in the Balmer lines may indicate that the AGN of NGC 3516 is finally leaving the low-activity state in which it has been for the last ∼3 years.

We report the discovery of a nearby massive white dwarf with He-H atmosphere. The white dwarf is located at a distance of 74.5 ± 0.9 pc. Its radius, mass, effective temperature, H/He ratio and age are R = 2500 ± 100 km, M = 1.33 ± 0.01 $\rm M_{\odot }$, Teff = 31200 ± 1200 K, H/He ∼ 0.1 and 330 ± 40 Myr, respectively. The observed spectrum is redshifted by Vr = +240 ± 15 km s−1, which is mostly attributed to the gravitational redshift. The white dwarf shows a regular stable photometric variability with amplitude Δg ≈ 0.06m and period P = 353.456 s suggesting rapid rotation. This massive, hot and rapidly rotating white dwarf is likely to originate from the merging of close binary white dwarf system that avoided explosion in a thermonuclear type Ia supernova.

Results of U BV RIJHKLM photometry and V RI polarimetry of a young star RW Aur A observed during unprecedented long and deep (up to ∆V ≈ 5 mag) dimming events in 2010-11 and 2014-18 are presented. The polarization degree p of RW Aur A at this period has reached 30 per cent in the I band. As in the case of UX Ori type stars (UXORs), the so-called 'bluing effect' in the colour-magnitude V versus V − R c , V − I c diagrams of the star and a strong anticorrelation between p and brightness were observed. But the duration and the amplitude of the eclipses as well as the value and orientation of polarization vector in our case differ significantly from that of UXORs. We concluded that the dimmings of RW Aur A occurred due to eclipses of the star and inner regions of its disc by the axisymmetric dust structure located above the disc and created by the disc wind. Taking into account both scattering and absorption of stellar light by the circumstellar dust, we explain some features of the light curve and the polarization degree -magnitude dependence. We found that near the period of minimal brightness mass-loss rate of the dusty wind was > 10 −9 M ⊙ yr −1 .