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We report on the SRG /eROSITA detection of ultra-soft (⁠|$kT=47^{+5}_{-5}$|  eV) X-ray emission (L X = |$2.5^{+0.6}_{-0.5} \times 10^{43}$|  erg s−1) from the tidal disruption event (TDE) candidate AT 2022dsb ∼14 d before peak optical brightness. As the optical luminosity increases after the eROSITA detection, then the 0.2–2 keV observed flux decays, decreasing by a factor of ∼39 over the 19 d after the initial X-ray detection. Multi-epoch optical spectroscopic follow-up observations reveal transient broad Balmer emission lines and a broad He  ii 4686 Å emission complex with respect to the pre-outburst spectrum. Despite the early drop in the observed X-ray flux, the He  ii 4686  Å complex is still detected for ∼40 d after the optical peak, suggesting the persistence of an obscured hard ionizing source in the system. Three outflow signatures are also detected at early times: (i) blueshifted H α emission lines in a pre-peak optical spectrum, (ii) transient radio emission, and (iii) blueshifted Ly α absorption lines. The joint evolution of this early-time X-ray emission, the He  ii 4686 Å complex, and these outflow signatures suggests that the X-ray emitting disc (formed promptly in this TDE) is still present after optical peak, but may have been enshrouded by optically thick debris, leading to the X-ray faintness in the months after the disruption. If the observed early-time properties in this TDE are not unique to this system, then other TDEs may also be X-ray bright at early times and become X-ray faint upon being veiled by debris launched shortly after the onset of circularization. [ABSTRACT FROM AUTHOR]

We present an extensive radio monitoring campaign of the nuclear transient eRASSt J234402.9−352640 with the Australia Telescope Compact Array, one of the most X-ray luminous TDE candidates discovered by the SRG/eROSITA all-sky survey. The observations reveal a radio flare lasting >1000 d, coincident with the X-ray, UV, optical, and infrared flare of this transient event. Through modelling of the 10 epochs of radio spectral observations obtained, we find that the radio emission is well-described by an expanding synchrotron emitting region, consisting of a single ejection of material launched coincident with the optical flare. We conclude that the radio flare properties of eRASSt J234402.9−352640 are consistent with the population of radio-emitting outflows launched by non-relativistic tidal disruption events, and that the flare is likely due to an outflow launched by a tidal disruption event (but could also be a due to a new AGN accretion event) in a previously turned-off AGN. [ABSTRACT FROM AUTHOR]

The ROSAT -selected tidal disruption event (TDE) candidate RX J133157.6−324319.7 (J1331) was detected in 1993 as a bright [0.2–2 keV flux of (1.0 ± 0.1) × 10−12 erg s−1 cm−2], ultra-soft (kT  = 0.11 ± 0.03 keV) X-ray flare from a quiescent galaxy (z  = 0.051 89). During its fifth all-sky survey (eRASS5) in 2022, Spectrum-Roentgen-Gamma (SRG)/ eROSITA detected the repeated flaring of J1331, where it had rebrightened to an observed 0.2–2 keV flux of (6.0 ± 0.7) × 10−13 erg s−1 cm−2, with spectral properties (kT  = 0.115 ± 0.007 keV) consistent with the ROSAT -observed flare ∼30 yr earlier. In this work, we report on X-ray, ultraviolet, optical, and radio observations of this system. During a pointed XMM observation ∼17 d after the eRASS5 detection, J1331 was not detected in the 0.2–2 keV band, constraining the 0.2–2 keV flux to have decayed by a factor of ≳40 over this period. Given the extremely low probability (∼5 × 10−6) of observing two independent full TDEs from the same galaxy over a 30 yr period, we consider the variability seen in J1331 to be likely caused by two partial TDEs involving a star on an elliptical orbit around a black hole. J1331-like flares show faster rise and decay time-scales [ |$\mathcal {O}(\mathrm{d})$| ] compared to standard TDE candidates, with negligible ongoing accretion at late times post-disruption between outbursts. [ABSTRACT FROM AUTHOR]

White dwarf black hole tidal disruption events (herein WTDEs) present an opportunity to probe the quiescent intermediate mass black hole population in the Universe. We run an extensive set of Monte Carlo based simulations to explore SRG/eROSITA's detection sensitivity to WTDEs as a function of black hole mass, redshift, and time offset between event flaring and it first being observed. A novel estimate of WTDE rate densities from globular clusters and dwarf galaxies is also presented. We combine this with estimated detection sensitivities to infer the rate of eROSITA detecting these events. Depending on the estimate of the intrinsic rate of WTDEs, we anticipate that eROSITA may detect three events over its 4 yr all-sky survey. eROSITA will be most sensitive to systems with black hole masses above |$10^4\, \mathrm{M}_{\odot }$|⁠ , and is most likely to catch these within 5 d of flaring. [ABSTRACT FROM AUTHOR]

We explore a new Bayesian method of detecting galaxies from radio interferometric data of the faint sky. Working in the Fourier domain, we fit a single, parameterized galaxy model to simulated visibility data of star-forming galaxies. The resulting multimodal posterior distribution is then sampled using a multimodal nested sampling algorithm such as multinest. For each galaxy, we construct parameter estimates for the position, flux, scale length, and ellipticities from the posterior samples. We first test our approach on simulated SKA1-MID visibility data of up to 100 galaxies in the field of view (FOV), considering a typical weak lensing survey regime (SNR ≥ 10) where 98 per cent of the input galaxies are detected with no spurious source detections. We then explore the low-SNR regime, finding our approach reliable in galaxy detection and providing in particular high accuracy in positional estimates down to SNR ∼ 5. The presented method does not require transformation of visibilities to the image domain, and requires no prior knowledge of the number of galaxies in the FOV, thus could become a useful tool for constructing accurate radio galaxy catalogues in the future. [ABSTRACT FROM AUTHOR]