ABSTRACT The Changing‐Look active galactic nucleus Mkn 590 is currently in a rejuvenated state, exhibiting a contemporaneous flux rise across X‐rays, UV, optical and cm wavelengths. In this study, we present three new optical spectra obtained with the Nordic Optical Telescope, alongside three 1.4 GHz continuum measurements from the Giant Meterwave Radio Telescope, acquired since Nov. 2024. We identified a clear increase in the broad hydrogen Balmer line emission in the most recent observational epochs. Additionally, the core radio flux densities appear to track the overall X‐ray variability, suggesting a possible connection between the accretion flow and jet activity. Based on these data, we aim to explore the evolution of the circumnuclear gas in this source and potential links between accretion and ejection activity.

ABSTRACT A series of extreme‐variability phenomena associated with supermassive black holes (SMBHs) in galactic nuclei are being revealed with increasing frequency in recent years thanks to enhanced survey capabilities across the electromagnetic spectrum. The observation of these extreme phenomena has opened the way to the study of the physics of SMBHs in real time—something that, until a decade ago, was exclusively associated with stellar‐mass black holes. A conference to discuss the physical processes powering these objects was held at ESAC, Madrid, Spain in June 2025.

ABSTRACT We present the results from a 3‐year‐long ultraviolet (UV) monitoring campaign of the broadline Seyfert 1 galaxy ESO 141–G55 using the International Ultraviolet Explorer (IUE). By modelling all individual, extinction‐corrected UV spectra in the 1150–1978 and 1850–3348 Å wavelength range, we have observed a significant variability in both UV continuum and line fluxes. Variabilities due to ionised UV lines like Si iv , Civ and He ii are delayed with respect to the UV continuum by , and days, respectively. At a distance of ∼0.004 c , an outer accretion disk can be a possible site for the origin of UV lines.

ABSTRACT The tidal field of a black hole can turn a star into a gas stream whose orbit can precess, especially if the a black hole is rapidly spinning. In this work, we investigate the impact of precession on the light curves of tidal disruption events (TDE). To do so, we perform two‐dimensional radiation‐hydrodynamic simulations of the interaction of the TDE wind and luminosity with the precessed stream wrapped around the black hole. Our results show that in events with black holes of and no orbit‐spin inclination, the line of sight has little effect on the light curves, since the stream covers a small fraction of the solid angle as the precession is confined to the orbital plane. In the case of black holes of and high inclination (), the light curve peaks can be delayed by ∼100 days due to presence of the precessed stream blocking the radiation in the early phase of the event. We also discuss our efforts to model self‐consistently the hydrodynamic evolution of a tidal stellar stream on curved spacetimes by the presence of a massive black hole.

ABSTRACT The Southern Galactic Disk Survey (GDS) monitored a mosaic of 268 fields along a ‐wide stripe in the southern Galactic disk with simultaneous observations in and () from September 2010 to September 2019. The survey design and data characteristics, as well as first results in , were presented by Haas et al. (2012; Paper I). Hackstein et al. (2015; Paper II) extended the photometry and analysis process, and introduced the first catalogue including photometry of all 268 fields in and light curves comprising up to 272 observations per field made between September 2010 and May 2015. Here we describe our custom‐made observational scheduler and conclude the GDS with light curves of up to 407 observations per field until September 2019 and light curves for a fraction of the fields. 113,449 distinct sources are identified as variables. Together with Paper II, we identified 77,592 variables that are not listed in either the International Variable Star Index (VSX) or the cross‐match catalogue by Gavras et al. (2023). All emerging catalogues, comprising light curves, photometry and reduced images, are made publicly available via the German Astrophysical Virtual Observatory (GAVO).

ABSTRACT Extragalactic nuclear transients that exhibit repeating outbursts can be modeled as the repeated dynamical interaction between bound stars and supermassive black holes (SMBHs). A subset of these transients, with recurrence timescales of months‐to‐years, have been explained as accretion flares from the repeated tidal stripping of a star by an SMBH, in a repeating partial tidal disruption event (rpTDE). We outline the scope of the rpTDE model and discuss hydrodynamical simulations and analytical predictions for the stability of stars undergoing repeated mass loss, and the long‐term evolution of these flares as a function of stellar type and orbital parameters. Our findings demonstrate that high‐mass and centrally concentrated stars undergo negligible changes in structure in response to small amounts () of mass loss, and can survive many mass‐stripping encounters with an SMBH. Contrarily, low‐mass and less evolved stars are unstable to mass loss, and would be destroyed within a few orbits. We discuss the implications of these results for constraining the stellar type and orbital parameters of observed sources, such as ASASSN‐14ko, for which flares have been observed, and AT2020vdq, which exhibits a second flare that is brighter than its primary outburst.

ABSTRACT TIC 277539431, a fast rotating M7 dwarf, was detected to host the highest latitude flare to date at . Magnetic activity like stellar flares occurring at high latitude indicate occurrence of coronal loops at these latitudes on fully‐convective M dwarfs. In contrast, sunspots usually occur below . In our study we look for modulation on the X‐ray signal occurring due to occultation of coronal loops by the star due to stellar rotation. We report an updated rotation period for this star as min based on TESS sectors 12, 37, 39, 64 and 65. We conducted fits by varying the amplitude and the phase of a sinusoidally modulated signal derived from the new rotation period. We find no evidence of rotational modulation in the X‐ray signal. This could be due to multiple scenarios, such as lack of a stable coronal loop during observation or the modulated signal being too weak, however given the dataset, individual scenarios cannot be distinguished.

ABSTRACT The cosmological Mass Varying Neutrino (MaVaN) model is considered, where the interaction between a fermionic field and a scalar field with a Ratra–Peebles potential via a Yukawa coupling is investigated. Observational constraints on the flat and non‐flat MaVaN models, as well as on the standard model, are derived from 32 measurements using MCMC analysis. Comparison with the model using the criteria , , and shows no statistically significant improvement for MaVaN models. Deviations in the expansion history remain well below , indicating that the data alone do not provide sufficient constraining power to distinguish MaVaN models from the model. The non‐flat MaVaN model reduces the tension between the value inferred from data and Planck CMB measurement from in the framework to . The discrepancy with the SH0ES measurement of is also reduced to below , primarily due to the large uncertainties of the data.