Wide-field time-domain surveys across the multi-wavelength spectrum have revealed a complex array of transient and variable phenomena from SMBH populations, including flares from tidal disruption events (TDEs), ‘changing-look’ events when AGN broad lines appear or disappear following an optical flare, and other classes of extreme AGN variability. These events provide important insights into...
Almost all galaxies contain a supermassive black hole (masses > 100,000 solar masses) residing at their center. In the last decade or so a subsample of these black holes are found to exhibit repeating X-ray modulations with timescales ranging from a few minutes to up to a month. The nature of these recurring signals is currently debated but most ideas can be put into two categories: they are...
Galactic nuclei are extreme environments where stars are densely packed around a supermassive black hole (SMBH). Occasionally, dynamical interactions in the galactic center cause stars to interact violently at short distances with each other or with the SMBH, resulting in the formation of nuclear transients. In this talk, I will discuss two types of extreme nuclear transients: extreme tidal...
Extragalactic Fast X-ray Transients (FXTs) are X-ray flashes lasting minutes to hours. Their nature is unclear, but the most remarkable scenarios related to them are shock breakout supernovae, tidal disruption events involving white dwarf stars and intermediate massive black holes, and binary neutron star mergers. Observing them using different wavelength facilities in the coming hours and...
The four completed SRG Observatory half-year all-sky surveys have yielded a significant number of variable X-ray sources.
The SRG/eROSITA telescope has discovered a rich population of tidal disruption events (TDE) that exhibit strong X-ray variability.
Searching for TDE in the X-ray band offers certain advantages over a selection in the optical range.
In X-rays, the background flux of the...
The Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a mission conceptdeveloped by a large European collaboration under study by ESA since2018 and currently one of the three candidate M7 mission for a launch in mid '30s. THESEUS aims at fully exploiting Gamma-Ray Bursts for investigating the early Universe and as keyphenomena for multi-messenger astrophysics. By providing an...
The Iranian National Observatory (INO) is poised to become a significant contributor to the global effort in monitoring and following up on transient astronomical events. With its 3.4-meter optical telescope strategically located in a low-density region of telescopes on Mount Gargash at 3600 m above sea level in central Iran, the INO offers a unique opportunity to fill critical gaps in the...
