Speaker
Description
The tidal forces from SMBHs can disrupt stars in their vicinity. These tidal disruption events (TDEs) manifest themselves as a luminous, short-lived, flares coming from the nuclei of otherwise quiescent galaxies and represent an important tool to study the properties of dormant SMBHs. They are exquisite multi-wavelength sources, as they produce very bright flares in different bands of the electromagnetic spectrum, extending from X-rays to radio wavelengths, with the prompt emission usually peaking in the UV/optical and/or in soft X-rays.
The first TDE candidates were discovered in the X-rays band and thanks to the increasing survey power in the time domain astronomy the population of observed TDEs has quickly grown. Now they represent a class of optical nuclear transients with distinct observational features.
However, the origin of the diverse emission properties of TDEs are not fully understood. Three different scenarios have recently been proposed: outflows, emission by shocks from intersecting debris streams and thermal reprocessing of accretion power by a layer of gas. These models are still under discussion and imply different geometries of the emitting region and thus they predict different observing features. Dense multivawelength monitoring campaigns are fundamentals to investigate the underlying TDE emission mechanisms and the advent of Swift satellite represented a major step in the TDE monitoring strategies, finally allowing for systematic and early-started follow-up in the UV and X-rays bands, beside the usual optical monitoring. This resulted in revealing an intriguing and puzzling diversity in the observational properties of the TDE population.
I will present the results from a dense multi-wavelength photometric and spectroscopic follow-up campaign of the TDE AT2017gge. Thanks to a promptly started Swift follow-up, a soft X-ray flare delayed with respect to the optical/UV peak has been detected and it was found to be rapidly followed by a MIR echo and by the emergence of a number of long-lasting high ionization coronal emission lines. Remarkably, a transient high ionization coronal NIR line is also detected. These observations proved for the first time a clear connection between a TDE flare and the appearance of extreme coronal emission lines (ECLEs). The implication on the underlying UV/Optical emission mechanism and on the properties of the emitting region will be accurately discussed.
