The work performed is divided to four work packages, each one dealing with a different phenomena. However there are strong links between the different parts.
With the discovery of gravitational waves from a binary neutron star merger in August 2017 we clearly focused on the first packages that deals with the electromagnetic counterpart that will accompany this phenomena. In fact already before August 2017 we have predicted some of the features that were observed. Once the event was detected we participated in some of the most important observations (in particular optical and radio observation) and in their interpretations and we have outline the basic picture of how the event looked. We have also worked on the interpretation of the observations to the question of whether or not neutron star mergers are the sites of production of heavy elements, the so called r-process elements, such as Gold, Uranium Plutonium and so on.
Tidal disruption events (TDEs), in which a star that wanders into the vicinity of a super massive black hole is torn apart by the black hole pose an interesting enigma. The standard model, accepted for thirty years or so predicts a luminosity that is much larger than what is observed. We consider this as an "inverse energy crisis'' and we have proposed an innovative solution to this puzzle, called elliptical or eccentric accretion (in which we have an elliptical accretion disk instead of the regular circular accretion models). After suggesting this model we have begun exploring its properties, first using linearized stability analysis and then using detailed numerical simulations. Additionally, at times super massive black hole are at the core of active galactic nuclei (AGN). These black hole operate as powerhouses that are powered by accretion. If a star is disrupted star within such a system its debris will encounter the disk producing a very different observational phenomena. Somewhat surprisingly it was never explored how a TDE will look like in such a case. We have explored for the first time a tidal disruption event that takes place around an AGN.
In a third part of the project we explored gamma-ray bursts (GRBs) these are the brightest cosmic explosions involving ultra relativistic jets that produce very high energy radiation. We have explored the physical conditions within the emission regions of GRBs and in particular we have shown that recent observations of sub-TeV radiation from GRB 190114C reveal the detailed conditions within the emission regions of GRBs and support our "pair balance" accretion model that we proposed in our earlier ERC grant. A significant part of this part involved exploration of the cocoon that arises when the jet propagates. The observations of the electromagnetic counterpart of the neutron star merger, mentioned earlier, revealed that cocoon emission was important also there, demonstrating nicely the interconnection between the seemingly unrelated different parts of this project. This part of the research culminated in early 2021 when a new window was opened towards GRBs with the discovery of TeV emission from GRB 202119c. We were the first to interpret the implications of this emission. Later on our detailed analysis demonstrated that these observations are fully consistent with the predictions of the predictions of our "detailed balance" model for particle acceleration in collisionless shocks.
