1. Developing of a new, GR-R-MHD code- “cuHARM” (cuda-HARM). This code, use several algorithms that are optimized for run on GPU-based cluster, aimed at studying accretion and ejection in the vicinity of black hole (BH), including the effects of strong magnetic fields and radiation. For the radiative calculations, we solve the radiative transfer on a separate grid, which enable accurate trace of the photons as they propagate in the different direction without the use of moments. This is needed to study events that occur close to the photosphere, where photons decouple the plasma, and using moments of the radiative transfer equation can result in significant errors. Using this code, whose development had been only recently completed, we study the structure of accretion disks and the emerging jets under various conditions. So far, we quantified the amount of angular momentum deposited by the jet, and discovered a structural change in the disk when the accretion rate increases above a certain value, caused by radiative cooling. These results have been published so far in 3 papers and many more are currently being prepared; furthermore, they were presented in several international conferences and meetings.
2. We proposed a novel explanation to the “plateau” phase seen in ~60% of GRBs, as due to terminal Lorentz factor of tens, rather than 100’s. This result has the potential to lead to a paradigm shift in understanding these objects, as it affects both the properties of the progenitors, the jet composition and the ambient environment. We thus looked for supporting evidence, and recently found that analyzing late time flares, as well as the GRB prompt signal itself, may provide independent support to this claim. These works were published in several papers.
3. Another major breakthrough we had was the calculation of population inversion that occurs when relativistic particles interact with Alfven waves. This is a plausible scenario that can explain fast radio bursts (FRBs), in which strong coherent emission is observed. Population inversion is a necessary ingredient in synchrotron maser, one of the leading candidates of explaining this phenomenon. This is the first work that calculates the wave-particle interaction from basic physical principle, and finds that a significant fraction, of 10-20% of the energy is available for the masing process. Thereby, this work is the first to suggest a complete scenario that can explain FRBs. It was published in two papers so far, another one is currently being written.
4. The improvement of the radiative transfer algorithms enables us to study a novel phenomenon: photon energy gain by multiple scattering inside a relativistically expanding jet, that is characterized by a velocity shear (gradient). This mechanism is analogue to Fermi acceleration of charged particles, and is capable of reproducing an observed power law spectral index. Only that here no particles are accelerated, only photons are scattered back and forth. In a serious of papers, we investigated various consequences of this scenario, which include a natural way of explaining the observed spectral slopes during GRB prompt emission, as well as a natural explanation to the observed spectral lags. We further implemented this idea to the study of active galactic nuclei (AGNs), and showed that this model can be at work in these objects as well.
5. We studied the basic physics of shock waves. In particular, we were focused on (1) the transition between the collisional and collisionless regimes; and (2) on the ability of shock waves to accelerate particles to high energies= cosmic rays. We found that there is an upper limit on the fraction of particles that can be accelerated to high energy, which does not exceed 30%.
