Lecturer: Dr. Gill Ramandeep Affiliation: Open University of Israel Abstract: The magnetization and composition of relativistic outflows that give rise to gamma- ray bursts (GRBs) remain open questions. Studies thus far have largely focused on baryon dominated (weakly magnetized) jets that produce non-thermal gamma-rays at internal shocks by synchrotron and inverse Compton emission. However, there are many problems with this model and it's becoming more and more clear that GRB jets should have high magnetization. Poynting flux dominated jet models make use of magnetic reconnection and/or turbulence as a mechanism to dissipate energy gradually and continuously in the flow. This is an important feature as it helps in regulating the temperature of electrons in both Thomson thick and thin flows. In this talk, I will describe the evolution of strongly magnetized, baryon depleted, photon-rich outflows both pre- and post-jet- breakout from the confining Wolf-Rayet stellar envelope. I will highlight the importance of distributed heating in the jet by hydromagnetic turbulence, a critical ingredient, which helps in the formation of the GRB spectrum. I will argue that the soft spectral component must form in the Thomson thick part of the flow (pre-jet- breakout), and the high energy emission must be delayed until the flow has become optically thin and highly relativistic (post- jet-breakout). Finally, I will show how a thin baryonic layer lifted from the confining medium actively drives dissipation in the flow to generate the high energy spectral tails. Additional details of the upcoming Astrophysics' seminars can be found on the following link. ‏האירוע הזה כולל שיחת וידאו ב-Google Hangouts. הצטרף: https://hangouts.google.com/hangouts/_/mail.huji.ac.il/astrophysics?hceid=bWFpbC5odWppLmFjLmlsX2c0czhydDlpcmhwZzRvdGNybWIzZGFqcjdvQGdyb3VwLmNhbGVuZGFyLmdvb2dsZS5jb20.82jibttvgsmu1ahsidjfi9dov4&hs=121