Talk detail

Participant	Giannios, Dimitrios
Institution	Purdue University - 525 Northwestern Avenue - Purdue - West Lafayette, IN - USA

Session	GRB1	Accepted	No	Order		Time
Talk	Oral abstract	Title	Photospheric emission in magnetic outflow models in GRBs
Co-authors
Abstract

Session	GRB1	Accepted	Yes	Order	2	Time	14:30 - 14:55
Talk	Oral abstract	Title	Photospheric emission in the magnetic outflow models in GRBs
Co-authors
Abstract	The radiation released at the transparency radius of an ultrarelativistic flow can account for the observed properties of gamma-ray bursts (GRBs) provided that sufficient energy is dissipated in the sub-photospheric region. In this talk, I will outline how the magnetic reconnection model for GRB jets predicts the required energy release below and above the photosphere to reproduce the observed Band spectrum. In the second part of the talk, I generalize my treatment of photospheric emission. I show how the peak energy of the Ef(E) spectrum and its overall shape depend on the properties of the jet in a generic model. I find that continuous energy release which results in electron heating over a wide range of distances may well be the key to explain the GRB emission. In this picture, the peak of the spectrum forms at a Thomson optical depth of several tens. The peak depends mainly on the bulk Lorentz factor Γ of the flow and can, therefore, be used to determine it. The Γ is predicted to range from ~10 to 1000 from X-ray flashes to the brightest observed GRBs in agreement with recent observational inferences. The Amati relation can be understood if the brightest bursts are the least baryon loaded ones. Implications from this interpretation of the GRB emission for the central engine are discussed.