A Photosphere-Internal Shock Model of Gamma-Ray Bursts: Case Studies of Fermi/LAT Bursts

Understand

Radially inhomogeneous gamma-ray burst (GRB) jets release variable photospheric emission and can have internal shocks occurring above the photosphere.

• We generically formulate a photospheric emission model of GRBs including Compton up-scattered photospheric (UP) emission off the electrons (and positrons) in the internal shocks, and find that the photospheric emission may correspond to the traditional (Band) component at <~1 MeV and the UP emission to the high-energy emission observed by Fermi/LAT for some GRBs at >~ 10 MeV.
• The two components can be separate in the spectrum in some cases or can mimic a smooth broad Band spectrum in other cases.
• We apply our formulation to the well-studied long and short LAT GRBs, GRB 080916C, GRB 090902B, and GRB 090510, and typically find reasonable parameters for fitting the time-binned spectra, although fine tuning of several parameters is required.