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We present the spectral and temporal radiative signatures expected within the “Supercritical Pile” model of Gamma Ray Bursts (GRBs). This model is motivated by the need for a process that provides the dissipation necessary in GRBs and presents a well defined scheme for converting the energy stored in the relativistic protons of the Relativistic Blast Waves (RBW) associated with GRB into radiation; at the same time it leads to spectra which exhibit a peak in the burst vFv distribution at an energy Ep ≃ 1 MeV in the observer’s frame, in agreement with observation and largely independent of the Lorentz factor Γ of the associated relativistic outflow. Futhermore, this scheme does not require acceleration of particles at the shock other than that provided by the isotropization of the flow bulk kinetic energy on the RBW frame. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Using the exact solution of the axisymmetric pulsar magnetosphere derived in a previous publication and the conservation laws of the associated MHD flow, we show that the Lorentz factor of the outflowing plasma increases linearly with distance from the light cylinder. Therefore, the ratio of the Poynting to particle energy flux, generically referred to as σ, decreases inversely proportional to distance, from a large value (typically ≳10[SUP4]) near the light cylinder to σ ≃ 1 at a transistion distance R[SUBtrans]. Beyond this distance the inertial effects of the outflowing plasma become important and the magnetic field geometry must deviate from the almost monopolar form it attains between R[SUBlc] and R[SUBtrans]. We anticipate that this is achieved by collimation of the poloidal field lines toward the rotation axis, ensuring that the magnetic field pressure in the equatorial region will fall-off faster than 1/R[SUP2] (R being the cylindrical radius). This leads both to a value σ = σ[SUBs] ≪ 1 at the nebular reverse shock at distance R[SUBs] (R[SUBs] ≫ R[SUBtrans]) and to a component of the flow perpendicular to the equatorial component, as required by observation. The presence of the strong shock at R = R[SUBs] allows for the efficient conversion of kinetic energy into radiation. We speculate that the Crab pulsar is unique in requiring σ[SUBs] ≃ 3 x 10[SUP-3] because of its small translational velocity, which allowed for the shock distance R[SUBs] to grow to values ≫ R[SUBtrans]. [ABSTRACT FROM AUTHOR]

We present the structure of the axisymmetric force-free magnetosphere of an aligned rotating magnetic dipole, in the case in which there exists a sufficiently large charge density (whose origin we do not question) to satisfy the ideal MHD condition: E · B = 0, everywhere. The unique distribution of electric current along the open magnetic field lines which is required for the solution to be continuous and smooth is obtained numerically. We expect that our solution will be useful as the starting point for detailed studies of pulsar magnetospheres under more general conditions, namely when either the force-free and/or the ideal MHD condition E · B = 0 are not valid in the entire magnetosphere. Based on our solution, we consider that the most likely positions of such an occurrence are the polar cap, the crossings of the zero space charge surface by open field lines, and the return current boundary, but not the light cylinder. [ABSTRACT FROM AUTHOR]