On the External Shock Synchrotron Model for Gamma-ray Bursts' GeV Emission

摘要: The dominant component of the GeV gamma-ray burst emission detected by Large Area Telescope begins after prompt soft (sub-MeV) gamma rays and lasts longer. This has led to intriguing suggestion that is generated via synchrotron external shock. Moreover, limits on MeV afterglow lead at least in bright bursts field not amplified beyond compression We show here considerations confinement (within decelerating shock), efficiency, cooling emitting electrons constrain, within this model, magnetic fields arise both upstream (unshocked circumburst) downstream (shocked regions, allowing us put direct their values. well-known limit maximal emission, when combined with blast wave evolution, implies late photons (arriving more than ~100 s burst) energies higher ~10 do naturally from an shock almost certainly have a different origin. Finally, even modest seed flux (a few mJy) IR-optical would quench, Inverse Compton cooling, unless significantly behind An observation simultaneous will rule out model.