Astrolunch: Jonathan Katz (WUSTL)

Wed, 03/06/2020 - 16:00 to 17:00

Title: The SGR–FRB connection
The discovery that the Galactic SGR 1935+2154 emitted FRB 200428 simultaneous with a gamma-ray flare demonstrated the association of these phenomena. If FRB radio emission is the result of coherent curvature radiation, the net charge of the coherent charge ``bunches'' or waves may be estimated. A statistical argument indicates that the radiating charge bunches must have a Lorentz factor >25. The observed radiation frequencies indicate that the phase velocity (pattern speed) of the radiating bunches corresponds to a Lorentz factor >100. Coulomb repulsion implies that the electrons making up these bunches have yet larger Lorentz factors. Acceleration of these more energetic electrons must overcome their incoherent curvature radiation, which limits their Lorentz factors. These electrons also Compton scatter in the soft gamma-ray field of the SGR. In FRB 200428 the power radiated coherently at radio frequencies exceeded that of Compton scattering, but in more luminous SGR outbursts Compton scattering dominates, precluding the acceleration of energetic electrons, explaining the absence of a FRB associated with the giant 27 December 2004 outburst of SGR 1806-20. SGR with luminosity >10^{42} ergs/s do not emit FRB, while those of lesser luminosity may do so.