The pulse widths, dispersion measures and dispersion indices of Fast Radio Bursts (FRB) impose coupled constraints that all models must satisfy. Conventional single thin screen scattering models imply electron densities were >~20/cm^3, 10^8 times the mean intergalactic density. This problem is resolved if the radiation scattered close to its source, where high densities are plausible. Observation of dispersion indices close to their low density limit of -2 sets a model-independent upper bound on the electron density and a lower bound on the size of the dispersive plasma cloud, excluding terrestrial or Solar System origin. The scattering and much of the dispersion may be attributed to regions about 1 AU from the sources, with electron densities ~ 3E8/cm^3. The inferred parameters are only marginally consistent; re-examination of the assumed relation between dispersion measure and distance is warranted. Origin in an ionized starburst or protogalaxy is suggested, but statistical arguments exclude cosmologically local compact young SNR.

Host: Saul Rappaport

Note:  refreshments at 3:45pm, talk begins at 4:00pm

Image credit:  Observers’ Data, Thornton, et al. (2013)