Fast Radio Bursts by Stellar Wind Microlensing of a Faint Background Source

Abstract By assuming the inverse square law of solar wind plasma density as representative of other stars, it is shown that just outside a star, the outward deflection of a passing radio signal at ν ≈ 1 GHz (which is capable of penetrating the plasma) is about 5 times larger than the gravitational inward deflection by the star, and the ensuing lens equation, which takes both effects into account is a cubic polynomial with three roots and a new strong lensing caustic. The geometric optics approach is valid for a radio source size ≲1 pc. Microlensing magnification of a steady background source occurs typically over a timescale of milliseconds, resulting in ≈80 fast radio bursts (FRBs) per day over the whole sky, which can only perturb the isotropy of FRB distribution at the several percent level. Moreover, repeating FRBs could be triggered by the periodic interception of the line of sight of the background source by members of a binary system. The temporal signatures of such FRBs are consistent with the power spectrum of solar wind density fluctuations on corresponding scales, except that the mean density of the wind is a few times higher than the solar value.