2001/05/31 by B. Scott Gaudi, Jonathan Granot, Abraham Loeb
Physics and Astronomy · #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/323244
14 pages, including 3 figures and 1 Table, very minor changes. Accepted to ApJ main journal. To appear in the November 1, 2001 issue (v561)
arxiv created 2001/07/02 · openalex publication_date 2001/11/01 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/04
The optical afterglow of gamma-ray burst (GRB) 000301C exhibited a significant, short timescale deviation from the power-law flux decline expected in the standard synchrotron shock model. Garnavich, Loeb, & Stanek found that this deviation was well fitted by an ad hoc model in which a thin ring of emission is microlensed by an intervening star. We revisit the microlensing interpretation of this variability, first by testing whether microlensing of afterglow images with realistic surface brightness profiles (SBPs) can fit the data, and second by directly inverting the observed light curve to obtain a nonparametric measurement of the SBP. We find that microlensing of realistic SBPs can reproduce the observed deviation, provided that the optical emission arises from frequencies above the cooling break. Conversely, if the variability is indeed caused by microlensing, the SBP must be significantly limb-brightened. Specifically, ≥60% of the flux must originate from the outer 25% of the area of the afterglow image. The latter requirement is satisfied by the best-fit theoretical SBP. The underlying optical/infrared afterglow light curve is consistent with a model in which a jet is propagating into a uniform medium with the cooling break frequency below the optical band.