Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...197.7305g&link_type=abstract
American Astronomical Society, 197th AAS Meeting, #73.05; Bulletin of the American Astronomical Society, Vol. 32, p.1519
Astronomy and Astrophysics
Astronomy
Scientific paper
The afterglow of the Gamma-Ray Burst (GRB) 000301C exhibited achromatic, short time-scale variability that is difficult to reconcile with the standard relativistic shock model. We interpret the observed light curves as a microlensing event superimposed on power-law flux decays typical of afterglows. In general, a relativistic GRB shock appears on the sky as a thin ring expanding at a superluminal speed. Initially the ring is small relative to its angular separation from the lens and so its flux is magnified by a constant factor. As the ring grows and sweeps across the lens its magnification reaches a maximum. Subsequently, the flux gradually recovers its unlensed value. This behavior involves only three free parameters in its simplest formulation and was predicted theoretically by Loeb & Perna (1998). Fitting the available R-band photometric data of GRB 000301C to a simple model of the microlensing event and a broken power-law for the afterglow, we find reasonable values for all the parameters and a reduced χ2/DOF parameter of 1.12 compared with 2.79 for the broken power-law fit alone. The peak magnification of ~ 2 occurred 3.8;days after the burst. The entire optical-IR data imply a width of the GRB ring of order 10% of its radius, similar to theoretical expectations. The angular resolution provided by microlensing is better than a micro-arcsecond. We infer a mass of approximately 0.5;Msun for a lens located half way to the source at z s=2.04. A galaxy 2'' from GRB 000301C might be the host of the stellar lens, but current data provides only an upper-limit on its surface brightness at the GRB position. This work was supported by NASA grants NAG5-9364 (PG), NAG5-7039 (AL) and HF-01124.01 (KS).
Garnavich Peter M.
Loeb Abraham
Stanek Kris Z.
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