Observations and Theoretical Implications of GRB 970228

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Abstract
GRB 970228 is the first gamma-ray burst (GRB) for which prolonged postburst transient X-ray, optical, and infrared emission has been detected. Recent Hubble Space Telescope (HST) observations show that the transient consists of two components: a point source, which is known to be fading, and an extended source, which is possibly fading. I fit standard fireball remnant models to the first month of X-ray, optical, and infrared measurements, which may be done without assuming a GRB distance scale. I show that its emission is consistent with that of the remnant of a relativistically expanding impulsive fireball in which a forward shock dominates the emission of the GRB event: the piston model. However, two discrepant measurements may indicate that the postburst flux varies by a factor of ~3 on timescales of days or weeks. Furthermore, using the HST observations and the fitted model, I show that the extended object probably is fading, which may place GRB 970228 at Galactic halo distances.

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