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Afterglow of the Gamma Ray


The above image shows the field of the Gamma Ray Burst GRB 011121 as observed with the 6.5m Baade telescope and "Classic Cam" infrared imager on UT 2001 Nov 29.3. The exposure time was 4320 seconds in the Js passband with 0.5" seeing in the combined image.

A source at the position of the GRB afterglow is marginally detected, but because of its faintness, it is difficult to separate a possible point source from the underlying fuzz. Differential PSF-fitting photometry relative to the bright stars in the field yields J = 21.9 +/- 0.1 for the source at the position of the GRB afterglow. Because of the marginal detection, this should be viewed as an upper limit.


Two other sources are detected near the GRB position. One bright source is located 0.8"S and 2.0"E of the GRB with J = 19.98 +/- 0.04. This object may be the core of the GRB host galaxy, but it is not clearly resolved -- it might be a foreground star. The other source (the "blob") located 1.6"S and 2.6" E of the GRB is clearly detected at J = 21.57 +/- 0.07, and is possibly extended.


This image shows a composite of the Baade Telescope Js image of the GRB with a Js image obtained on a Nov 22.4 with the du Pont 2.5m telescope at Las Companas. The total integration in the du Pont image was only 90 seconds, but the afterglow is strongly detected at the 10-sigma level. The magnitude of the transient on this date was estimated as J ~ 16 mag. Adopting the decay slope reported from optical observations would predict J ~ 21 for the afterglow at the time of the Baade Telescope image.
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