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GCN Circular 35043

GRB 231115A: archival HST observations
2023-11-15T20:01:14Z (6 months ago)
Andrew Levan at Radboud University <>
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A.J. Levan (Radboud), B. Gompertz (Birmingham), D.B. Malesani (DAWN/NBI) report:

The field of GRB 231115A (Mereghetti et al. GCN 35037) has been previously observed on several occasions by the Hubble Space Telescope via targeted observations of M82. Visual inspection of the location of the suggested candidate identified by Kumar et al. (GCN 35041) indicates that the environment is unremarkable. In blue observations obtained in F435W (GO 10776, 29-03-2006), the source lies on the stellar field of the host galaxy, but no readily identifiable discrete sources can be seen (e.g. massive stars or star-forming regions). In the IR, the field resolves into a larger number of discrete sources, likely due to the smaller extinction. Several sources are present within the 0.6” error region in F110W observations (GO 11360, 01-01-2010) with magnitudes around F110W=22 (AB). However, the density of such sources at this location in the galaxy is such that none is an outstanding candidate to be physically associated with the optical transient identified by Kumar et al.

We note that this location is relatively remote from the bulk of M82 and is not obviously associated with substantial star-forming activity. Although not unprecedented, this would be a somewhat unusual location for a magnetar giant flare.
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