[vsnet-grb-info 14175] GRB 130925A: HST imaging

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15489
SUBJECT: GRB 130925A: HST imaging
DATE:    13/11/16 09:22:23 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3 at star.le.ac.uk>

N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick), R. Hounsell,
A. S. Fruchter (STScI), S. B. Cenko (NASA/GSFC), D. A. Perley (Caltech),
P. T. O'Brien (U. Leicester) report:

We imaged the location of GRB 130925A (Evans et al. GCN 15251;
Sudilovsky et al. GCN 15247) with HST at two epochs, at 20 days and
47 days post-burst respectively, in the F814W (I-band), F110W (J-band)
and F160W (H-band) filters.

The host galaxy is well resolved and appears to be an almost edge-on spiral.
The galaxy shows signs of disturbance: specifically the disk shows asymmetry
and the bulge appears to be extended perpendicular to the disk, suggestive
of a polar-ring morphology.

Image subtraction reveals evidence of faint transient light in the first epoch
in all three filters.  The location is in good agreement with that from prior 
ground-based imaging of the GRB.  The transient position is close to the disk 
plane, which likely accounts for the high extinction and X-ray column for this 
event (Evans et al. GCN 15254).  It is, however, slightly offset from the 
nucleus of the galaxy by about 0.12 arcsec (~600pc in projection).  This 
would initially seem to be in conflict with a possible tidal disruption origin 
for this event, although if the galaxy morphology is indicative of a recent 
major merger, then it is plausible that the system currently contains more 
than one super-massive black hole.

Further analysis is ongoing.

We thank the staff at STScI for approving and expediting
these ToO observations.