TITLE: GCN CIRCULAR NUMBER: 8564 SUBJECT: GRB 081126: Confirmation of the Optical Afterglow DATE: 08/11/27 15:56:19 GMT FROM: Stephen Holland at USRA/NASA/GSFC/SSC S. T. Holland (CRESST/GSFC/USRA), P. A. Evans (U Leicester), F. E. Marshall (NASA/GSFC), P. Schady (MSSL), and R. Margutti (U Bicocca & OAB) report on the behalf of the Swift UVOT team: We confirm the optical afterglow of GRB 081126 reported by Sergeev & Pozanenko (2008, GCN Circ. 8558). A re-examination of the UVOT data shows that there is a fading source at RA (J2000) 21:34:03.59 = 323.51496 (deg) Dec (J2000) +48:42:38.3 = +48.71064 (deg) with an estimated uncertainty of 0.5 arcsec (radius, 90% confidence, statistical + systematic). This is consistent with the XRT error circle. Preliminary photometry and 3-sigma upper limits for this source are Filter T_start T_stop Exp(s) Mag Err ------------------------------------------------ white 75 225 147 18.82 0.09 u 289 420 127 18.17 0.13 v 5161 5361 197 19.29 0.32 b 4546 4746 197 20.20 0.28 u 5778 5976 197 >20.4 uvw1 5572 5771 197 >20.0 uvm2 5366 5566 197 >19.6 uvw2 4957 5156 197 >20.0 white 4751 4951 197 20.33 0.21 ------------------------------------------------ The quoted upper limits have not been corrected for the expected Galactic extinction along the line of sight corresponding to a reddening of E_{B-V} = 0.78 mag (Schlegel, et al., 1998, ApJS, 500, 525). All photometry is on the UVOT photometric system described in Poole et al. (2008, MNRAS, 383, 627). The detection in the u filter, combined with the lack of detections in the UV filters, is consistent with the afterglow having a redshift of approximately 2.4 < z < 3.8. However, this result is uncertain due to the large Galactic reddening along the line of sight to this source. The source identified in Holland & Margutti 2008, (GCN Circ. 8559) as being possibly extended is consistent with the catalogued position of the 2MASS point source 21340333+4842361. The separation between this 2MASS source and the afterglow is 3.2 arcsec. Since the photometry of the 2MASS source and the afterglow are consistent with both sources having at the same redshift it is possible that the 2MASS source is the host galaxy. Further observations are encouraged to confirm or reject this hypothesis. Holland & Margutti 2008, (GCN Circ. 8559) misidentified the optical afterglow as as the 2MASS point source 21340333+4842361. We apologize for any confusion caused by the misidentification in the previous UVOT Circular on GRB 081126.