{
  "bibcode": "2010GCN.11502....1W",
  "body": "K. Wiersema, N. Tanvir (Leicester) and A. Levan (Warwick) report:\n\nWe observed the afterglow of GRB 101225A (Racusin et al. GCN 11493; Xu et al. \nGCN 11496) with the 4.2m William Herschel Telescope.\nWe used the ACAM instrument to obtain imaging in r and i filters, and low \nresolution spectroscopy.\n\nThe afterglow is clearly detected in individual images of 300 second \nexposure, at R=22.8 +/- 0.2 mag (uncertainties are dominated by scatter in \nUSNO-B star magnitudes), at 28.2 hrs after burst. The source appears \npointlike, in the 1.1 arcsecond seeing conditions. We note that this \nmagnitude compared with the Xu et al value (GCN 11496) implies a very \nshallow decay.\n\nWe obtained two low resolution spectra immediately following the imaging, \neach with 1200 second exposure time. Continuum emission is detected \nin the 5000 - 9300 A range, but no significant emission or absorption \nlines are detected. Detection of continuum up to 5000 A gives a formal \nconstraint on the redshift of z<3.1.\n\nAt the redshift estimated by Campana et al. (GCN 11501) we would expect to \ndetect emission lines in the ACAM spectra (e.g. Balmer lines, [O III]), \nimplying that the spectrum is either strongly dominated by the afterglow \n(the host is faint) or that the emission lines are redshifted into \nwavelength areas dominated by strong skylines.\n\nWe thank Ovidiu Vaduvescu for excellent support.",
  "circularId": 11502,
  "createdOn": 1293477483000,
  "email": "kw113@star.le.ac.uk",
  "subject": "GRB 101225A: WHT observations",
  "submitter": "Klaas Wiersema at U of Leicester  <kw113@star.le.ac.uk>",
  "eventId": "GRB 101225A"
}