GCN Circular 11502
Subject
GRB 101225A: WHT observations
Event
Date
2010-12-27T19:18:03Z (15 years ago)
From
Klaas Wiersema at U of Leicester <kw113@star.le.ac.uk>
K. Wiersema, N. Tanvir (Leicester) and A. Levan (Warwick) report:
We observed the afterglow of GRB 101225A (Racusin et al. GCN 11493; Xu et al.
GCN 11496) with the 4.2m William Herschel Telescope.
We used the ACAM instrument to obtain imaging in r and i filters, and low
resolution spectroscopy.
The afterglow is clearly detected in individual images of 300 second
exposure, at R=22.8 +/- 0.2 mag (uncertainties are dominated by scatter in
USNO-B star magnitudes), at 28.2 hrs after burst. The source appears
pointlike, in the 1.1 arcsecond seeing conditions. We note that this
magnitude compared with the Xu et al value (GCN 11496) implies a very
shallow decay.
We obtained two low resolution spectra immediately following the imaging,
each with 1200 second exposure time. Continuum emission is detected
in the 5000 - 9300 A range, but no significant emission or absorption
lines are detected. Detection of continuum up to 5000 A gives a formal
constraint on the redshift of z<3.1.
At the redshift estimated by Campana et al. (GCN 11501) we would expect to
detect emission lines in the ACAM spectra (e.g. Balmer lines, [O III]),
implying that the spectrum is either strongly dominated by the afterglow
(the host is faint) or that the emission lines are redshifted into
wavelength areas dominated by strong skylines.
We thank Ovidiu Vaduvescu for excellent support.