TITLE:   GCN CIRCULAR
NUMBER:  11208
SUBJECT: GRB 100901A: UKIRT zYJHK Observation
DATE:    10/09/04 14:41:16 GMT
FROM:    Myungshin Im at Seoul Nat U  <mim@astro.snu.ac.kr>

  Myungshin Im, Changsu Choi, Hyunsung Jun, Eugene Kang (CEOU/Seoul
  National University), Y. Urata (NCU), P. Choi (Pomona College),
  T. Sakamoto (NASA/GSFC), N. R. Tanvir (U. Leicester), and A. Levan
  (U. Warwick) on behalf of a larger collaboration

   We observed GRB 100901A (Immler et al. GCN 11159) in z, Y, J, H,
  and K filters using UKIRT. The observation started at Sept. 04,
  10:49:31 UT or roughly 2.88 days after the BAT alert.
   We detect the afterglow in images in all the filters,
  with a preliminary magnitude of K=17.82 +- 0.2 mag (Vega)
  calibrated against a 2MASS star at RA=01h49m05.59s and Dec=22d44m51.86s.
   The K-band magnitude is consistent with an expected brightness
  in NIR assuming fading of the brightness with alpha=1.2 a spectral
  slope of beta=0.6 since the report of Kann et al. (GCN 11187).
   Further observation of the object is ongoing.