[vsnet-grb-info 7699] GRB090424: R-band detection (37.5 hrs post-burst), jet break?

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9253
SUBJECT: GRB090424: R-band detection (37.5 hrs post-burst), jet break?
DATE:    09/04/26 11:30:29 GMT
FROM:    Myungshin Im at Seoul Nat U  <mim at astro.snu.ac.kr>

  M. Im, W. Park, Y. Jeon, I. Lee (CEOU/Seoul National Univ),
  Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team.

   We continued the follow-up observation of GRB090424 (Cannizzo et al.
  GCN 9223) in BVR using the 1.0m telescope at Mt. Lemmon (Arizona, US)
  operated by the Korea Astronomy Space Science Institute.
   The R-band imaging started at 2009 April 26, 03:11:23 UT.
   The mid-point of the R-band obseravation is April 26,
  03:39:43 UT (37.45 hrs after the burst).

   From a stacked image of 13 frames (3 min exp. each),
  the afterglow is visible at R=20.96 +- 0.17 mag, suggesting
  a significant fading occurred since last night (Im et al. GCN 9248),
  more than the expected amount of fading with the power-law index
  of 0.71 reported earlier (Urata et al. GCN 9247). This suggests that
  jet break might have occured. The afterglow is also visible in
  B- and V-bands.
   The photometry was calibrated against USNO-B1 stars in the vicinity.

   We thank the LOAO operator, J. Yoon for his assistance for this
  observation.