GCN Circular 9253

Subject

GRB090424: R-band detection (37.5 hrs post-burst), jet break?

Event

Date

2009-04-26T11:30:29Z (17 years ago)

From

Myungshin Im at Seoul Nat U <mim@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 9223Loading...
 
 ) 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 9248Loading...
 
 ),
  more than the expected amount of fading with the power-law index
  of 0.71 reported earlier (Urata et al. GCN 9247Loading...
 
 ). 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.