Gamma-ray Burst 090520

(All information courtesy of the instrument teams.)

Previous IAU Circulars

• none

• GCN Circular #9417
  J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team):
  On May 20, 2009 at 01:37:16 UT, BAT triggered on GRB 090520 (trigger #352671). The burst was weak, and the instrument failed to find a source in onboard analysis. A significant source was found in ground analysis. The source is located at RA, Dec 11.613, -8.000 deg, which is

     RA(J2000)  =  00h 46m 27.1s
     Dec(J2000) = -08d 00' 00"
  

  with an uncertainty of 3 arcmin (radius, sys+stat, 90%=20 containment). The partial coding was 48%.
  The burst consisted of a single FRED pulse, starting about T-2 seconds, with a T90 of 20 =B1 5 seconds (estimated error=20 including systematics).
  The BAT event data for failed triggers is limited to 10 seconds. =20 Using 10 seconds of event data from T-2 to T+8 seconds, the best fit to the spectrum is a simple powerlaw with a photon index of 0.8 +- 0.2. The fluence for this interval in the 15-150 keV band was 3.4 =B1 0.5 x 10-7 ergs/cm2=20 (68% confidence).
  The BAT source position was about 3 arcmin from a low-redshift galaxy, 6dFGS gJ004613.4-080000. This is an emission-line=20 galaxy at z =3D 0.0850.
  A Swift TOO was requested, but initially the source was in the Swift Moon constraint. In any case was 52 degrees (~2.5 hours=20 in RA) from the Sun, not in constraint, but still an unfavorable=20 angle, so no Swift followup observation is planned.
• GCN Circular #9420
  A. Rossi (Tautenburg), T. Kruehler and J. Greiner (both MPE Garching) report on behalf of the GROND team:
  GROND (Greiner et al. 2008, PASP 120, 405) at the 2.2m ESO/MPI telescope at La Silla Observatory (Chile) started follow-up observations of GRB 090520 (Cummings et al. 2009, GCN #9417) on May 21, at 09:35 UTC (~32 h after the burst). In addition, a second epoch of imaging was obtained, which started on May 22, 09:37 UTC.
  Image subtraction does not reveal any variable source between the two epochs. The first epoch thus yields the following upper limits:

  g > 23.8
  r > 24.0
  i > 23.4
  z > 23.2
  J > 21.8
  H > 21.4
  K > 20.8
  

  obtained using the GROND zeropoints and 2MASS field stars as reference.