Skip to main content
Testing. You are viewing the public testing version of GCN. For the production version, go to
New Announcement Feature, Code of Conduct, Circular Revisions. See news and announcements

GCN Circular 9458

GRB 090530: break in light curve
2009-05-31T12:36:48Z (15 years ago)
Jochen Greiner at MPI <>
A. Rossi (Tautenburg), F. Olivares, and J. Greiner (both MPE Garching)
report on behalf of the GROND team:

We observed the field of GRB 090530 (Swift trigger 353567, Cannizzo et al.,
GCN #9438) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m
MPI/ESO telescope at La Silla Observatory (Chile). Observations started on
31 May 2009 at 00:36 UT, 21.3 h after the burst.

We detect the optical/NIR afterglow (Cannizzo et al., GCN #9438;
Flewelling et al., GCN #9439; Morgan et al., GCN #9440; Nissinen & Hentunen,
GCN #9442) in stacked exposures of 20 min in JHK and 24 min in g'r'i'z'. 

Calibrating the r' band data against the USNO star at RA = 11:57:41.7, 
Dec = +26:35:43, we obtain R = (22.2 +-0.2) mag. Comparing this with 
the white light magnitudes obtained by ROTSE (Flewelling et al., GCN #9439),
UVOT (Schady et al., GCN #9450) and GRAS002 (Nissinen & Hentunen,
GCN #9442) as well as the NOT R-band magnitude (Malesani et al., GCN #9452),
we find a break in the optical light at around 22 ksec post-burst (i.e.
before the NOT observation), with slopes of 0.5+-0.1 (pre-break) and 
1.8+-0.4 (post-break).  We note that a break at this time is also visible
in the Swift/XRT data (see repository; Evans et al. 2007).
Looking for U.S. government information and services? Visit