TITLE:   GCN CIRCULAR
NUMBER:  9220
SUBJECT: GRB 090423 limiting magnitudes
DATE:    09/04/24 11:36:15 GMT
FROM:    Arne A. Henden at AAVSO  <arne@aavso.org>

A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3),
D. Terrell (SwRI), and W. Cooney (SRO) report:

We observed the field of GRB 090423 (Krimm et al., GCN 9198)
using the 35cm telescope of Sonoita Research Observatory
with an automated VOevent trigger for an R-band image
sequence.  Images began at 07:58:09UT on 2009-04-23,
170 seconds after the burst, under good conditions.

The afterglow candidate reported by Tanvir et al. (GCN 9202),
Levan et al. (GCN 9206), Cucchiara et al. (GCN 9209),
and shown by Olivares et al. (GCN 9215) to have both faded
and to have a photo-z of 8.0, is not detected in our images.
We place 3-sigma constraints of

200 seconds midpoint (1min image)  Rc < 18
350 seconds midpoint (6min stack)  Rc < 20

using USNO-A red magnitudes.  The 19 total images, covering
the period 07:58:09 through 08:47:34, can be obtained from
ftp://ftp.aavso.org/public/sro/grb090423/