[AAVSO-HEN] GRB 090518 - NOT upper limit

[grb at aavso.org]

The following is a GCN Circular circulated via the AAVSO network.
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TITLE:   GCN CIRCULAR
NUMBER:  9423
SUBJECT: GRB 090518 - NOT upper limit
DATE:    09/05/26 07:21:31 GMT
FROM:    Johan U. Fynbo at U.Copenhagen  <jfynbo at astro.ku.dk>

C. C. Thoene (INAF/OAB), E. Kankare (NOT), J. P. U. Fynbo, D. Malesani
(DARK/NBI), A. J. Levan (Univ. Warwick), P. Jakobsson (Univ. Iceland),
J. Hjorth (DARK/NBI) report:

We observed the field of GRB 090518 (GCN 9386, Evans et al.) with
ALFOSC/NOT on La Palma starting May 18, 20:54 UT (21 h after the burst).
Observations were obtained in R (3x300s), I (3x300s) and z (6x200s)
filters at high airmass.

We do not detect any new source at the XRT position (GCN 9387, Evans et
al.) in the summed image of each filter. The following upper limits were
obtained (based on USNO B1.0 reference stars and a NOT z-band archival
zeropoint):

R > 23.7 mag
I > 21.8 mag
z(AB) > 22.5 mag