GCN Circular 9063
Subject
GRB 090323: Further TLS detections - a break?
Date
2009-04-01T02:22:46Z (15 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, U. Laux, F. Ludwig and B. Stecklum (TLS Tautenburg) report:
We observed the afterglow (Updike et al., GCN 9026, Cenko et al. GCN 9027)
of the intense Fermi GBM/LAT GRB 090323 (Ohno et al., GCN 9021) with the
1.34m Schmidt telescope of the TLS Tautenburg observatory at several
epochs.
At ~6 days after the GRB, conditions were bad (low transparency and
passing clouds). We obtained 21 Rc frames of 600 seconds exposure time
each. Only four of these are usable. The afterglow is faintly detected in
the complete stack.
Using the same comparison star as Kann et al. (GCN 9033), we measure the
following afterglow magnitude:
days after trigger Exposure Rc dRc (statistical)
5.89127 4 x 600 23.13 0.50
At ~7 days after the GRB, conditions were very bad (almost complete
overcast). We obtained 1 Rc frames of 600 seconds exposure time which had
good quality. The afterglow is not detected.
days after trigger Exposure Rc
6.99881 1 x 600 > 22.50
This limit is not constraining.
At ~9 days after the GRB, conditions were very good (good transparency,
good seeing, but influence of moonlight). We obtained 12 Rc frames of 600
seconds exposure time each. The afterglow is faintly detected in the
complete stack.
days after trigger Exposure Rc dRc (statistical)
8.90324 12 x 600 23.64 0.36
Compared to the flattening of the decay noted by de Ugarte Postigo et al.
(GCN 9051) and already hinted at in earlier TLS and Lick data (Kann et
al., GCN 9041, Perley, GCN 9042), the decay has steepened again, an
indication of a (jet?) break. On the other hand, the last TLS detection
agrees well with the extrapolation of the earlier decay (Kann et al., GCN
9041), indicating that the plateau may be a rebrightening/optical flare
spanning a few days.
Due to increasing moonlight, no further TLS observations are planned.
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