[vsnet-grb-info 1939] GRB050805a : Null detection report

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3776
SUBJECT: GRB050805a : Null detection report
DATE:    05/08/06 12:33:27 GMT
FROM:    Eran Ofek at Tel Aviv U.  <eran at wise1.tau.ac.il>

E. O. Ofek, Y. Lipkin (Wise observatory, TAU) report:

We have observed the error box of the of the Swift trigger 149118
(Cummings et al. 2005, GCN 3766; designated as GRB 050805a by Lipunov et
al. GCN 3767), using the Wise observatory 1m telescope + Tek CCD camera,
starting at 2005, Aug 05th, 21:50 UTC.
Comparing a 300 sec R-band image which we obtained (mid exposure time
0.15851 days after the Swift-BAT trigger) to the POSS2 R-band image,
we did not detect any new source in the 2" error circle of the optical
transient that was reported by Lipunov et al. (GCN 3767).
The limiting magnitude of our image was R=19.5.

If we understood correctly the message of Lipunov et al., then
our observations took place 2.637 hrs after theirs.
If Lipunov et al. indeed detected the OT, and further
assuming a power-law decay, this time difference would imply a
decay-rate index that is larger than 2.08.

We note that according to GCN 3766, GRB050805a
is probably not a real GRB.