GCN Circular 7688
Subject
GRB 080506: TLS afterglow detection in VRIZ
Event
Date
2008-05-07T04:02:27Z (18 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, C. Hoegner and S. Ertel (TLS Tautenburg) report:
We observed the afterglow of Swift GRB 080506 (Baumgartner et al., GCN
7685, Kawabata et al., GCN 7686) with the Tautenburg 1.34m Schmidt
telescope 0.32 days after the GRB in good conditions (moderate
transparency but excellent seeing). We obtained a total of six 600 sec
exposures, in the sequence Rc, V, Ic, Z, Z, Z before twilight forced us to
shut down. The afterglow is well (Rc, V, Ic) and faintly (Z) detected in
single images, and well detected in the 1800 sec stack of the three Z
images.
We find an afterglow position
R.A. (J2000) = 21:57:41.775
Dec. (J2000) = +38:59:05.86
in comparison with the USNOB1.0 catalog, with a precision of 0".5 in each
coordinate. This is fully in agreement with the UVOT (Baumgartner et al.,
GCN 7685) and enhanced XRT (Osborne et al., GCN 7687) positions.
Assuming the star at
R.A. (J2000) = 21:57:39.84
Dec. (J2000) = +38:58:28.25
to have Rc = 16.7 (magnitude is basically identical in R1 and R2
magnitudes), we find for the afterglow:
time Rc dRc
0.31576 20.77 0.13
Taking the two measurements from Kawabata et al. (GCN 7686), we find a
shallow decay slope of alpha = 0.6 between 0.0025 and 0.316 days after the
GRB.
Our (and Swift's) clear detection in the V band implies z <~ 4. On the
other hand, this was an image trigger, with faint emission seen up to ~
200 seconds. The initial XRT light curve (XRT repository, Evans et al.
2007) is flat until 200 seconds before dropping off very steeply. This may
suggest that this GRB lies at moderately high redshift (3 - 4).
Spectroscopy is encouraged.
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