GCN Circular 6505
Subject
GRB 070610: TLS RRM sees flaring behaviour - Galactic transient?
Event
Date
2007-06-11T20:41:38Z (19 years ago)
From
Alexander Kann at TLS Tautenburg <kann@tls-tautenburg.de>
D. A. Kann, A. C. Wilson, S. Schulze, S. Klose, M. Henze, F. Ludwig, U.
Laux (TLS Tautenburg) and J. Greiner (MPE Garching) report:
We observed the XRT position (Pagani & Kennea, GCN 6490) of Swift GRB
070610 (Pagani et al. GCN 6489) with the Tautenburg 1.34m Schmidt
Telescope in Rapid Response Mode (Klose et al., GCN 3609). Observations
started 640 seconds after the trigger, at an initial airmass of 1.945.
Weather conditions were good and the airmass decreased during
observations. We obtained two sequences of images with 120 seconds
exposure time each, consisting of 6 Ic, 3 Rc and 3 V images per sequence.
The optical transient first detected by Stefanescu et al. (GCN 6492) and
confirmed by de Ugarte Postigo et al. (GCN 6501) is detected in only three
images, thus showing a rapid, short-lived flaring behaviour. Stacks of
images were created, but we do not detect the transient in these stacks.
We report the following upper limits and magnitudes assuming the USNO B1.0
star at RA = 19:55:03.2, Dec. = +26:14:14.5 has R2 = 15.8 and I = 15.32:
tmid (days) filter Exp. Limit OT mag
0.008407 Ic 1x120 19.7
0.012122 Ic 6x120 20.2
0.022194 Rc 3x120 21.2
0.033376 Ic 2x120 20.4
0.036369 Ic 1x120 20.2 19.36 +\- 0.15
0.040228 Ic 3x120 20.5
0.044356 Rc 1x120 21.3
0.046336 Rc 1x120 21.3 20.89 +\- 0.20
0.048304 Rc 1x120 21.3 21.78 +\- 0.50
The final detection is marginal.
We note that this flaring behaviour is very uncommon for the afterglow of
a GRB. Furthermore, the maps of Schlegel et al. 1998 give E(B-V) = 3.256,
tranlating to A_R = 8.7 and A_I = 6.3, at the position of the transient.
This would imply the flare in the I band reached 13th magnitude, very
unusual at such a late time. Furthermore, the X-ray afterglow as seen on
the Swift XRT repository webpage
(http://www.swift.ac.uk/xrt_curves/00281993/index.php) shows a more or
less constant behaviour, with small flares superposed.
The behaviour of the transient in both the optical and the X-ray regime as
well as the location in the Galactic plane strongly suggest that this is a
new Galactic transient source and not a GRB and its associated afterglow.
This message may be cited.
[GCN OPS NOTE(12jun07): Per author's request, "A_V" was changed to "A_I".]