TITLE:   GCN CIRCULAR
NUMBER:  16748
SUBJECT: GRB 140818B: TLS observations
DATE:    14/08/27 09:23:17 GMT
FROM:    Sebastian Schmidl at TLS Tautenburg  <schmidl@tls-tautenburg.de>

S. Schmidl, S. Klose, D. A. Kann, U. Laux, L. Pfeifer, C. Pohl, and H.
Meusinger (all TLS Tautenburg) report:

We observed the field of GRB 140818B (Swift trigger 609885, Vargas et al.,
GCN 16709) with the 1.34m Tautenburg Schmidt telescope.

Starting at 20:34 UT (1.83 hr after the trigger), we obtained in total 12
x 120s Rc-band images. Observations were obtained at a mean airmass of 1.75.

In a stack of all available images, we detect the source reported by
Aceituno et al. (GCN 16711). Using USNO-B1 field stars for calibration, we
derive a preliminary magnitude (Vega magnitude system) of

Rc = 20.9 +/- 0.2,

at a midtime of 2.08 hr after the burst.

The given magnitude is not corrected for the large Galactic foreground
extinction corresponding to a reddening of E_(B-V) = 0.73 mag in the
direction of the burst (Schlegel et al. 1998).