TITLE:   GCN CIRCULAR
NUMBER:  22162
SUBJECT: GRB 171123A: Tautenburg observations
DATE:    17/11/24 16:01:55 GMT
FROM:    Sylvio Klose at TLS Tautenburg  <klose@tls-tautenburg.de>

S. Schmidl, B. Stecklum, S. Klose, A. Nicuesa Guelbenzu, and C. Hoegner 
(Thueringer Landessternwarte Tautenburg) report:


We observed the field of GRB 171123A (Evans et al., GCN 22148) in the Rc 
band using the Tautenburg Schmidt telescope equipped with the prime focus 
CCD camera. Observations started at 04:01 UT, about 14 hr after the burst.

At the SE border of the enhanced XRT error circle (radius 1.9 arcsec; Goad 
et al., GCN 22150; 1.5 arcsec acc. to the newest results presented at
http://www.swift.ac.uk/xrt_positions/00791922/) we find a faint source at 
coordinates

RA (J2000) : 12:24:59.29,
Dec (J2000): 32:30:03.4  (+/- 0.6 arcsec).

At a midtime of 04:46 UT we measure a preliminary magnitude of Rc (Vega) = 
22.7 +/- 0.3, calibrated against SDSS field stars.

The non-detection of this source by RATIR eight hours after our observing 
run (Butler et al., GCN 22160) suggests that this was the GRB afterglow. 
We caution however that this is only a 3-sigma detection.