D. Xu (DARK/NBI), H.-B. Niu, X. Zhang, A. Esamdin, L. Ma (XAO) report:
We observed the LAT field of GRB 131231A (Sonbas et al., GCN 15640)
using the 1m telescope located on Mt. Nanshan, Xinjiang, China,
equipped with a 1.2x1.2 deg^2 CCD camera. We obtained a series of 120s
and 300s frames at the mean time 12:40 UT on 2013-12-31 (i.e., 7.91 hr
after the Fermi trigger).
Within the LAT error circle (RA, Dec 10.585, -1.845 with an error
radius of 0.149 deg, error statistical only) reported in Sonbas et al.
(GCN 15640), no new prominent uncatalogued source is found and the
depth of the Nanshan image is similar to that of DSS II. Given that
the above LAT error is statistical only, we thus inspect that
surrounding region the LAT error circle and discovered a bright
source, not present in both DSS II and SDSS, at coordinates
Err Radius: ~1.5 arcsec
with a magnitude of R~17.6, calibrated with nearby USNO B1 stars.
Follow-up observations are encouraged to check whether the source is
the afterglow of the burst.