TITLE:   GCN CIRCULAR
NUMBER:  15956
SUBJECT: GRB 140311A: Nanshan afterglow decay
DATE:    14/03/12 00:51:27 GMT
FROM:    Dong Xu at DARK/NBI  <dong.dark@gmail.com>

D. Xu (DARK/NBI), C.-H. Bai, X. Zhang, A. Esamdin, L. Ma (XAO) report:

The previously reported afterglow candidate (Xu et al., GCN 15947) has
been decaying throughout our R-band observations. Part of the
photometry are listed below

Tmid (hr)   Mag(R)  MagErr(R)
2.06778     21.06      0.10
1.53056     20.80      0.10
0.49306     19.96      0.10

All magnitude are calibrated with the following three SDSS stars using
Lupton (2005) transformation:
SDSS J135709.54+003731.9   m(r)=16.81, m(i)=16.30
SDSS J135716.45+003657.3   m(r)=16.41, m(i)=16.10
SDSS J135713.38+003942.0   m(r)=18.57, m(i)=18.47

Together with measurements in Klotz et al. (GCN 15952) and D'Avanzo et
al. (GCN 15953), it shows that the optical afterglow peaks at ~0.23 hr
post-burst and is decaying roughly as F(t) ~ t^-0.75 since ~0.5 hr
post-burst.