TITLE:   GCN CIRCULAR
NUMBER:  17693
SUBJECT: GRB 150413A: Nanshan optical and radio follow-ups
DATE:    15/04/13 16:14:57 GMT
FROM:    Dong Xu at NAOC/CAS  <dong.dark@gmail.com>

D. Xu (NAOC), X. Zhang, C.-H. Bai, G.-J. Feng, A. Esamdin, L. Ma,
J.-Z. Liu (XAO), Y. Qin (Geneva Observatory), J.-P. Yuan, Z.-G. Wen
(XAO) report:

We observed the field of GRB 150413A (Markwardt et al., GCN 17688;
Serino et al., GCN 17691) using the 1m telescope located at Nanshan,
Xinjiang, China. Observations started at 15:00:38 UT on 2015-04-13,
i.e., 1.09 hr after the burst and a series of 150s R-band images were
obtained and observations are ongoing.

The OT reported by MASTER (Ivanov et al., GCN 17689; Tyurina et al.,
GCN 17690) is within the BAT error circle, and it is clearly detected
in each of our images. Preliminary reduction shows that the OT has
been decaying very slowly since our observations. It has m(R) ~ 15.4
at 1.115 hr post-burst and has m(R) ~ 15.8 at 1.724 hr post-burst,
calibrated with the same USNO B1 star (#1618-0098185, R=15.59, close
to R1=16.02). The OT's lightcurve behavior is unusual compared to
normal GRB optical afterglows, although it indeed could be the
afterglow of the GRB.

We note that there is a bright and much extended galaxy within the BAT
error circle. However, we didn't find any apparent new point source
within the galaxy, compared to DSS.

In addition, we observed the field using the Nanshan 25m radio dish in
the pulsar searching mode, to check if there is any radio pulse mimicking a fast
radio burst and following the BAT trigger.

[GCN OPS NOTE(21apr15):  Per author's request, the mode in the last sentence
was changed from "timing mode" to "pulsar searching mode".]