TITLE:   GCN CIRCULAR
NUMBER:  21387
SUBJECT: GRB 170728B iTelescope observation
DATE:    17/07/29 23:19:08 GMT
FROM:    Takanori Sakamoto at AGU  <tsakamoto@phys.aoyama.ac.jp>

Y. Kitaoka, T. Sakamoto (AGU)

We observed the field of GRB 170728B detected by Swift (Cenko et al., GCN Circ. 21371)
with the iTelescope.Net (http://www.itelescope.net) T16 (Takahashi TOA-150) telescope
located at the AstroCamp Observatory (Nerpio, Spain).  20 images of 60 sec exposures
were taken in the R filter starting from July 28  23:03:19 (UT) about  36 mimute after
the trigger and stopped on July 29 00:17:48 (UT).  We do not detect the optical afterglow
both in the individual images and the stacked image at the X-ray afterglow position.
The estimated five sigma upper limit of the combined image (total exposure of 1200 sec)
is ~15.8 using the USNO-B1 catalog.