TITLE:   GCN CIRCULAR
NUMBER:  21635
SUBJECT: LIGO/Virgo G298048: observations of optical counterpart candidate with CHILESCOPE observatory
DATE:    17/08/21 16:11:53 GMT
FROM:    Alexei Pozanenko at IKI,Moscow  <grbgw.iki@gmail.com>

A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), 
M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration:

We observed  the possible counterpart SSS17a/DLT17ck (Coulter et al. 
GCN 21529;  Yang et al., GCN 21531) of LIGO/Virgo trigger G298048 (LVC 
GCNs 21509, 21513)  with RC-1000 telescope of CHILESCOPE observatory. 
The observations carried out in clear filter in two epochs, on Aug. 19 
and Aug.20.

Photometry of the transient SSS17a/DLT17ck is following

Date       UT start  Filter    OT   Err UpLim (3 sigma)


2017-08-19 23:30:33   CR       16.7 0.2 21.9
2017-08-20 23:21:09   CR       18.5 0.2 22.0

The photometry is based on several nearby USNO-B1.0 stars (R2). The 
photometry  is still preliminary and required  careful estimation of 
NGC4339 influence. Nevertheless it is evident the source is fading 
significantly which is confirmed by many observations (e.g. Im et al., 
GCN 21632 and references in the GCN 21632).

We are grateful for the team of remote controlled CHILESCOPE observatory 
(www.chilescope.com) for observations.