[vsnet-grb-info 18632] GRB 161017A: LT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20080
SUBJECT: GRB 161017A: LT optical observations
DATE:    16/10/19 08:29:40 GMT
FROM:    Cristiano Guidorzi at Ferrara U,Italy  <guidorzi at fe.infn.it>

C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), C.G. Mundell 
(U. Bath), A. Gomboc (U. Nova Gorica), N.R. Tanvir (U. Leicester) on 
behalf of a large collaboration report:

The 2-m Liverpool Telescope observed Swift GRB161017A (Troja et al., GCN 
20064) in the SDSS r and i filters on October 19, from 03:45 to 05:37 UT 
(mid time~1.45 days since the GRB). We clearly detect the optical 
afterglow (Yurkov et al. GCN 20063; Troja et al. GCN 20064; de 
Ugarte-Postigo et al. GCN 20069; Fujiwara et al GCN 20070; Melandri et 
al. GCN 20071) with the following values, as calibrated against nearby 
SDSS stars:

Mid Time      Exposure       Filter       Magnitude
(days)           (s)
-------------------------------------------------------
1.42            5x120         SDSS-R      20.02 +- 0.03
1.42            5x120         SDSS-I      19.80 +- 0.03
-------------------------------------------------------

Compared with our previous report (Guidorzi et al. GCN 20072), we 
estimate an average power-law decay index alpha~1.3 between 0.68 and 
1.45 days post burst.