[vsnet-grb-info 20562] GRB 180418A: NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22660
SUBJECT: GRB 180418A: NOT optical observations
DATE:    18/04/19 00:20:53 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

Daniele Malesani (DAWN/NBI and DARK/NBI), Kasper Elm Heintz (Univ. 
Iceland and DAWN/NBI), Maria Stone (Univ. Turku), and James Stone, 
report on behalf of a larger collaboration:

We observed the optical afterglow (Zheng & Filippenko, GCN 22647; 
Guidorzi et al., GCN 22648; Troja et al., GCN 22652; Fong et al., GCN 
22659) of GRB 180418A (D'Elia et al., GCN 22646) with the 2.5-m Nordic 
Optical Telescope (NOT) equipped with StanCam.

Observations were carried out in the Bessel R filter, but calibrated 
against SDSS r-band Pan-STARRS local photometry. A low S/N source is 
detected at a position consistent with previous reports.

At a mid time of April 18.936 UT (15.72 hr after the trigger), we 
measure for the counterpart r = 22.70 +- 0.15 AB.

Compared to the Gemini-North measurement (Fong et al., GCN 22659), we 
infer a decay slope alpha = 0.75 +- 0.17, assuming F(t) propto t^-alpha.