TITLE:   GCN CIRCULAR
NUMBER:  22867
SUBJECT: GRB 180624A: NOT optical counterpart
DATE:    18/06/27 19:06:20 GMT
FROM:    Jonatan Selsing at DARK/NBI  <jselsing@dark-cosmology.dk>

Jonatan Selsing (DAWN/NBI), Kasper E. Heintz (Univ. Iceland and DAWN/NBI), Johan P. U.
Fynbo (DAWN/NBI), Daniele B. Malesani (DAWN/NBI and DARK/NBI), Jyri J. Lehtinen
(MPS), Teemu Willamo (Univ. of Helsinki), report on behalf of a larger
collaboration:

We observed the optical afterglow (Guidorzi, GCN #22839; Schady, GCN #22840;
Rossi et al., GCN #22845; Watson et al., GCN #22846; Guidorzi et al., GCN
#22858) of GRB 180624A (Gibson et al., GCN #22832) with the 2.5-m Nordic Optical
Telescope (NOT) equipped with StanCam.

Observations were carried out in the Bessel R filter, but calibrated against
Pan-STARRS r-band local photometry, using the transformations of Lupton (2005).
An optical afterglow is detected at a position consistent with previous reports.

At a mid time 11.0 hr after the BAT trigger, we measure for the counterpart R =
20.10 +- 0.04 (Vega). This measurement has not been corrected for Milky Way
extinction (A_V = 0.13). Due to the vicinity of the nearby galaxy noted by
Schady (GCN #22840), Guidorzi et al. (GCN #22858), and Rossi et al. (GCN 22845),
we cannot exclude some minor contamination from this object to the afterglow
photometry.