TITLE:   GCN CIRCULAR
NUMBER:  18179
SUBJECT: GRB 150818A: Continued NOT monitoring - afterglow confirmation
DATE:    15/08/20 10:59:44 GMT
FROM:    Steve Schulze at U of Iceland  <sts30@hi.is>

S. Schulze (PUC, MAS), J. P. U. Fynbo, D. Malesani (DARK/NBI), R. Tuma, S. Dinh, M. Homann, M. Munoz (NBI) and P. Jakobsson (U. Iceland) report on behalf a larger collaboration:

We observed the field of GRB 150818A (D'Elia et al., GCN 18152) with the Nordic Optical Telescope (NOT) equipped with ALFOSC. We obtained a 300-s image in R band. Observations started at 21:03 UT on August 19 (i.e. 1.39 days after the burst).

We clearly detect the source reported in Marshall et al. (GCN 18155), McCauley et al. (GCN 18161), Schulze et al. (GCN 18164) and Mazaeva et al. (GCN 18175). We measure R=21.18 +/- 0.05 calibrated against several USNO stars. The optical transient faded by 0.3 mag compared to Schulze et al. (GCN 18164) in agreement with Mazaeva et al. (GCN 18175) who also found evidence for a shallow decay. Sanchez-Ramirez (GCN 18177) hinted that the host is possibly detected in GTC image. A significant host contribution would explain the shallow decay.

[GCN OPS NOTE(20aug15):  Per author's request, the 18177 id_num for the S-R reference was added.]