[vsnet-grb-info 20455] GRB 180325A: further NOT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22551
SUBJECT: GRB 180325A: further NOT observations
DATE:    18/03/26 23:43:36 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

Daniele Malesani (DAWN/NBI and DARK/NBI) and Johan P.U. Fynbo (DAWN/NBI) report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 180325A (Troja et al., GCN 22532) using the Nordic Optical Telescope (NOT) equipped with the AlFOSC imaging camera. The seeing in our observations was not good, around 2". 4 and 2 exposures by 600 s were obtained in the R and I filters, respectively.

The afterglow was not detected in R, and marginally (if at all) in I. The following magnitudes were computed with respect to nearby Pan-STARRS reference stars, and are therefore in the AB system.

Time (UT)    Time since GRB (hr) Filter  Magnitude
-----------------------------------------------------
Mar 25.856   18.65                r       >22.6
Mar 25.871   18.92                i       22.9 +- 0.3

These values are significantly fainter than the extrapolation based on the earlier measurements (Guidorzi et al., GCN 22534; Heintz et al., GCN 22535; D'Avanzo et al., GCN 22536; Watson et al., GCN 22536; Littlefield & Garnavich, GCN 22538; Strobl et al., GCN 22541; Klotz et al., GCN 22542; Lipunov et al., GCN 22543; Schweyer & Kann, GCN 22544) and indicate a break in the afterglow light curve.