TITLE:   GCN CIRCULAR
NUMBER:  33449
SUBJECT: GRB 230307A: GECKO optical observations and detections of the afterglow
DATE:    23/03/10 07:42:47 GMT
FROM:    Myungshin Im at Seoul Nat U  <mim@astro.snu.ac.kr>

Myungshin Im, Gregory S.-H. Paek, Mankeun Jeong, Seo-Won Chang, Hyeonho
Choi (SNU), and Chung-Uk Lee (KASI)

We covered the localization areas of GRB 230307A (GBM team GCN 33405, Xiong
et al. GCN 33406) with the RASA36 telescope at the El Sauce observatory in
Chile, and the KMTNet telescopes in SSO, Australia, and SAAO, South Africa.
The RASA36 observation started at 2023-03-08-00:52 (UT) or about 9.11 hrs
after the burst alert, taking a series of r-band images for about 20 min.
The starting times of the KMTNet SSO and SAAO stations are 2023-03-08-09:39
(UT) and 2023-03-08-18:30 (UT) or 17.89 hrs and 26.74 hrs respectively,
taking a series of R- and I-band images for about 1 hr at each location.

We clearly identify the afterglow (Levan et al. GCN 33439, Lipunov et al.
GCN 33441, O'Conner et al. 33447) and confirm its fading nature in all of
the time-series KMTNet images, with the photometry roughly consistent with
that of the Levan et al. (GCN 33439) report. A weak signal is found in the
RASA36 image.
Further observations and analysis are being carried out.

We thank the KMTNet operators for their support for the KMTNet observations.