TITLE:   GCN CIRCULAR
NUMBER:  32749
SUBJECT: GRB221009A: Gemini-South Optical Afterglow Detection
DATE:    22/10/14 01:58:41 GMT
FROM:    Jillian Rastinejad at Northwestern Univ.  <jillianrastinejad2024@u.northwestern.edu>

J. Rastinejad and W. Fong (Northwestern) report on behalf of a larger collaboration:

We observed the location of GRB 221009A (Dichiara et al. GCN 32632) with the Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-South under Program GS-2022B-DD-103 (PI: Rastinejad). We obtained 7x60-sec imaging in i-band at a mid-time of 2022 October 14 00:40:12 UT  (4.437 days post-burst), at a median airmass of 1.9. We clearly detect the optical afterglow. Calibrated to Panstarrs, we measure a brightness of i ~ 19.8 AB mag at seeing < 0.8'', not corrected for Galactic extinction. This is consistent with recently reported measurements (e.g. Bikmaev et al. GCN 32743) and indicates significant fading from the i-band measurement of 15.58 +/- 0.03 AB mag reported by de Wet et al. (GCN 32646) at 0.178 days. 

Further observations are planned to monitor the variability of the source. We thank Jennifer Andrews, Janice Lee, and additional Gemini staff for the rapid DDT approval, as well as the planning and execution of these observations.