GRB 221009A: Gemini-South Infrared Afterglow Detection

We performed target of opportunity observations of GRB 221009A (Dichiara et al., GCN 32632, Veres et al., GCN 32636) with the FLAMINGOS-2 spectrograph mounted on the Gemini-South telescope. Observations began on October 13, 2022 at 23:58:42 UT corresponding to ~4.4 d after the GRB. We obtained images in the JHK filters with a total exposure of 60 s in each. The target was at airmass 1.75 under seeing of ~0.7". The afterglow is clearly detected in the JHK filters. We obtain the following magnitudes calibrated against the 2MASS catalog: J = 17.93 +/- 0.03 AB mag H = 17.23 +/- 0.05 AB mag K = 16.69 +/- 0.02 AB mag Compared to previous nIR photometry (Brivio et al., GCN 32652, Durbak et al. GCN 32654), our observation yields a power-law decay with index ~ -1.4. This is steeper than reported in the optical (O'Connor et al., GCN 32739) and consistent with that observed in X-rays. These magnitudes are not corrected for Galactic extinction. Further infrared observations are planned. We thank the staff (Janice Lee, Jennifer Andrews, and Jeong-Eun Heo) of the Gemini Observatory for rapidly approving and scheduling these observations.