TITLE:   GCN CIRCULAR
NUMBER:  31388
SUBJECT: GRB 220101A: 2.2m CAHA (+CAFOS) first day optical detection
DATE:    22/01/04 23:06:26 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

M. D. Caballero-Garcia, R. Sanchez-Ramirez, Y.-D. Hu, A. J. Castro-Tirado, E. Fernandez-Garcia (IAA-CSIC), G. Bergond and I. Hermelo (CAHA) report:

Following the detection of the bright GRB 220101A by Swift (Tohuvavohu et al., GCNC 31347), Fermi (Arimoto et al., GCNC 31350, Lesage et al., GCNC 31360) and AGILE (Ursi et al., GCNC 31354) we observed the optical afterglow (Kuin & Tohuvavohu, GCNC 31351; Fu et al., GCNC 31353; Hentunen et al., GCNC 31356; Perley, GCNC 31357; de Ugarte Postigo et al., GCNC 31358; Vinko et al., GCNC 31361; Tomasella et al., GCNC 31363; Mao et al., GCNC 31364; Noschese et al., GCNC 31366; Mao et al., GCNC 31368; Nicuesa Guelbenzu et al., GCNC 31370; Strausbaugh et al., GCNC 31371; D'Avanzo et al., GCNC 31373; Strausbaugh et al., GCNC 31383; Dimple et al., GCNC 31384; Romanov, GCNC31387) with the CAFOS instrument, mounted on the 2.2 m telescope, at the Calar Alto Observatory (Almeria, Spain). The observation started at 18:12:07 UT on 1st January 2022 (13.78 hr after the GRB) and consisted of 3 x 60 s, 4 x 60 s and 1 x 300 s exposures in the sdss_i, sdss_r and sdss_g bands. Against comparison stars from SDSS, we measure r=19.75+-0.05 for the GRB 220101A optical afterglow.

We thank the staff at Calar Alto observatory for their excellent support.