TITLE:   GCN CIRCULAR
NUMBER:  31442
SUBJECT: GRB 220101A: continued 1.3m DFOT optical observations of a high-redshift afterglow
DATE:    22/01/12 11:11:42 GMT
FROM:    Amit Kumar at ARIES, India  <amitkundu515@gmail.com>

Amit Kumar, Rahul Gupta, Amit Ror, Ankur Ghosh, Dimple, Amar Aryan, Brajesh
Kumar, S. B. Pandey, and K. Misra (ARIES) report:

We further observed the optical afterglow of the Swift detected GRB 220101A
(Tohuvavohu et al., GCN 31347) at z = 4.618 (Fu et al., GCN 31353; Fynbo et
al., GCN 31359) with the 1.3m Devsthal Fast Optical Telescope (DFOT) at
Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital
(India), from 2022-01-03 UT 12:54:68 to 2022-01-03 UT 15:04:14 (from ~55.75
to 57.91 hours after the burst). We obtained 40 frames each of 120 seconds
in Bessell R and I filters. We clearly detected the optical afterglow of
GRB 220101A in stacked frames within the Swift XRT enhanced error circle
(Tohuvavohu et al., GCN 31347) as also reported by Kuin & Tohuvavohu, GCN
31351; Fu et al., GCN 31353; Hentunen et al., GCN 31356; Perley, GCN 31357;
de Ugarte Postigo et al., GCN 31358; Fynbo et al., GCN 31359; Vinko et al.,
GCN 31361; Tomasella et al., GCN 31363; Mao et al., GCNs 31364, 31368;
Noschese et al., GCN 31366; Guelbenzu et al., GCN 31370; Strausbaugh et
al., GCNs 31371, 31383, 31389; Dimple et al., GCN 31384; Romanov, GCN
31387; Caballero-Garcia et al., GCN 31388; Belkin et al., GCN 31390; Ror et
al., GCN 31394; Avanzo et al., GCN 31395; Pankov et al., GCN 31398;
Guelbenzu et al., GCN 31401; Moskvitin et al., GCN 31420; and Perley, GCN
31425.

The estimated preliminary magnitudes for the R and I-band images are as
follows:

T_start-T0(hours)           Filter           Magnitude (mag)
-----------------------------------------------------------------------
55.75                              I                   19.52 +- 0.02
57.91                              R                   20.95 +- 0.04

Aperture photometry is performed, and calibration is done based on the
standard stars in the USNO-B1.0 catalogue. The quoted magnitudes are not
corrected for the Galactic extinction in the direction of GRB 220101A.

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