GCN Circular 32750

B. O'Connor (UMD/GWU), E. Troja (UTV/ASU), S. Dichiara (PSU),
J. Gillanders (UTV), S. B. Cenko (NASA/GSFC):

We performed target of opportunity observations of GRB 221009A
(Dichiara et al., GCN 32632
Not found
 
 
, Veres et al., GCN 32636
Not found
 
 
)
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
Not found
 
 
,
Durbak et al. GCN 32654
Not found
 
 
), 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
Not found
 
 
) 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.