GCN Circular 32542
Subject
GRB 220831A: Gemini-South Infrared Observations
Date
2022-09-10T20:56:20Z (3 years ago)
Edited On
2024-04-24T15:04:51Z (a year ago)
From
Brendan O'Connor at UMD <oconnorb@umd.edu>
Edited By
Vidushi Sharma at NASA GSFC/UMBC <vidushi.sharma@nasa.gov> on behalf of Leo P. Singer at NASA/GSFC <leo.p.singer@nasa.gov>
B. O'Connor (UMD/GWU), E. Troja (UTV/ASU), S. Dichiara (PSU),
on behalf of a larger collaboration:
We performed target of opportunity observations of GRB 220831A
(Tohuvavohu et al. GCN 32506) with the FLAMINGOS-2 spectrograph
mounted on the Gemini-South telescope. Observations were taken
in the J and Ks filters with total exposure of 1785 and 1635 s,
respectively. The observations began at 2022-09-09 03:27:01 UT,
corresponding to ~8.6 d after the burst. Further observations
were obtained the following night (~9.6 d) in J-band for
2000 s exposure.
At the location of the optical, infrared, and X-ray counterpart
(Dichiara et al. GCN 32510, D'Avanzo et al. GCN 32513, Freeburn
et al. GCN 32516, Gordon et al. GCN 32535), we detect a faint
source with brightness J ~ 24.5 AB mag. This result confirms the
fading of the infrared source reported by D'Avanzo et al.
GCN 32513.
Our measurement implies a very red color, r-J >2, of the late
time emission. At present it is not clear whether this is due
to the onset of a kilonova or to the contribution of an underlying
host galaxy. Assuming a behavior similar to AT2017gfo, the
apparent J-band magnitude implies a distance of ~200 Mpc. However,
the nearby galaxy noted by D'Avanzo et al. GCN 32513 is significantly
closer at only 4 Mpc.
If instead the source is dominated by the host galaxy contribution,
the red color suggests that GRB 220831A was a distant event
(see, e.g., O'Connor et al. 2022, MNRAS, 515, 4890).
Further observations are planned.
Magnitudes are calibrated against stars in the 2MASS catalog
and are not corrected for Galactic extinction.
We thank the staff of the Gemini Observatory, in particular
Joan Font-Serra and Yijung Kang, for rapid scheduling of
these observations.