P. D'Avanzo (INAF/OABr), A. Rossi (INAF/OAS), D. B. Malesani (Radboud
and DAWN/NBI), S. Campana (INAF/OABr), A. J. Levan (Radboud univ.)
report on behalf of the Stargate collaboration:
Following the report of the Swift/BAT/GUANO GRB 220831A (Tohuvavohu et
al., GCN 32506; see also Wood & Meegan, GCN 32511) we observed the BAT
error circle with the ESO Very Large Telescope, equipped with the HAWK-I
near-infrared camera. Observations consisted in 20 min exposure in the J
band, with a mean time of 19.4 hr after the GRB.
Lacking a deep reference image to check for variability, no claim of a
new object can be made based solely on our data. Within the BAT error
circle, several objects are apparent in the HAWK-I image which are not
visible in the the Legacy survey (z and r bands), which are likely due
to color effects.
A source is visible in the HAWK-I image which is consistent with the
weak X-ray source reported by Dichiara et al. (GCN 32510), at
RA = 01:37:00.95
Dec = -41:35:34.37
Its Vega magnitude is J = 21.9 +- 0.09, calibrated against one 2MASS
star, and is not detected in the Legacy survey down to limiting
magnitudes z > 23.1, r > 24 (all AB).
We also note the presence of the nearby galaxy NGC 625, with a NED
distance ~4 Mpc, which is 23.6 arcmin (~30 kpc in projection) away from
the BAT coordinates of GRB 220831A.
We acknowledge the support of the observing staff at Paranal. Further
observations are planned.