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GCN Circular 32513

GRB 220831A, VLT/HAWK-I near-infrared observations
2022-09-01T20:48:48Z (2 years ago)
Daniele B Malesani at Radboud U <>
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 
coordinates (J2000):

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.
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