TITLE:   GCN CIRCULAR
NUMBER:  34467
SUBJECT: GRB 230815A: VLT/HAWK-I near-infrared afterglow detection
DATE:    23/08/17 16:41:24 GMT
FROM:    Benjamin Schneider at MIT <bschn@mit.edu>

B. Schneider (MIT), A. Chrimes (Radboud), D. B. Malesani (Radboud and DAWN/NBI), 
A. J. Levan (Radboud), N. R. Tanvir (U. Leicester), A. de Ugarte Postigo (OCA/CNRS), 
report on behalf of the Stargate collaboration:

We observed the field of GRB 230815A (Klingler et al., GCN 34434; 
Mailyan et al. GCN 34440) with the ESO Very Large Telescope, equipped 
with the HAWK-I near-infrared camera. Observations consisted of two 
epochs of 20 min exposure in the H band at 23:19:53 UT on 2023-08-15 
(~12.5 hr after trigger) and 23:15:46 UT on 2023-08-16 (~36.4 hr after 
trigger).

In both epochs, we clearly detected two sources consistent with the XRT 
error circle (Beardmore et al., GCN 34437). One of the sources has 
significantly faded (~2 mag) between the two epochs, evolving from 
AB mag = 20.11 +/- 0.02 to AB mag = 22.01 +/- 0.08. This corresponds 
to a power-law decay index of 1.65,  similar to the X-ray decay rate, 
suggesting a small host contribution to the NIR flux. The proposed 
afterglow of the burst is detected at coordinates:

RA (J2000) = 12:18:53.24
DEC (J2000) = -58:03:09.45

with an uncertainty of 0.3".

We acknowledge the excellent support provided by the Paranal staff, 
in particular Joe Anderson.