TITLE:   GCN CIRCULAR
NUMBER:  41372
SUBJECT: GRB 250814A: J-band upper limit from WINTER
DATE:    25/08/14 15:52:22 GMT
FROM:    Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197@gmail.com>

Viraj Karambelkar (Caltech), Tomas Ahumada (Caltech), Benjamin Schneider
(LAM), Robert Stein (UMD), Geoffrey Mo (MIT),  Danielle Frostig (CfA),
Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech)
report:

We observed the field of the Fermi and Swift GRB 250814A (Fermi team, GCN
Circ. 41357, Caputo et al. GCN  Circ. 41358) coincident with the
sub-threshold GW trigger S250814bg (GCN Circ. 41364) in the near-infrared
with the Palomar 1-m telescope, equipped with the 1-square degree WINTER
camera (Lourie et al. 2020, Frostig et al. 2024). Observations started on
2025-08-14 at 07:49:52 UT (15 min after the trigger) and consisted of 15
exposures of 120 s in the J-band.

In the stacked image, we do not detect any new source at the X-ray
afterglow position reported by Caputo et al, GCN 41358 down to the
following 5-sigma AB magnitude:

J > 19.3

The images were processed using the WINTER data reduction pipeline
implemented with mirar (https://github.com/winter-telescope/mirar,
https://doi.org/10.5281/zenodo.13352565). The photometric calibration was
performed using nearby stars from the 2MASS catalog and the magnitude is
not corrected for Galactic extinction.

WINTER (Wide-field INfrared Transient ExploreR) is a partnership between
MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF
AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute
for Astrophysics and Space Research.