GCN Circular 37480

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

We observed the field of GRB 240912A (Fermi GBM Team, GCN 37465
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; Evans et al., GCN 37466
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; Pawar et al., GCN 37473
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; Smith et al., GCN 37478
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) in the near-infrared J-band with the Palomar 1-m telescope, equipped with the 1 square degree WINTER camera (Lourie et al. 2020). 

Observations began at 2024-09-12T10:58:40 UTC (~9.2 hours after the GRB) and consisted of 15 x 120 s exposures. The images were processed using the WINTER data reduction pipeline (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565
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). 

We do not detect a source at the optical and refined Swift/XRT counterpart location (Evans et al., GCN 37466
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; de Ugarte Postigo et al., GCN 37469
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; Goad et al., GCN 37470
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; An et al., GCN 37471
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; Pérez-Fournon et al., GCN 37476
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; Lipunov et al., GCN 37477
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; Burrows et al., GCN 37479
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). We obtain the following 5-sigma upper limit: J ~ 18.7 mag (AB).

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 Lucille Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.