TITLE: GCN CIRCULAR NUMBER: 36199 SUBJECT: GRB240418A - Candidate afterglow from NIRES DATE: 24/04/20 19:35:35 GMT FROM: Viraj Karambelkar at Indian Inst of Tech,Bombay Viraj Karambelkar (Caltech), Kaew Tinyanont (NARIT), Sam Rose (Caltech), Tomas Ahumada (Caltech), Robert Stein (Caltech), Nathan Lourie (MIT), Danielle Frostig (MIT), Geoffrey Mo (MIT), Robert Simcoe (MIT), Mansi Kasliwal (Caltech) We observed the field of the long GRB 240418A (GCN 36162; GCN 36166; GCN 36177; GCN 36184) in the near-infrared K-prime band with the NIRES acquisition camera on the Keck II telescope starting at UTC 2024-04-19T09:56:00 (~14 hours since trigger). The observations lasted for 300 sec. (25 sec, 12 coadds). We find an uncataloged source at RA = 239.3744, Dec = 23.5961 that is 3.1 arcsec from the centroid of the GRB position and within its 3.6 arcsec localization (from GCN 36166). This source has m_Kp ~ 20.9 +/- 0.1 mag (AB). There is no source at this location in an archival Ks-band image from the UKIRT hemisphere survey (Lucas et al. 2008), and a deep optical image from the Legacy Survey. However, we note that our NIRES observations are more sensitive than the archival UKIRT observations, so it is possible that the NIRES source is an unrelated background source. We also observed this source in the J-band with the WINTER camera on the Palomar 40-inch telescope (Lourie et al. 2021) on 2024-04-19T09:00:14 and did not detect it to a limiting magnitude of m_J ~ 19 mag. Further observations are encouraged.