TITLE: GCN CIRCULAR NUMBER: 35818 SUBJECT: GRB 240218A: CMO SAI NIR upper limit DATE: 24/02/27 12:04:54 GMT FROM: Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru> A. Volnova (IKI), A. Pozanenko (IKI), B. Safonov (SAI MSU), A. Tatarnikov (SAI MSU), N. Pankov (HSE, IKI), S. Belkin (IKI, HSE) report on behalf of IKI-GRB-FuN: We observed the field of GRB 240218A (Page et al., GCN 35742; Veres et al., GCN 35755; Svinkin et al., GCN 35758) with the Astronomical Near-Infrared Camera-spectrograph (ANC) of the 2.5-meter telescope (SAI-2.5) of the Caucasian Mountain Observatory (CMO SAI) on Feb.23, 2024 starting on 22:16:46 UT, taking 47 frames of 1-minute exposure in the H-band under moderate conditions with seeing of 1.4". We do not detect the NIR counterpart (D'Avanzo et al., GCN 35747; Saccardi et al., 35756; Schroeder et al., GCN 35794; Rossi et al., GCN 35762; de Wet et al., GCN 35765) within the enhanced XRT error box (Evans et al., GCN 35748). Preliminary photometry of the stacked image is following Date UT start t-T0 Filter Exp. OT UL(3sigma) (mid, days) (s) 2024-02-23 22:16:46 5.86743 H 47*59 n/d 20.8 The photometry is based on nearby 2MASS stars: 2MASS_ID RA Dec H errH 10471145+0118146 10:47:11.45808 +01:18:14.6268 15.422 0.098 10471594+0117439 10:47:15.94200 +01:17:43.9836 14.562 0.062 10471583+0116464 10:47:15.83136 +01:16:46.4844 14.243 0.045 View this GCN Circular online at https://gcn.nasa.gov/circulars/35818. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...