{
  "subject": "GRB 250814A: CMO SAI and SAO RAS izJ observations.",
  "submittedHow": "web",
  "submitter": "Alina Volnova at IKI RAS <alinusss@gmail.com>",
  "createdOn": 1755781743403,
  "format": "text/plain",
  "bibcode": "2025GCN.41465....1V",
  "body": "A. Volnova (IKI), A. Moskvitin (SAO RAS), A. Pozanenko (IKI), N. Pankov (HSE, IKI), P. Minaev (IKI), S. Kotov (SAO RAS), A.M. Tatartnikov (SAI MSU), V.K. Postnikova (SAI MSU) report on behalf of IKI-GRB-FuN:\n\nWe observed the field of GRB 250814A detected by Swift/BAT and Fermi/GBM (Caputo et al. GCN  Circ. 41358; Fermi team, GCN Circ. 41357) and possibly associated with the sub-threshold GW trigger S250814bg (LVK, GCN Circ. 41364) with 2.5-meter SAI-25 telescope of the Caucasian Mountain Observatory of Sternberg Astronomical Institute (SAI CMO), equipped with the IR camera ASTRONIRCAM. The observations in the J-filter were carried out on 2025-08-16 starting UT 23:20:51. We also observed this field  with the BTA 6-m telescope of SAO RAS, equipped with the Scorpio-2 multi-mode focal reducer (Afanasiev & Moiseev,  2011, BaltA, 20, 363), and obtained series of images in SDSS i,z bands on 2025-08-17 starting 20:47:31 UT.\n\nThe two NIR sources reported previously (Karambelkar et al. GCN Circ. 41377; Castro-Tirado et al., GCN Circ. 41381; Ahumada et al. GCN Circ. 41382; Pankov et al. GRB Circ. 41389; D'Avanzo et al. GCB Circ. 41391; Kumar et al. GCN Circ. 41392; D'Avanzo et al. GCN Circ. 41408) are clearly detected. The preliminary photometry of the sources Source 1 and Source 2 according to D'Avanzo et al. (GCB Circ. 41391) is:\n\ndate    |UT start|t-T0,d |Filter|Exp,s|Source 1   |Source 2   |UL3sigma|FWHM\"|Telescope/Site\n=========================================================================================\n25-08-16|23:20:51|2.68958|J     |4224 |21.72(0.07)|21.96(0.08)|22.9    |1.2  |SAI-25/CMO\n25-08-17|20:47:31|3.56255|z     |1200 |22.39(0.04)|22.46(0.04)|24.2    |1.4  |BTA/SAO\n25-08-17|21:25:21|3.58647|i     |1200 |23.39(0.05)|23.31(0.05)|24.6    |1.4  |BTA/SAO\n\nAll magnitudes are in AB system and not corrected for the Galactic extinction. The photometry is calibrated using Pan-STARRS i,z magnitudes and 2MASS J magnitudes for the following stars:\n\nRA          Dec          i_PS1         z_PS1         J_2MASS*\n20:25:12.01 +48:24:08.4  16.924(0.004) 16.703(0.008) 15.750\n20:25:17.82 +48:24:04.6  17.234(0.003) 16.952(0.005) 15.627\n* - J magnitudes of the reference stars are in Vega system.\n\n(We are grateful to the management of the observatories for observational time and the staff for excellent observations.)",
  "circularId": 41465,
  "eventId": "GRB 250814A"
}