TITLE:   GCN CIRCULAR
NUMBER:  36113
SUBJECT: GRB 240414A: Mondy optical observations
DATE:    24/04/15 13:04:11 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) report on behalf of GRB-IKI-FuN:

We observed the field of GRB 240414A (Caputo et. al., GCN 36083) at redshift z=1.833 (Adami et al., GCN 36085; de Ugarte Postigo et al., GCN 36087) with 1.5-meter AZT-33IK telescope of Sayan observatory at Mondy. The observations were started on 2024-04-14 (UT) 13:56:41, i.e. ~12 hr since the Swift trigger. We took 45 frame 120 s each in the R-filter.
The optical counterpart (Schneider et al., GCN 36084; Adami et al., GCN 36085; de Ugarte Postigo et al., GCN 36087; Niwano et al., GCN 36088; Lipunov et al., GCN 36095; Dutton et al., GCN 36097; Peretto, GCN 36100; Turpin et al., GCN 36101; Karambelkar et al., GCN 36103) is well detected in the stacked image at coordinates of (J2000) 12:19:08.09 +56:44:28.8. Preliminary photometry of the optical source is following:

Date       UT_start  t-T0     Filter Exp.  OT    err  UL(3sigma)
                    (mid, days)     (s)
2024-04-14 13:56:41  0.51395  R     44*120 20.60 0.12 22.2

The magnitudes were calibrated with respect to nearby USNO-B1.0 stars.
Assuming no spectral evolution between earlier observations(Turpin et al., GCN 36101),  we  estimate a power law decay index to be alpha~1.2, which is in agreement with SkyNet observations (Dutton et al., GCN 36097).