TITLE: GCN CIRCULAR NUMBER: 36777 SUBJECT: GRB 240615A: SAI CMO J- band observations DATE: 24/06/28 12:50:00 GMT FROM: Alexei Pozanenko at IKI, Moscow grb.alex@gmail.com
A. Volnova (IKI), A.A. Tatarnikov (SAI MSU), A.M. Tatarnikov (SAI MSU), N. Pankov (HSE, IKI), A. Pozanenko (IKI), S. Belkin (IKI, HSE) report on behalf of GRB-IKI-FuN:
We observed the field of GRB 240615A (Fermi GBM team, GCN 36671; DeLaunay et al, GCN 36672; Evans, GCN 36673; Frederiks et al, GCN 36677; Tan et al, GCN 36682; Page et al, GCN 36683; Roberts and Meegan, GCN 36685; Kozyrev et al, GCN 36726) 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 2024-06-20, and 2024-06-23. The infrared point source (Busmann et al, GCN 36706) within XRT S1 localization is well detected in stacked images of both epochs at coordinates (J2000) 21:44:23.66, +38:34:08.81 with an uncertainty of 0.1 arcsec in both coordinates.
Preliminary photometry of the source is as follows:
Date UT start t-T0 Exp. Filter OT Err. UL(3 sigma) (mid, days) (s) 2024-06-20 19:39:18 5.10936 46x96.5 J 19.23 0.07 21.1 2024-06-23 21:58:41 8.19335 35x96.5 J 19.76 0.07 21.8
The magnitudes are calibrated against nearby stars of 2MASS and are not corrected for the Galactic extinction.
The light curve fit yields a power law exponent of about -1.0, which is typical for a gamma-ray burst afterglow. We suggest the source is an afterglow of GRB 240615A. Our photometry is consistent with photometry reported early (Kumar et al, GCN 36676, Kumar et al, GCN 36680; Karambelkar et al, GCN 36686; Gupta and Misra, GCN 36696; Busmann et al, GCN 36706; Jiang et al, GCN 36713; Rastinejad et al, GCN 36746, GCN 36751).
Due to the extremely red color of the source, i.e. marginal detection in the i-filter by NOT (Jiang et al, GCN 36713) we tentatively set a lower limit on the redshift of the GRB source of ~4.5. Further observations of GRB 240615A are encouraged.
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