GCN Circular 36777

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
Not found
 
 
; DeLaunay
et al, GCN 36672
Not found
 
 
; Evans, GCN 36673
Not found
 
 
; Frederiks et al, GCN 36677
Not found
 
 
; Tan et al,
GCN 36682
Not found
 
 
; Page et al, GCN 36683
Not found
 
 
; Roberts and Meegan, GCN 36685
Not found
 
 
; Kozyrev et
al, GCN 36726
Not found
 
 
) 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
Not found
 
 
) 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
Not found
 
 
, Kumar et al, GCN 36680
Not found
 
 
; Karambelkar et al, GCN 36686
Not found
 
 
; Gupta and
Misra, GCN 36696
Not found
 
 
; Busmann et al, GCN 36706
Not found
 
 
; Jiang et al, GCN 36713
Not found
 
 
;
Rastinejad et al, GCN 36746
Not found
 
 
, GCN 36751
Not found
 
 
).

Due to the extremely red color of the source, i.e. marginal detection in
the i-filter by NOT (Jiang et al, GCN 36713
Not found
 
 
) we tentatively set a lower
limit on the redshift of the GRB source  of ~4.5. Further observations of
GRB 240615A are encouraged.