TITLE:   GCN CIRCULAR
NUMBER:  37303
SUBJECT: GRB 240825A: PRIME near-infrared detection
DATE:    24/08/26 17:12:41 GMT
FROM:    Joe Durbak at UMD <gcn.joedurbak@gmail.com>

O. Guiffreda (UMD), J. Durbak (UMD), S. Atri (U Rome), A. S. Kutyrev (NASA/GSFC), E. Troja (U Rome), K. De (MIT), S. B. Cenko (NASA/GSFC)

Following the Swift BAT detection (GCN 37274), and Fermi GBM detection (GCN 37273), we observed the transient field in J and H filters with PRIME ~8 hours after FERMI & Swift detection.

At the position of the optical counterpart reported by Swift UVOT (GCN 37274), we detect an uncatalogued source in J and H bands. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitudes, not corrected for Galactic extinction:  

Filter | Mag(AB)      | SNR  | Seeing | Exp. time (s) 
-------|--------------|------|--------|---------------
J      | 18.9 +/- 0.2 | 17.5 | 2.1”   | 600           
H      | 18.5 +/- 0.2 | 34.0 | 2.3”   | 600           

The J-band results are consistent with the REM detection of 17.7 +/- 0.3 Mag(Vega) (GCN 32795) taken an hour later.

Further observations are planned.

PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa at the South African Astronomical Observatory (SAAO) (Kutyrev et al. 2023, Yama et al. 2023).

We thank the Osaka University observers at PRIME and the staff at SAAO for their support with these observations.