TITLE: GCN CIRCULAR NUMBER: 35633 SUBJECT: GRB240122A: PRIME near infrared detection DATE: 24/01/25 20:05:40 GMT FROM: Joe Durbak at UMD gcn.joedurbak@gmail.com

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

Following the MAXI/GSC detection (Negoro et al. GCN 35593), GOTO optical candidate GOTO24eu/AT2024apy (Kumar et al. GCN 35596), and the Swift afterglow detection (Ambrosi et al. GCN 35600), we observed the transient field using J and H filters with PRIME ~1.5 days after MAXI/GSC detection.

At the position of the optical counterpart detected by GOTO, we detect an uncatalogued source in both J and H bands. Using nearby 2MASS stars for preliminary calibration we derive the following magnitudes, not corrected for Galactic extinction:

Filter | Mag(AB) | SNR | Seeing | Total exposure time (s)

-------|----------------|-----|--------|-------------------------

J | 21.02 +/- 0.20 | 6.3 | 1.373” | 1802

H | 20.90 +/- 0.21 | 6.1 | 1.480” | 1544

PRIME is a 1.8m telescope with 1.56 square degree FOV (0.5 arcsec/pixel) located in Sutherland, South Africa.

Further observations are planned.

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

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