GCN Circular 41943

Subject

GRB 250920C: PRIME near-infrared detection

Event

GRB 250920C

Date

2025-09-22T20:28:38Z (20 hours ago)

Edited On

2025-09-22T20:36:06Z (20 hours ago)

From

O. Guiffreda at UMD <oriogui@umd.edu>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov>

Via

Web form

O. Guiffreda (UMD), J. Durbak (UMD), A. S. Kutyrev (NASA/GSFC), N. Passaleva (U Rome), M. El Kabir (U Rome), E. Troja (U Rome), S. B. Cenko (NASA/GSFC)

Following the Fermi GBM (GCN 41903

) and Swift BAT (GCN ), we observed the transient field in Z, Y, J and H filters with PRIME ~7 hours after the initial Fermi and Swift detection.

At the position of the optical counterpart reported by GOTO (GCN 41907

), we detect an uncatalogued source in all aforementioned bands. Using nearby 2MASS and PanSTARRS stars for preliminary calibration we derive the following magnitudes and limits, not corrected for Galactic extinction:

Filter	Mag(AB)
Z	19.7 +/- 0.10
Y	19.7 +/- 0.07
J	18.8 +/- 0.10
H	18.0 +/- 0.07

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, Durbak et al. 2024).

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