TITLE:   GCN CIRCULAR
NUMBER:  37250
SUBJECT: EP240820a: PRIME J-band Observations
DATE:    24/08/23 20:26:09 GMT
FROM:    Joe Durbak at UMD <gcn.joedurbak@gmail.com>

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

Following the Einstein Probe detection (GCN 37214), we observed the fast X-ray transient field in J-band with PRIME ~51 hours after the EP/WXT detection.  The total exposure time in J-band was 1800s.

At the candidate position given by EP/FXT, we detect no uncatalogued sources in J-band. Using nearby VISTA Kilo-Degree Infrared Galaxy Survey (VIKING) stars for preliminary calibration we derive the following limiting magnitudes, not corrected for Galactic extinction:  


Filter | Mag (Vega)     | Total exposure time (s) 
-------|----------------|-------------------------
J      | >21.3          | 1800

There is a galaxy within the FXT error radius found in the Dark Energy Survey (DES) catalogs located at 16.2450, -34.6941 (J2000) with a photo-z of 0.402+/-0.088.

The observed J-band brightness of this galaxy is 19.356 +/- 0.19 Vega, which is marginally brighter than the cataloged VIKING brightness of 19.784 +/- 0.0948 Vega.

Further observations to assess variability 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.