TITLE:   GCN CIRCULAR
NUMBER:  37212
SUBJECT: EP240816a: PRIME upper limits
DATE:    24/08/21 00:15:13 GMT
FROM:    O. Guiffreda at UMD <oriogui@umd.edu>

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

Following the Einstein Probe detection (GCN 37188), we observed the fast X-ray transient field in both the J and H filters with PRIME ~22 hours after the EP/WXT detection.  The total exposure time in J band was 1800s, while the total exposure time in H band was 1000s.  

At the candidate positions given by EP/FXT, we detect no uncatalogued sources in either J or H band. Using nearby VISTA Hemispherical Survey (VHS) and 2MASS stars for preliminary calibration we derive the following limiting magnitudes, not corrected for Galactic extinction:  

Filter | Mag(AB)        | Total exposure time (s) 
-------|----------------|-------------------------
J      | >20.9          | 1800
H      | >21.0          | 1000

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.