TITLE:   GCN CIRCULAR
NUMBER:  35956
SUBJECT: X-ray transient EP240315a: PRIME near infrared detection
DATE:    24/03/18 18:35:29 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 Einstein Probe detection (GCN 35931) of EP240315a, we observed the transient field in the J filter with PRIME ~1 day after the Einstein Probe detection.

At the position of the optical transient AT2024eju reported by ATLAS (Srivastav et al. GCN 35932), we detect an uncatalogued source in J band. Using nearby VISTA Hemispherical Survey (VHS) stars for preliminary calibration we derive the following magnitude, not corrected for Galactic extinction:

Filter | Mag(VISTA)     | SNR | Seeing | Total exposure time (s) | UT Date-time at start
-------|----------------|-----|--------|------------------------------------------------
J      | 19.7 +/- 0.3   | 6.0 |  1.3”  | 675                     | 2024-03-16T19:14:20

This result is consistent with GROND detection (Rau GCN 35937). Conditions were intermittently cloudy, resulting in higher than usual photometric error.

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.