TITLE:   GCN CIRCULAR
NUMBER:  35980
SUBJECT: X-ray transient EP240315a: e-MERLIN radio observations
DATE:    24/03/26 14:45:28 GMT
FROM:    Gabriele Bruni at INAF <gabriele.bruni@inaf.it>

G. Bruni (INAF-IAPS), L. Rhodes (Oxford), L. Piro, G. Gianfagna, A.L. Thakur (INAF-IAPS), J. Bright, F. Carotenuto, S. Smartt, R. Fender (Oxford), P. Jonker (Radboud) report:

We observed the new Fast X-ray Transient EP240315a (Zhang et al., GCN 35931) with the e-Merlin radio telescope under the projects DD17003 (PI: Piro) and DD17004 (PI: Rhodes) at 5 GHz for a total of ~16 hours using a combination of two runs in two consecutive nights (from ~17:30 UT to ~02.00 UT, on March 20 and 21, 2024). 

3C286 was used for flux scale calibration, and 0933-0819 for complex gain, respectively. The beam size was 275x104 milli-arcsec. Data was reduced with the e-MERLIN pipeline and imaged with CASA. The image RMS was 15 uJy/beam. 

We did not find statistically significant emission at a level above 5-sigma at the position of the optical counterpart (AT2024eju, Srivastav et al., GCN 35932). Thus, we estimated a 5-sigma upper limit of 75 uJy at 5 GHz. Scintillation could be a possible explanation for the large variability with respect to the previous radio detection at the same frequency (Leung et al., GCN 35968).

Further e-Merlin observations are planned. We thank the e-Merlin staff for their excellent support.