DOI

https://doi.org/10.48717/vx6v-8c25

Project

EW053

Title

{EVN+eMERLIN observations of GRB 250702BDE at 4cm}

Abstract

The proposal targets the exceptional transient GRB 250702BDE/EP250702a, which shows hour-scale, multi-episode gamma-ray activity, a hard spectrum, and an off-nuclear, heavily obscured host, defying standard GRB/transient classes. We have already secured compact radio detections with e-MERLIN (5.07 GHz) and e-EVN (4.9 GHz) at milliarcsecond scales. To discriminate among an ultra-long/structured GRB, a relativistic WD–IMBH TDE, and a precessing/multi-jet engine, we request two VLBI epochs combining 1.7 GHz (EVN+MeerKAT), 5.0 GHz (EVN+e-MERLIN), and 8.4 GHz (EVN), coordinated with contemporaneous ATCA SED coverage. The program requests a total of 32 hours. Our aims are to build late-time SEDs, constrain compactness and brightness temperature, and measure size/centroid evolution and any late-time re-energization, thereby deriving decisive constraints on energetics, geometry, and microphysics. Under a slow-decay model, our sensitivity forecasts indicate > 11sigma detections in all bands and epochs, ensuring robust, model-discriminating outcomes.