2024/07/25 by R. Ricci, Ricci, R., E. Troja +17 · 4 citations
Engineering · Physics and Astronomy · #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Particle Accelerators and Free-Electron Lasers #Particle Detector Development and Performance #Superconducting Materials and Applications
paper · pdf · doi:10.48550/arxiv.2407.18311
openalex publication_date 2024/07/25 · openalex created_date 2024/09/30 · openalex updated_date 2026/07/28
The recent launch of Einstein Probe (EP) in early 2024 opened up a new window onto the transient X-ray sky, allowing for real-time discovery and follow-up of fast X-ray transients (FXRTs). Multi-wavelength observations of FXRTs and their counterparts are key to characterize the properties of their outflows and, ultimately, identify their progenitors. Here, we report our long-term radio monitoring of EP240315A, a long-lasting (∼ 1000 s) high redshift (z=4.9) FXRT associated to GRB~240315C. Our campaign, carried out with the Australian Telescope Compact Array (ATCA), followed the transient's evolution at two different frequencies (5.5 GHz and 9~GHz) for three months. In the radio lightcurves we identify an unusual steep rise at 9 GHz, possibly due to a refreshed reverse shock, and a late-time rapid decay of the radio flux, which we interpret as a jet break due to the outflow collimation. We find that the multi-wavelength counterpart of EP240315A is well described by a model of relativistic jet seen close to its axis, with jet half-opening angle θj ≈ 3 ∘ and beaming-corrected total energy E ≃ 4× 1051~erg, typical of GRBs. These results show that a substantial fraction of FXRTs may be associated to standard GRBs and that sensitive X-ray monitors, such as Einstein Probe and the proposed HiZ-GUNDAM and Theseus missions, can successfully pinpoint their relativistic outflows up to high-redshifts.