Speaker
Description
The Einstein Probe mission is rapidly increasing the number of known fast X-ray transients (FXTs), opening a new window on short-lived high-energy phenomena in the Universe. A major open question is whether these FXTs represent the softer and lower-luminosity extension of the classical long gamma-ray burst (GRB) population, or whether they include events belonging to a physically distinct class of transients.
With the growing sample of Einstein Probe detections, systematic comparisons with previously known GRB populations are now becoming possible. In this work, I present a search for MeV and GeV counterparts to FXTs, aimed at assessing whether a significant fraction of these events produces detectable high-energy emission and how this emission relates to their X-ray properties. In particular, I use Fermi-GBM data to search for prompt gamma-ray counterparts, and Fermi-LAT data to place upper limits in cases with no significant detection.
These constraints also provide a way to investigate the broad-band emission of FXTs within synchrotron and synchrotron self-Compton (SSC) frameworks. If some of these transients are powered by relativistic jets, a non-detection in the LAT band may either indicate the absence of the inverse Compton or the inverse-Compton component instead peaks at higher energies, potentially in the TeV band. FXTs may therefore represent promising systems for studying the connection between X-ray transients and very-high-energy gamma-ray emission.
