Speaker
Description
Direct cosmic-ray measurements determine the spectra and composition of charged particles and show that the Galactic spectrum steepens around $\sim 3$ PeV, the so-called knee. This feature is widely taken to mark the energy where typical Galactic accelerators or Galactic confinement begin to fail, but the responsible source class is still unknown. Supernova remnants are the standard candidates, yet their maximum energy is constrained by their finite size, magnetic-field strength, and lifetime, and it remains unclear whether they can account for the highest-energy Galactic cosmic rays.
Ultrahigh-energy gamma-ray observations now point to an additional contender: microquasars, X-ray binaries that launch relativistic jets. V4641 Sgr is a particularly stringent case, with reported gamma rays up to $\sim 800$ TeV and an extended emission region in an unusually low-density environment. Low density makes proton–proton gamma-ray production inefficient, while electron-based scenarios face rapid cooling at PeV energies and difficulty sustaining emission over large scales.
I will present a modelling framework that connects the compact jet to the large-scale gamma-ray halo. We first fit the multi-wavelength emission of the inner jet to constrain the allowed jet power and the spectrum of particles that can escape. We then propagate these particles through the surrounding medium and compare hadronic- and leptonic-dominated explanations against the gamma-ray spectrum and spatial extent. The results are presented as an energy budget and the required particle distributions, identifying which physical conditions make a hadronic component necessary, and where a primarily leptonic origin remains viable.
| Talk category | NOVA Network 3 |
|---|---|
| Second preference | Poster |
