- The paper demonstrates that energy-dependent gamma-ray emission in SS 433's jets is produced primarily by inverse Compton scattering.
- The study employs over 200 hours of H.E.S.S. data and a one-dimensional Monte Carlo model to locate electron acceleration sites 25–30 parsecs from the binary system.
- The research reveals that particle transport is dominated by advection with rapid synchrotron cooling, offering fresh insights into jet deceleration and shock dynamics.
Acceleration and Transport of Relativistic Electrons in SS 433's Jets
The paper conducted by the H.E.S.S. Collaboration provides a detailed exploration of the microquasar SS 433, focusing on the intricacies of relativistic electron acceleration and their transport within the parsec-scale jets. Utilizing an extensive dataset from the High Energy Stereoscopic System (H.E.S.S.) totaling over 200 hours, the research delineates the energy-dependent gamma-ray emission morphology from these jets, proposing that high-energy gamma rays are produced predominantly via inverse Compton (IC) scattering of photons by an energetic electron population.
SS 433 is distinguished as a binary system constituted by a likely black hole and an A-type supergiant star, discharging jets at velocities close to a quarter of the speed of light. This system exhibits fascinating dynamics, including precession with a 20° half-opening angle over 162 days. The research integrates these spatial and temporal dynamics to contextualize observations of gamma-ray emissions, extending from 0.8 TeV, delineating a morphological dependency indicative of an energy-dependent gamma-ray production process extending to the jets' extremities.
A primary outcome is the identification of particle acceleration sites some 25 to 30 parsecs from the binary system. The researchers elucidate that shocks arising from the self-collimation of precessing jets serve as efficient sites for electron acceleration to very high energies, with electron energy loss dominated by synchrotron cooling. Observationally, the highest-energy gamma rays (>10 TeV) coincide with the base of the outer X-ray-emitting jets, inferring concentrated acceleration sites at these locations, evoking a challenge to prior interpretations that identified these regions as X-ray knot loci of particle acceleration.
The team postulates that particle transport is governed by advection rather than diffusion, implying that rapid cooling alongside advection limits the travel distance of high-energy electrons. This assertion is bolstered by fitting a one-dimensional Monte Carlo model which incorporates cooling rates and transport dynamics to the spatial distribution of gamma-ray emissions observed.
In modeling these jets, calculations suggest velocities approximating 0.083c at the outer regions, considerably slower than the initial jet launch velocities, implying potential deceleration influenced by jet-environment interactions. The jet expands in size, reducing velocity while preserving incompressible flow, consistent with observational data and theoretical predictions of shock formation and sub-relativistic shock velocities in transonic jets.
Furthermore, the work highlights the systems' contribution to cosmic-ray populations, albeit localized to environments near SS 433 considering typical Galactic diffusion coefficients. These insights position SS 433 as a valuable model for shock acceleration and non-thermal processes in mildly relativistic astronomical jets, offering potential analogs to explain broader astrophysical phenomena observed in extragalactic environments.
Future inquiry may consider refining diffusion and advection models under varying environmental conditions, further elucidating the interplay of microquasar dynamics and shock physics across scales, potentially extending these insights to address the origin of extreme cosmic rays in galactic and extragalactic contexts. This paper contributes significantly to cosmic ray and high-energy astrophysics by advancing comprehension of particle acceleration processes within astrophysical jets.