Recollimation boundary layers as X-ray sources in young stellar jets

TL;DR

This paper proposes that recollimation shocks in stellar winds, caused by pressure from disk winds, can produce stationary X-ray emission near young stellar jets' bases, aligning with observations of objects like DG Tau.

Contribution

It introduces a semi-analytical model showing how wind-wind interactions can generate X-ray emission in young stellar jets, supporting a new explanation for observed high-energy phenomena.

Findings

Recollimation shocks can produce X-ray emission consistent with observations.

A specific stellar wind model reproduces DG Tau's X-ray spectrum.

Wind-wind interaction scenario is viable for jet base X-ray emission.

Abstract

Young stars accrete mass from circumstellar disks and in many cases, the accretion coincides with a phase of massive outflows, which can be highly collimated. Those jets emit predominantly in the optical and IR wavelength range. However, in several cases X-ray and UV observations reveal a weak but highly energetic component in those jets. X-rays are observed both from stationary regions close to the star and from knots in the jet several hundred AU from the star. In this article we show semi-analytically that a fast stellar wind which is recollimated by the pressure from a slower, more massive disk wind can have the right properties to power stationary X-ray emission. The size of the shocked regions is compatible with observational constraints. Our calculations support a wind-wind interaction scenario for the high energy emission near the base of YSO jets. For the specific case of DG Tau, a stellar wind with a mass loss rate of $5\cdot10^{-10}\;M_{\odot}\;\mathrm{yr}^{-1}$ and a wind speed of 800 km s$^{-1}$ reproduces the observed X-ray spectrum. We conclude that a stellar wind recollimation shock is a viable scenario to power stationary X-ray emission close to the jet launching point.