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\subsection{Models for high-energy emission from stellar jets}  \label{sect:intromodel}  When \citet{2001Natur.413..708P} discovered X-ray emission in HH~2, they immediately discussed strong shocks in the outflow as the most likely heating process and the most obvious way to generate a strong shock is a bow shock at the head of the outflow, where the jet encounters circumstellar material. Depending on the density contrast between the jet and the ambient material, the the forward shock that is driven into the ISM or the reverse shock that travels against the flow in the jet possesses higher shock velocities. However, in most YSO jets, we see the X-ray emission fairly close to the source, where the ISM has been cleared by outflow activity a long time ago. \citet{2003ApJ...584..843B} study the X-ray emission from \object{L1551 IRS 5}, a binary protostar. They suggest several classes of models. First, the observed X-rays might be stellar emission, that is scattered into our line-of-sight by circumstellar material. This requires high densities to reach the required scattering efficiency and the material must be neutral, otherwise it would show up as bright radio emission, which is not seen coincident with the X-ray detection in YSO jets. L1551~IRS~5 \citep{2003ApJ...584..843B}. In DG~Tau this scenario can be excluded because the lightcurve for the soft X-ray emission is flat, while coronal flares are seen in the hard-X-rays \citep{2011ASPC..448..617G}. If the soft X-rays were scattered stellar emission, they should display the same lightcurve.  Second, a time variable launching velocity would cause shocks to propagate along the jet, continuously heating the jet material they encounter. This scenario is confirmed for an optical knot in the jet of HD~163296 \citep{2013A&A...552A.142G}, but the velocity differences are too small to heat the jet to X-ray emitting temperatures. Third, fast shocks form when the jet encounters an obstacle. In the absence of dense ISM this could be a collimation shock, the disk, or the outflow of another star. Jets are typically ejected roughly perpendicular to the disk \citep[e.g.][for IRS 5]{2002A&A...382..573F}, making an interaction with the disk surface unlikely. The interaction with the outflow of a second YSO on scales of a few hundred AU only works in binary systems, such as IRS~5, but X-rays are also detected from stars that are apparently single, such as DG~Tau and RY~Tau. A forth possibility is magnetic heating from the reconnection either between two interacting outflows \citep{2008A&A...478..453M} or from fields that are frozen into the outflow \citep{2013A&A...550L...1S}. In this article, we will analytically explore how a recollimation shock can explain stationary X-ray emission from jets. Based on the observational evidence for multi-layered jets, we assume that the innermost component of the flow is a stellar wind, which is collimated by the disk wind. Collimation shocks of this kind have not been treated in detail in the literature, while X-ray emission due to a moving shock has been studied by several authors \citep[see, e.g.\ the analytical work and numerical simulations by][]{2002ApJ...576L.149R,2007A&A...462..645B,2010A&A...517A..68B}.