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\section{Introduction}   In many areas of astrophysics compact central objects accrete mass and angular momentum from a disk and at the same time they eject a highly collimated jet. This is seen for central objects as massive as AGN or as light as (proto) brown dwarfs. For objects like AGN or accreting neutron stars the jets reach relativistic energies while the velocities are significantly lower in young stellar systems.   A large number of jets is observed in near star forming regions, where the jet composition and structure can be studied in great detail \citep[see the review by][]{http://adsabs.harvard.edu/abs/2014arXiv1402.3553F}.  Jets are launched from the early stages of star formation until the accretion from the circumstellar disk ceeds. Jets from very young stars (class I) are the most powerful and can be traced for long distances up to a parsec from the source, but the central engine is still deeply embedded in a dense envelope of gas and dust and thus cannot be observed directly. As the young stellar objects evolve, mass from the envelope becomes thinner and accretes onto the circumstellar disk. In this stage young, low-mass stars that actively accrete from their circum-stellar disk are called classical T Tauri stars \citep[for a review see][]{2013AN....334...67G}. Their jets often only reach a few hundred AU (and are thus sometimes called ``mircojets'' in comparison to the outflows from younger objects), but the lower column density makes the jet acessibly to observations just a few tens of AU from the central star.  Young, low-mass stars It seems reasonable to suspect  that actively accrete the same physics governs the launching  from a circum-stellar disk are called classical T Tauri stars \citep[for a review see][]{2013AN....334...67G}. The slowest velocities are observed in molecular lines with typical line shifts any type  of only a few km~s$^{-1}$ \citep{2008ApJ...676..472B}. These molecular outflows have wide opening angles around 90$^{\circ}$ \citep[e.g.][]{2013A&A...557A.110S,2014A&A...564A..11A} young star  and are presumably launched from that  the disk. Faster components same processes occur close to the lauch site, but observationally the inner few tens of AU  are seen in H$\alpha$ or only accessable  in optical forbidden emission lines such as [\ion{O}{1}] or [\ion{S}{2}]. \citet{2000ApJ...537L..49B} observed CTTS, thus we need to concentrate on CTTS jets to study  the initial properties before a  jet from interacts with  the ambient medium. Recently, there has been increasing evidence that jets from  CTTS \object{DG Tau} with seven long-slit exposures of \emph{HST}/STIS to resolve have a stationary hot (in  the kinematic structure MK range) emission region only a few tens  of AU from  the jet both along and perpendicular central star (Section~\ref{sect:introxray}). In this article, we want  to study  the jet axis. They find that the faster jet components are better collimated and propose scenario of a starionary recollimation shock as  an ``onion''-like scenario, where explanation for this component. While X-ray emission has been discussed in the literature (Section~\ref{sect:intromodel}), starionary recollimation shocks have not been investigated in detail as sources of high-energy radiation. X-rays trace  the fastest jet and most energetic  components make up of jets. They can also influence the chemistry deep in  the innermost layer disk \citep[e.g.][]{http://adsabs.harvard.edu/abs/2010ApJ...714.1511H,http://adsabs.harvard.edu/abs/2012ApJ...756..157G} because they penetrate deeper than UV and optical radiation  and thus alter  the surrounding layers have progressively lower velocities away environment of planet formation. Unlike stellar X-ray emission, the radiation  from the jet axis. The fastest velocities seen in optical emission lines are typically 200-300~km~s$^{-1}$ \citep{2004Ap&SS.292..651B,2008ApJ...689.1112C,2013A&A...550L...1S}. originates above the plane of the disk and thus reaches the entire disk surface, while stellar radiation may be shadowed by the inner disk rim.  Yet, in some jets from CTTS there is evidence for another, more energetic, component. The best studied case is DG~Tau that was the target of several shorter \emph{Chandra} exposures in 2004, 2005, and 2006 and a large program in 2010 \citep{2005ApJ...626L..53G,2008A&A...478..797G,2011ASPC..448..617G}. These observations showed X-ray emission from three distinct regions: First, weak and soft emission from the jet is resolved several hundred AU from the star itself. Second, hard emission from the central star is observed with stellar flares as seen on many other young and active stars. Since the star itself is embedded in circumstellar material, the stellar soft X-ray emission is expected to be completely absorbed. However, soft X-rays very close to the star are observed; they are emitted in a region about 30-40~AU above the plane of the accretion disk. The centroid of the spatial distribution of soft X-rays is consistent with a position on the jet axis 30-40~AU from the star, but the uncertainties on the position would also allow an off-axis emission region \citep{2008A&A...488L..13S}. The luminosity and temperature of this inner emission region are remarkably stable over one decade. The maximum change observed is about 25\,\% \citep{SchneiderDGTauXray}.  DG~Tau is the best observed case, but a similar scenario probably applies to other jet launching young stars, e.g.\ \object{HH 154} also shows an inner, stationary X-ray component and additional emission in the knots \citep{2010A&A...511A..42B,2011A&A...530A.123S}. In the more massive Herbig Ae/Be star \object{HD 163296} there are indications that the X-ray emission is extended in the direction remainder  of the jet by a few dozen AU, too \citep{2005ApJ...628..811S,2013A&A...552A.142G}.  In \citet{2009A&A...493..579G} (from now on ``paper I'') introduction  we showed that this inner X-ray emission can be explained by shock heating of a jet component moving with 400-500~km~s$^{-1}$. For the case of DG~Tau the mass flux in this component is less than $10^{-3}$ of the total mass flux in the jet or even lower if the same material is reheated in several consecutive shocks. If the density in the fast outflow is $>10^5$~cm$^{-3}$ then the cooling length review observational properties  of this shock is only a few AU and in the optical it would be unresolved and outshined by the more luminous emission jets  from the more massive, but slower jet component. However, the stationary nature of the X-ray emission remained unexplained in this scenario.  In this article we explain how such a shock can be caused by the recollimation of the inner jet due to the shape of the boundary between stellar winds CTTS  and disk winds similar to the work of \citet{2012MNRAS.422.2282K} summarize theoretical explantions  for relativistic jets. This scenario naturally explains the stationary appearance and its location within this emission in  the jet collimation region. literature.  In section~\ref{sect:model} we develop the equations that govern the standing  shock front and discuss the physical parameters in section~\ref{sect:parameters}. In section~\ref{sect:results} we present our results and discuss implications in section~\ref{sect:discussion}. We summarize this work in section~\ref{sect:summary}.