deletions | additions       diff --git a/jets_x ray.tex b/jets_x ray.tex  index 370b00f..20d270a 100644  --- a/jets_x ray.tex  +++ b/jets_x ray.tex 
...
\label{sect:introxray}  In some jets there is evidence for another, hotter and faster component. X-rays were first seen in the jet \object{HH 2} \citep{2001Natur.413..708P,2012A&A...542A.123S}, where the central star is invisible. Later, X-ray emission was also discovered from less enbedded CTTS, \object{RY Tau} \citep{2014ApJ...788..101S} and, most notably, \object{DG Tau}. DG~Tau is the best case to study X-ray emission from the jet close to the star for two reasons: (i)~No other jet driving young stellar object has been observed as often in X-rays. DG~Tau 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} and has been observed with \emph{XMM-Newton} in 2004 \citep{2007A&A...468..353G} and in 2012 \citep{SchneiderDGTauXray}. (ii)~DG~Tau itself is hidden behind a column density of $N_{\textrm{H}}=2\times10^{22}\textrm{ cm}^{-3}$ \citep{2008A&A...478..797G}, which absorbs any soft X-ray emission from the central star. Hard, coronal emission pierces through the gas and allows us to pinpoint the stellar position to high accuracy, while the soft X-rays observed close to the stellar position must come from the jet.  We can distinguish three different X-ray emitting regions in the DG~Tau system: 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. Second, weak and soft emission from the jet is resolved several hundred AU from the star itself.  Third, additional  soft X-rays are emitted in a region about 30-40~AU above close to, but not from  the plane of star, because they are subject to a much smaller absorbing column density than  the accretion disk. central, coronal source.  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 \citep{2008A&A...488L..13S,2011ASPC..448..617G}. The temperature of this inner emission region is remarkably stable over one decade between 3 and 4~MK; the maximum change observed is about 25\,\%. The change in luminosity is 1.6 in the same time range ($L_X=1-2\times10^{30}\textrm{ erg s}^{-1}$) \citep{SchneiderDGTauXray}. There is no reason to believe that the DG~Tau system represents exceptional physical conditions for jet launching. While the inclination and absorption are less favorable to observe X-ray emission very close to the star for other CTTS systems, there are indications that \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} and that the X-ray emission in the more massive Herbig Ae/Be star \object{HD 163296} is extended in the direction of the jet by a few dozen AU, too \citep{2005ApJ...628..811S,2009A&A...494.1041G,2013A&A...552A.142G}.