Discovery of X - ray emission from the protostellar jet L 1551 IRS 5 ( HH 154 )

We have for the first time detected X-ray emission associated with a protostellar jet, on the jet emanating from the L1551 IRS5 protostar. The IRS5 protostar is hidden behind a very large absorbing column density, making the direct observation of the jet’s emission possible. The observed X-ray emission is likely associated with the shock “working surface”, i.e. the interface between the jet and the circumstellar medium. The X-ray luminosity emanating from the jet is moderate, at LX ' 8 × 10 erg s−1, a fraction of the luminosity normally associated with the coronal emission from young stars. The spectrum of the X-ray emission is compatible with thermal emission from a hot plasma, with a temperature of ' 0.5 MK, fully in line with the temperature expected (on the basis of the jet’s velocity) for the shock front produced by the jet hitting the circumstellar medium.