- stellar jet L 1551 IRS 5 ( HH 154 )

We have for the first time detected X-ray emission associated with a proto-stellar jet, on the jet emanating from L1551 IRS5. The IRS5 proto-star is hidden beyond 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 L X ≃ 3 × 10 29 erg s −1 , a significant 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 T ≃ 0.5 MK, fully compatible with the temperature expected (on the basis of the jet's velocity) for the shock front produced by the jet hitting the circumstellar medium.