X-ray emission mechanisms in protostellar jets

Abstract

Prompted by the recent detection of X-ray emission from Herbig-Haro objects, we studied the interaction between a supersonic jet originating from a young stellar object and the ambient medium; our aim is to investigate the mechanisms causing the X-ray emission. Our model takes into account the radiative losses from optically in plasmas and Spitzer's thermal conduction including saturation effects. We explored the parameter space defined by the density contrast between the ambient medium and the jet and by the Mach number, to infer the configurations which can give rise to X-ray emission. From the models, we derived the X-ray emission as it would be observed with Chandra/ACIS-I and XMM-Newton/EPIC-pn, using the MEKAL spectral code and including the absorption of interstellar medium. Here we discuss a representative case which produces, without any ad hoc assumption, Xray emission with characteristics very similar to those observed in the protostellar jet, HH 154. We find that the X-ray emission originates from a blob localized just behind the bow shock, moving with velocity 500 km/s. We predict, therefore, among other features, a detectable proper motion of the X-ray blob, which is interesting for future observations.