Context: .Protostellar jets are a new class of X-ray sources which has been discovered with both XMM-Newton and Chandra. The mechanism responsible for the X-ray emission is still not clear. Self-shocking in jets, shocks where the jet hits the surrounding medium, reflected or scattered stellar X-ray emission have all been invoked as possible explanations. Aims: .One key diagnostic discriminating among physical emission mechanisms is the motion of the X-ray source: hydrodynamical numerical models of continuous protostellar jets plowing through a uniform medium show an X-ray emitting shock front moving at several hundreds km s-1. In the nearest X-ray emitting protostellar jet, HH 154, this is detectable, with the spatial resolution of the Chandra X-ray observatory, over a few years baseline, allowing a robust discrimination among different mechanisms. Methods: .We have performed, in October 2005, a deep Chandra X-ray observation of HH 154. Comparison with the previous (2001) Chandra observation allows to detect proper motion down to the level predicted by models of X-ray emitting shocks in the jet. Results: .The 2005 Chandra observation of HH 154 shows unexpected morphological changes of the X-ray emission in comparison with the 2001 data. Two components are present: a stronger, point-like component with no detectable motion and a weaker component which has expanded in size by approximately 300 AU over the 4 years time base of the two observations. This expansion corresponds to approximately 500 km s-1, very close to the velocity of the X-ray emitting shock in the simple theoretical models. Conclusions: .The 2005 data show a more complex system than initially thought (and modeled), with multiple components with different properties. The observed morphology is possibly indicating a pulsed jet propagating through a non-homogeneous medium, likely with medium density decreasing with distance from the driving source. Detailed theoretical modeling and deeper X-ray observations will be needed to understand the physics of this fascinating class of sources.
Favata, F., Bonito, R., Micela, G., Fridlund, M., Orlando, S., Sciortino, S., et al. (2006). The discovery of an expanding X-ray source in the HH 154 protostellar jet. ASTRONOMY & ASTROPHYSICS, 450, L17-L20.
|Data di pubblicazione:||2006|
|Titolo:||The discovery of an expanding X-ray source in the HH 154 protostellar jet|
|Citazione:||Favata, F., Bonito, R., Micela, G., Fridlund, M., Orlando, S., Sciortino, S., et al. (2006). The discovery of an expanding X-ray source in the HH 154 protostellar jet. ASTRONOMY & ASTROPHYSICS, 450, L17-L20.|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1051/0004-6361:20065106|
|Appare nelle tipologie:||1.01 Articolo in rivista|