The gas density around SN 1006 - AstrophysicsReport as inadecuate

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Abstract: The density of the ambient medium where the supernova remnant evolves is arelevant parameter for its hydrodynamical evolution, for the mechanism ofparticle acceleration, and for the emission at TeV energies. Using XMM-NewtonX-ray observations, we present a study of the ambient medium density of thehistorical supernova remnant SN 1006. We modelled the post-shock thermalemission to constrain the ambient medium density. Our study is focused on theNorth-West and the South-East rims of the remnant, where the thermal emissiondominates. We used a plane-parallel shock plasma model plus another componentfor the ejecta that are not negligible in the regions of our study. Theimportance of the synchrotron component is also studied. In order to improvestatistics, we combined several observations of the remnant.The density found in the South-East rim is low, roughly 0.05 cm-3, and seemsto be representative of the rest of the remnant. However, in the North-West rimclose to the bright optical filament, the density is significantly higherabout 0.15-0.25 cm-3. This confirms a picture of SN 1006 evolving in atenuous ambient medium, except in the North-West where the remnant has recentlyencountered a denser region.A density this low is compatible with the non-detection of the remnant by theHESS gamma-ray observatory. The lower density in the South-East implies ahigher shock speed of 4900 km-s, higher than that of 2890 km-s measured in theNorth-West. This new estimate of the velocity could increase the maximum energythat accelerated particles can reach to energies of about 1 PeV.

Author: F. Acero, J. Ballet, A. Decourchelle


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