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Astron. Astrophys. 342, 839-853 (1999)

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ROSAT PSPC observation of the NE region of the Vela supernova remnant

III. The two-component nature of the X-ray emission and its implications on the ISM

F. Bocchino, A. Maggio and S. Sciortino

Osservatorio Astronomico di Palermo "G.S. Vaiana", Palazzo dei Normanni, I-90134 Palermo, Italy

Received 13 July 1998 / Accepted 13 October 1998

Abstract

We reconsider two ROSAT observations of the Vela SNR shock region, with the aim to overcome the problems encountered in interpreting the X-ray spectra in terms of single-temperature NEI emission model. We pursue the idea of the association of the observed cool and hot components with an high-density ("inhomogeneities") and a low-density ("intercloud") ISM phase, respectively. We derive the density (0.5-1.0 cm-3) and the volume filling factor (0.2-0.8) of the inhomogeneities on a scale length of [FORMULA] ([FORMULA] pc), and we identify two regions of the main shock interactions, one with a small ([FORMULA] pc) isolated cloud, and the other with a larger feature ([FORMULA] pc, perhaps a cavity wall). We argue that the thermal evaporation from shocked clouds may account for the mass of observed inhomogeneities. After isolating the emission of the dynamically unperturbed intercloud medium, we apply the Sedov analysis and estimate the explosion energy of the supernova event ([FORMULA] erg) and the distance ([FORMULA] pc, in agreement with recent results). Our data also indicate fast electron-ion equipartition behind the shock. The influence of Non-Equilibrium of Ionization effects on our conclusions are estimated.

Key words: X-rays: ISM – ISM: supernova remnants – ISM: structure – ISM: individual objects: Vela supernova remnant – ISM: general – ISM: clouds

Send offprint requests to: bocchino@oapa.astropa.unipa.it

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999
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