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Astron. Astrophys. 360, 671-682 (2000)

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5. Conclusions

The BeppoSAX observations of RCW86 confirm that this remnant has different properties at different location in its shell, shedding more light on the nature of the differences. In particular, the N region shows X-ray properties indicating a Sedov shock interacting with the environment. The ROSAT spectrum is consistent with this picture and in addition seems to show a supersoft component ([FORMULA] keV). If this component is real, we suggest that the Sedov-like properties correspond to the expansion inside a cavity wall, and that the shock has very recently encountered the wall of this cavity, giving rise to the supersoft component. Detailed spatially-resolved spectral analysis is required to exactly locate the supersoft component and to confirm this scenario. We have derived the abundances in this region and we have found that they are fully consistent with a metal-depleted ISM behind the shock in which grain destruction is occurring. Applying the Sedov analysis to the X-ray data, we find a distance of [FORMULA] kpc and an age of [FORMULA] yr, if the initial explosion energy was [FORMULA] erg. While we can probably rule out lower E, we cannot formally exclude a more energetic event on the basis of the North rim observations alone, which would require the remnant to be further away ([FORMULA] kpc) and older ([FORMULA] yr).

The emission from the SW rim (the "knee") is very different, since two temperature components ([FORMULA] and [FORMULA] keV) are required to describe the data. Moreover the global metallicity of the high-T component ([FORMULA]) are well above the cosmic abundances, suggesting that the hard SW emission mainly comes from stellar ejecta. The overall picture is consistent with the ejecta/CSM scenario discussed by Borkowski et al. (1996) for Cas A. The fact that different locations of the same SNR are described by very different models (as if they were different SNRs) is not really surprising, because it is well know that RCW86 is a highly inhomogeneous object. We argue that spatial variations of the X-ray spectral emission of the "knee", as shown by the hardness ratio map in Fig. 4 (right panel), are well modeled by variations of the emission measure ratio of the two X-ray components, and, by using a formalism developed by Bocchino et al. (1999), we have estimated a filling factor of the high-T component [FORMULA] in the soft X-ray regions and [FORMULA] in the other SW regions. We have estimated an upper limit of the swept-up mass not directly related to the ISM, and we point out that the progenitor SN must be of Type Ia if we adopt the canonical [FORMULA]. Moreover, the detection of the emission from ejecta favors the [FORMULA] solution in Table 7, which is compatible with the connection with SN185, thus weakening the also proposed connection of a more evolved RCW86 with a more distant OB association at 2.8 kpc.

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© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000