1 Introduction

G 315.4-2.30 (MSH 14-63, RCW 86) is a bright (in both radio and X-ray) shell-like supernova remnant (SNR) with a peculiar protrusion to the southwest (e.g. Dickel et al. 2001; Vink et al. 1997). This protrusion encompasses a bright hemispherical optical nebula (Rodger et al. 1960, Smith 1997; see also Fig. 3). The characteristic angular size of the SNR is about 40', that at a distance to the remnant of 2.8 kpc (Rosado et al. 1996) corresponds to $\simeq$32 pc. The radius of the optical nebula is $\simeq$2' (or $\simeq$1.6 pc). A collection of observational data points to the young age (few thousand years) of the SNR (see e.g. Dickel et al. 2001).

Vink et al. (1997) put forward the idea that the SNR G 315.4-2.30 is the result of a supernova (SN) explosion inside a pre-existing wind-driven cavity (see also Dickel et al. 2001; Vink et al. 2002) and noted that the elongated shape of the SNR resembles that of a wind-driven cavity created by a moving massive star (see Weaver et al. 1977 and Brighenti & D'Ercole 1994 for details). On the other hand, it is believed that the origin of the southwest protrusion is due to the interaction of the SN blast wave with a density enhancement in the ambient interstellar medium. However, as was correctly noted by Dickel et al. (2001), the density enhancement (e.g. a high-density cloud) should result in a concave dent in the shell, not in a protrusion. Dickel et al. (2001) also suggested that this protrusion "is perhaps the key to what is going on".

We agree with the idea that G 315.4-2.30 is a diffuse remnant of an off-centered cavity SN explosion and supplement this idea by the suggestion that the massive SN progenitor star exploded near the edge of the main-sequence bubble. This suggestion implies that the southwest protrusion is the remainder of a bow shock-like structure created in the interstellar medium by the post-main-sequence winds (see Sect. 4 and Gvaramadze 2002; cf. Wang et al. 1993) and that the SN exploded near the center of this hemispherical structure. Given the youth of the SNR and assuming a reasonable kick velocity for the stellar remnant, one can expect that the stellar remnant should still be within the protrusion. Motivated by these arguments, Gvaramadze (2002) searched for a possible compact X-ray source to the southwest of G 315.4-2.30 using the ROSAT archival data, but the moderate spatial resolution of the ROSAT PSPC precluded detection of point sources against the bright background emission of the SNR's shell.

In this paper we report the discovery of two point X-ray sources near the center of the hemispherical optical nebula using the archival Advanced CCD Imaging Spectrometer (ACIS) data of the Chandra X-Ray Observatory. We interpret one of the sources as a foreground active star of late spectral type, and the second one as a candidate stellar remnant (neutron star).

Note that Vink et al. (2000) also reported the discovery of a point X-ray source in the southwest half of G 315.4-2.30, at about 7' from the geometrical center of the SNR. We recall that Vink et al. (1997) suggested that the SN blast wave in this SNR takes on the shape of the pre-existing elongated cavity (created by the stellar wind of the moving SN progenitor star). However, the initially spherical shape of the wind-driven cavity could be significantly affected by the stellar motion only if the massive star reaches the edge of the cavity and the stellar wind starts to interact directly with the ambient interstellar medium (e.g. Weaver et al. 1977); this implies that the SN explodes near the edge of the future (young) SNR (see Sect. 4). However, the source discovered by Vink et al. (2000) is located too far from the edge of G 315.4-2.30. Moreover, the spectral characteristics of the source and the presence of a possible optical counterpart suggest that it is an active star rather than the stellar remnant associated with the SNR (Vink et al. 2000; see also Sect. 3.1).