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

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2. The data

Two pointed X-ray observations of the North and North-East rim of the Vela supernova remnant have been carried out with the Position Sensitive Proportional Counter on-board ROSAT (Trümper 1983). Table 1 summarizes the relevant information about the two sequences (RP200133 and RP500015). RP200133 (PI Sciortino) has been already studied in Paper I and in Paper II, while the public archive sequence RP500015 (PI Kahn) has been chosen to extend the coverage of the Vela outer shell in our spatially resolved spectral analysis. We recall that the PSPC has a circular field of view of [FORMULA] diameter, and its spatial resolution is [FORMULA] FWHM on axis and [FORMULA] FWHM at [FORMULA] off-axis, while the spectral resolution is [FORMULA] at 1 keV. Fig. 1 shows the ROSAT All-Sky Survey observation of the Vela SNR, with the position of the two sequences over-imposed. In order to remove high background time intervals from the X-ray observation, we have run the optimized time-screening algorithm of Bocchino et al. (1998) on both sequences: in Table 1 we report the screened and unscreened exposure times. The exposure maps have been recomputed according to the procedure of Snowden et al. (1994). The spatial grid used for spatially resolved spectral analysis consists of sectors and rings (Fig. 2), and was introduced in Paper II for RP200133. In particular, the outermost ring corresponds to the [FORMULA] radius circle introduced by Aschenbach (1993, also reproduced in Fig. 1), which encloses the Vela SNR diffuse emission.


Table 1. The RP200133 and RP500015 PSPC sequences
a We report the exposure time before and after the application of the time screening algorithm of Bocchino et al. (1998).
b Number of counts in the whole field of view.

[FIGURE] Fig. 1. The Vela SNR in the ROSAT 0.1-2.4 keV All-Sky Survey. Small circles mark the position of the PSPC sequences RP200133 and RP500015, whereas the large [FORMULA] radius circle encloses the Vela SNR diffuse emission (adapted from Aschenbach 1993).

[FIGURE] Fig. 2a and b. Spatial distribution of 0.2-2.0 keV surface brightness of RP200133 (left panel ) and RP500015 (right panel ) PSPC sequences. 1.0 and 4.0 [FORMULA] cnt s- 1 arcmin-2 contours which marks the background, diffuse emission and clumps regions defined in Sect. 3.1 are overlaid. Grayscale is linear from 0 to 8.0 [FORMULA] cnt s- 1 arcmin-2. North is up and East is on the left.

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999