Spectra were extracted from a circle of 2 arcmin radius. This choice, based on the minimum standard selection radius, reduces the NGC4151 contamination. Particular care has been taken in determining the local background under the source for the strong contamination from NGC 4151 events. We used as background a region of the same shape and size located in the opposite position with respect to the Seyfert. We selected a total of 5592 and 1808 counts in the source and in the background region respectively.
Data are well compatible with a constant.
Spectral analysis has been performed on the spectrum sum of all observations. Counts have been rebinned in order to have at least 20 counts per bin and the matrix relative to the correct off-axis position has been used. The spectrum has been fitted with a power law plus low energy absorption. Figure 2 shows the total spectrum and the residuals from the best fit model. The total spectrum of the source can be fitted by a simple power law of photon spectral index 2.12 0.06.