Radial Spectra

To save time analysing different sections of an extended object, it is possible to produce a single file containing spectra at a number of different radii. For instance a circular cluster, centred on the optical axis, of extent 0.5 degrees, could be divided into 5 radial rings of width 0.1 degrees. To produce such a source file select a circular source box in xrtsort of radius 0.5 degrees, and select axes 7 and 8 at the BIN_AXIS prompt. As with extended sources, it is best to subset the data by restricting the Master Veto Rate range to 170.

The subtraction should be performed as for an extended source, e.g. an annular background region of radius 0.7-0.8 degrees might be appropriate. xrtsub and xrtcorr will then background subtract and exposure correct all the spectra in one go.

If xspec is used for spectral fitting, each spectrum may be converted individually with ast2xsp. The ASTERIX spectral fitting software will work directly on a radial set of spectra, the desired spectra may be selected with sdata before using sfit.