Alternative Spectral Extraction from the Mosaic

Read this if you want to extract the average spectrum of a source from a set of mosaic images in different energy bands.

It is possible to extract the spectrum of a source from a set of mosaic images (in several large energy bands). In general this method gives results similar to the Science Window average spectrum you obtain from spe_pick (see Sections and ). Once you have the spectrum, you will need the corresponding rebinned matrix to be able to analyse it in XSPEC. We suggest to build such a matrix before launching OSA as shown in Section and then extract images with the use of this matrix as shown in Section . See Sections and to learn how to create mosaic images (for a better flux estimate use OBS1_PixSpread=0).

Once you have the set of mosaic images in the desired energy bands, to extract the spectrum from the mosaics (attached to the og_ibis.fits file!) at the position of 4U 1700-377 (ra=255.9865, dec=-37.84414) use mosaic_spec:

cd $REP_BASE_PROD/obs/xxx
mosaic_spec DOL_inp="og_ibis.fits" DOL_out="og_ibis.fits"\
EXTNAME="ISGR-MOSA-IMA" DOL_spec="4U1700_mosa_pha.fits(ISGR-PHA1-SPE.tpl)"\
ra=255.9865 dec=-37.84414 size=4

Note that if the significance of the point is less than five, then mosaic_spec will assign a non-zero value to its quality, and the point will be not used by XSPEC. If you are interested to see this point do change its quality value to zero manually. You find more details on mosaic_spec in Section .

Please, remember, that with OSA 10.2, different ARFs should apply to spectra extracted from the data of different observation periods, while in OSA 11, different response matrices should be used. Below, ARF applies to OSA10.2, RMF to OSA11. If the mosaic, from which you have extracted spectra, contains the data from more than one observation period, none of the pre-defined ARFs/RMFs can be used with the spectra generated with mosaic_spec. Instead, a special ARF/RMF, averaged proportionally to the exposures from different periods should be generated. The simplest way to do this is to run the standard ScW by ScW spectral extraction for your source (even if the source is not detected in individual ScWs) and then use the spe_pick command (see Section ) which, among others, will produce the exposure-weighted average ARF/RMF for your particular data set.