Type II: The PHA Data Extension for multiple datasets

For a number of analysis tasks in which multiple PHA datasets are to be stored and/or analysed simultaneously, it is generally considered cumbersome if each resides in a separate file. This is particularly the case for (say) sub-second, time-resolved spectroscopy when a single observation may give rise to a very large number of datasets. It should be stressed however that this is for datasets from the same instrument. Users wishing to simultaneously analyse PHA data from different instruments should always use multiple input files. Finally, it is worth noting that users who prefer to use the multiple file approach for such analysis (especially if only a small number of datasets are to be considered) can still do so by using the XFLTXXXX keyword described above.

As in the single dataset case, the data will be stored as a BINTABLE extension. However here, vector arrays are used in place of scalars for several columns. Thus the PHA data, errors etc. are vectors and each row contains a single PHA dataset. The other columns list all other parameters which vary between the datasets.