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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 is 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 other
parameters which may vary between the datasets. The notation below
is the same as that used in description of the type I data format.
- Num, a 2-byte INTEGER scalar giving the reference number
of the spectrum stored in this row.
The FITS column name is SPEC_NUM.
(unitless).
- Channel, a 2-byte or 4-byte INTEGER array containing the channel
numbers for the spectra in the Data column.
- Data, either:
- a 2-byte or 4-byte INTEGER array containing the number of counts
observed in all channels during this time interval;
- or a 4-byte REAL array containing the number of counts
per second observed in all channels during this time interval.
In both cases the notation is as for the type I data.
- Stat_err, a 4-byte REAL array giving the statistical error on
the values within Data.
- Sys_err, a 4-byte REAL array giving the
fractional systematic error to be applied to each value
within Data.
- Qual, a 2-byte INTEGER array giving the data
quality flag for each value within Data.
- Grpg, a 2-byte INTEGER array giving the data data
grouping flag for each channel.
- Rowid, an (optional) CHARACTER string giving a
unique identifier for each spectrum. The FITS column name is
ROWID.
- Exposure, a 4-byte REAL scalar or array giving the
exposure time for each spectrum.
The FITS column name is EXPOSURE
- AreaSc, a 4-byte REAL scalar or array giving the
area scaling factor to be applied.
The FITS column name is AREASCAL
- Bkgdfile, a CHARACTER string
giving the name of the background file (if any) associated with
the dataset contained in Data.
The FITS column name is BACKFILE
- BackSc, a 4-byte REAL scalar or array giving the
scaling factor to be applied to Bkgdfile.
The FITS column name is BACKSCAL
- Corrfile, a CHARACTER string
giving the name of the correction file (if any) associated with
the dataset contained in Data.
The FITS column name is CORRFILE
- Corrscal, a 4-byte REAL giving the
scaling factor to be applied to Corrfile.
The FITS column name is CORRSCAL
- Respfile, a CHARACTER string
giving the name of the redistribution matrix file (RMF)
associated with the dataset contained in Data.
The FITS column name is RESPFILE
- Ancrfile, a CHARACTER string
giving the name of the ancillary response file (ARF; if any)
associated with the dataset contained in Data.
The FITS column name is ANCRFILE
Points to Note & Conventions
(in addition to those given in the section on type I data)
- In addition to those listed the following keywords may appear as
columns : XFLTXXXX, DATE-OBS, TIME-OBS, DATE-END, TIME-END.
- As with all OGIP files, any of the above variables which have the same
value in every row can be removed from the table, and specified as a
keyword within the header. Here this is most likely in the case of
EXPOSURE, AREASCAL, BACKFILE, BACKSCAL, CORRFILE, CORRSCAL, RESPFILE, and ANCRFILE.
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Last modified: Thursday, 21-Oct-2021 12:50:38 EDT
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