The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

106 APPENDIX D. BAT SOFTWARE TOOL REFERENCE
the PSF-fitting stage for intensity only (unless posfit=NO). Additional detected sources are also
written to the output catalog.
This task can operate on multiple images, as produced by batfftimage. If the images vary
only in their energy range, and are otherwise identical in their coordinate systems and exposures,
then the ‘vectorflux’ parameter can be set to YES. When vectorflux=YES, each source has only
one catalog row, and multiple fluxes are recorded in a vector table cell. When vectorflux=NO, a
source will appear multiple times in the catalog, with a single flux in each entry. Note that if the
input images do not match exactly their coordinate system or exposures, then you must specify
vectorflux=NO.
To avoid spurious detections at the edge of the field of view, a partial coding threshold can be
specified (see ‘pcodefile’ and ‘pcodethresh’). If a partial coding map is provided, then by default
sources must be at least 1% coded.
This routine uses a relatively straightforward brute-force convolution by FFT to compute the
sliding-cell averages. Users should have a about a factor of eight more memory than the size of the
image.
Fitting For Position and Flux
batcelldetect has several options to fit the positions and fluxes of sources. Newly detected and
previously known sources are treated differently. By default, the positions of newly detected sources
are allowed to vary and the those of previously known sources are held fixed. This behavior depends
on the input parameters and the input catalog.
The following behaviors are possible:
srcfit=NO Perform source detection only. The positions and fluxes for all sources are not fit. For
new sources, the positions are taken from the source detection stage. For previously known
sources, the values are transferred from the input catalog completely unchanged.
srcfit=YES; posfit=NO (DEFAULT) Hold the position of known sources fixed, but fit for the
positions of new sources. The fluxes of all sources are fitted.
srcfit=YES; posfit=YES; posfitwindow=0.0 Fit for the positions of all sources. The positions
of known sources are allowed to vary within a window which is 3 times the ERR RAD
value from the input catalog. Thus, if ERR RAD = 0, the position is held fixed. Special
cases: if an individual value of ERR RAD is null, the position of that source is allowed to
vary. If the ERR RAD column is missing entirely, the positions are assumed to be fixed. The
fluxes of all sources are fitted.
srcfit=YES; posfit=YES; posfitwindow > 0 As above, except the positions of known sources
are allowed to vary by ± 3*ERR RAD or ± posfitwindow, whichever is larger.
As of May 2007, the BAT team recommends using the GAUSSIAN point spread function
(FWHM=0.37413) for all BAT data throughout the mission. The previous recommendation to use
the “PYRAMID” shape was not correct.
D.2.4 CATALOG OUTPUT
The output catalog contains the following columns. Other input columns are copied to the output
unchanged. For new sources entries, the row is filled with null value before writing batcelldetectderived
quantities.