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

96 APPENDIX D. BAT SOFTWARE TOOL REFERENCE
be useful, for example, if each DPH row is to be flattened into a detector image, while otherwise
preserving the individual exposures.
The “matchlc” binning method will bin the input data to match an existing light curve. The
light curve, which is passed in the ‘gtifile’ parameter, must be a standard OGIP light curve file
with enough information to determine the time binning. If the light curve file has a GTI extension,
it is ignored. Note that the ‘minfracexp’ parameter is always honored. If it is important to exactly
match the template light curve time bins, even if they have zero exposure, then set minfracexp=0.
For output light curves, the TIME column may refer to the start or the center of the bin,
depending on the setting of the ‘timepixr’ parameter. Output lightcurves also contain the keyword
TIMEPIXR which indicates the reference point for light curve time bins. For all other output
types, TIME refers to the start of the accumulation time. In some cases, a separate keyword or
column named TSTOP or TIME STOP is used to indicate the stop of the accumulation time.
TIME SELECTION
By default, the input file is selected according to its own internal good time intervals, if any are
present.
Crude time selection can be performed using the tstart and tstop parameters to the task, which
give the start and stop times of accumulation.
More refined selections can be performed specifying the gtifile parameter. A good time interval
file (GTI) describes an arbitrary number of intervals by specifying the start and stop times. The
intersection of the input files’ GTIs, the user-provided gtifile, and the user-provided tstart/tstop
parameters, are used to select input data by time. For input DPH (survey) data, the time interval
of each input DPH must overlap with the total good time intervals by a large enough amount, and
must never straddle more than one output bin.
The DPH overlap time required is determined by the min dph frac overlap, min dph time overlap
and max dph time nonoverlap parameters. Care should be taken when altering the overlap parameters,
especially when the properties of the source and the background are not constant with time.
For example, if a source becomes earth-occulted during the DPH, and a corresponding occultation
GTI was input to batbinevt, then the background will have the full exposure, but the source
will only have a fractional exposure, i.e. the exposure is ambiguous. For exposure purposes, batbinevt
records the full exposure of all DPHs that pass the overlap tests, including any non-overlap
intervals. The output GTI, however, retains the user-requested good time intervals.
FLUX UNCERTAINTIES
batbinevt assumes that detector counts are Poisson-distributed, and propagates the errors to the
output. However, if the input is a modeled background (e.g. from batclean), then the output
uncertainties will be set to zero. This behavior is governed by the HDUCLAS2 keyword in the
input DPH file: modeled background maps should have HDUCLAS2 = ‘PREDICTED’.
D.1.4 PARAMETERS
infile [filename ]
Input file name or names, containing BAT event or DPH data. This may be a commadelimited
list of names, or the name of a text file containing a list of file names, one per line,
preceded by an ‘@’ character.