uvotevtlc - make a background subtracted light curve from UVOT event data


uvotevtlc infile outfile srcreg bkgreg


This task makes a light curve from UVOT event files. It performs region selection and background subtraction. The user can supply custom time bins using the gtifile parameter. Both source and background regions must be supplied. Complex region files are permitted.

To make sure the UVOT events have been converted to sky positions using the best available Swift spacecraft attitude, the task 'coordinator' should first be run on the event file, with an aspect-corrected attitude file that contains the ajumpapp keyword set to 'T'.

The user has a choice of binning styles via the "timebinalg" parameter. Binning can be either "U"niform, indicating constant bin sizes, or "G"TI, meaning the user choses the bin edges explicitly with a good time interval file. Each separate good time interval will be turned into one output light curve time bin. The good time interval file is also used for time-based filtering of UVOT events.

Output lightcurves contain the keyword TIMEPIXR which indicates the reference point for light curve time bins. For light curves, the start, stop and center times of each bin are given by the TSTART, TSTOP, MET columns respectively. The TIME column corresponds to the center of the bin optionally shifted by an amount controlled by the basetime parameter. The FRACEXP column gives the fractional exposure of this row (a value from 0.0 to 1.0). This is the intersection of the user and file GTIs, and the time interval of the row.

Region-based filtering is done using standard region files (this uses the region filtering capability built into CFITSIO). The user should supply both source and background regions. uvotevtlc calls uvotsource for photometry calculations.

uvotevtlc makes several scratch data files. Users should have enough free space to accomodate these files. The actual size of the scratch data varies depending on the size of the source and background region, but should never be more than the size of the original event files (when they are uncompressed).


infile [filename]
The name of the input events file.

outfile [filename]
The name of the output light curve file

srcreg [filename]
The name of the source region file. Complex regions are permitted.

bkgreg [filename]
The name of the background region file. Complex regions are permitted.

(gtifile = "NONE") [string]
The name of a GTI file. When timebinalg='g', this file can be a GTI which contains custom time bins, one bin per good time interval. If no GTI file is specified, the time bins will be taken from GTI HDUs of infile. If gtifile is not NONE, it is used to time filter the events for all time binning algorithms.

(timedel = 10) [real]
The time bin size in seconds if timebinalg='u'.

(timebinalg = "g") [string]
The time binning algorithm. Either "u" for uniform time binning (constant time bin size specified by 'timedel'); and "g" for custom time binning (specified by 'gtifile').

(tstart = "INDEF") [string]
Optional global start time (MET seconds), or INDEF to use the input file's start time.

(tstop = "INDEF") [string]
Optional global stop time (MET seconds), or INDEF to use the input file's stop time.

(basetime = "INDEF") [string]
This parameter controls the values written to the TIME column. The default value INDEF results in TIME being populated with MET times. The special value TRIGTIME results in TIME being populated with times relative to the TRIGTIME keyword value. The special value KEY:XXX results in TIME being populated with times relative to the value of the keyword XXX. It is an error if the keyword requested is not present in the EVENTS extension or does not have a real number value. Finally, the user can enter an arbitrary MET using the format digits.digit(s), for example '1234567890.132'.

(deadtimecorr = "NO") [string]
Has dead time correction already been applied? This parameter is passed through to uvotsource for use in photometry.

(frametime = "DEFAULT") [string]
UVOT frame time, in seconds, or DEFAULT. This parameter is used to estimate dead time and coincidence loss.

(zerofile = CALDB) [filename]
Name of zero points file or CALDB.
(coinfile = CALDB) [filename]
Name of coincidence loss correction file or CALDB.
(psffile = CALDB) [filename]
Name of point-spread function file or CALDB.
(lssfile = CALDB) [filename]
Name of large scale sensitivity file or CALDB or NONE.
(sensfile = CALDB) [filename]
Name of detector sensitivity loss file or CALDB or NONE.
This parameter is passed to uvotsource.

(fwhmsig = -1) [real]
This parameter is passed to uvotsource.

(subpixel = 8) [integer]
Sub-pixelling level. This parameter is passed to uvotsource.

(clobber = NO) [boolean]
If the output file already exists, then setting "clobber = yes" will cause it to be overwritten.

(chatter = 2) [integer, 0 - 5]
Controls the amount of informative text written to standard output. Setting chatter = 1 produces a basic summary of the task actions; chatter = 2 (default) additionally prints a summary of input parameters; chatter = 5 prints debugging information.

(history = YES) [boolean]
If history = YES, then a set of HISTORY keywords will be written to the header of the specified HDU in the output file to record the value of all the task parameters that were used to produce the output file.


1. Creates a light curve using custom time bins specified by absolute.gti

     uvotevtlc sw00176918992uvvpo_uf.evt src.reg bkg.reg gtifile=absolute.gti




June 2010