uvotproduct is a tool which creates level III science products (specifically a light-curve) from the level II images, combining images until significant detections are reached (c.f. uvotmaghist). Running the script produces a plot of the light-curve in all filters in which data were collected, together with a corresponding FITS file and a text file containing a report of the output. One or more sky images are required as the input (a single *sk.img or *sk.img.gz file, a comma-separated list of images or @filenames where filenames is a file with the name of one sky image on each line), together with the source position. The start time (T0) is also required though, in the case of the Swift-triggered GRB, the tool will use the
TRIGTIME keyword in the header of the file. If this keyword is not present, the command
timezero=xxxxxxxxx.x should be included on the command line, where
xxxxxxxxx.x is the T0 in Swift MET.
>uvotproduct Name of input image file : @filenames Source region file : 5arcsec.reg Background region file : back.reg Name for output report or NONE[ : report.txt BAT position : NONE XRT position : NONE UVOT position : NONE Ground position : NONE Name for output magnitude history plot or NONE : maghist.gif Name for output magnitude history : maghist.fits
The source region file is required; the BAT, XRT and UVOT position can all be set to NONE without detrimental effect. The background region file can be set to DEFAULT, meaning that the background will be extracted from an annulus centred on the source region (inner radius 12.5 arcsec; outer radius 25 arcsec), with 6 arcsec exclusion regions for any sources detected within (or overlapping) the background annulus.
Data points are combined until the requested detection significance is reached. By default, adjacent points are merged until a signal-to-noise ratio of 2 is reached; to increase this to 3,
rebin=MIN_SIGMA=3,SNR_DIFF=3.5 should be included on the command line. There is also a MAX_TIME_RATIO parameter (the default is also 2), which means that the next data point will not be combined with the previous one if the ratio of the new end time to the start time exceeds this value. Similarly, MIN_TIME_RATIO means that even significant detections will be combined if they are very close together in time. Note that these sub-parameters (MIN_SIGMA, SNR_DIFF etc) are combined on the command line using a comma as the delimiter.
The output magnitude history FITS file (maghist.fits in the above example) contains information about count rates, fluxes and magnitudes; the maghist.gif plots magnitude light-curves by default. This can be changed to count rates by including
plotmag=no on the command line. By default, the white, b, u and v filters will be plotted together (maghist1.gif), while maghist2.gif will show uvw1, uvw2 and uvm2. These can be combined into a single plot using the command
plotfilters=white,b,u,v,uvw1,uvw2,uvm2. The report.txt file lists the files used and gives the relevant magnitudes and upper limits, together with the significance of the unbinned and binned-up data.
fhelp uvotproduct for more details.