NAME

cmadead -- corrects EXOSAT CMA lightcurves and images for deadtime

USAGE

cmadead infile evtfile outfile

DESCRIPTION

This task calculates the deadtime for data taken with the EXOSAT CMA detector and applies the correction to the input file, which is either a lightcurve or an image file. Several effects contribute to the total deadtime correction for the CMA instrument. The most important is a telemetry limitation imposed by the requirements of the other onboard instruments and by the background variability of the CMA itself. As a consequence, not all the events collected by the telescopes in conjunction with the CMA detectors were transmitted on ground. This correction varies enormously and depends on the observation length. A second source of deadtime is due to the electronic but this is typically quite small compared to the 'telemetry deadtime'. 'cmadead' accounts for both. To correct for the telemetry loss, 'cmadead' uses the OBC_PACKET extension in the event file, where the number of samples and the arrival time of each data packet are recorded. Therefore the original event file(s) used to extract the image or the source lightcurve are necessary input file(s) to calculate the correction. The deadtime calculation is based on routines (EXP3 for the lightcurve and EXPP for the image) from the EXOSAT Interactive Analysis software package. For a lightcurve, 'cmadead' calculates the deadtime for each bin, applies the correction to the RATE and ERROR columns, and overwrites the FRACEXP column.The average deadtime correction, due to telemetry losses and electronic, is written in the keyword DEADC. DEADAPP is set to true after correction has been applied. The output lightcurve will contain only bins where fractional exposure is above a minimum threshold. The default threshold is set to 0.3 therefore only bins with at least 30% exposure after deadtime correction are output. The threshold can be changed using the parameter minexpo. For an image file 'cmadead' calculates an average deadtime for the entire time interval. The correction is applied to the EXPOSURE keyword. In addition DEADAPP is set to true and the average value is stored in DEADC.

PARAMETERS

infile (input lightcurve or image file) [string]

Name of the file to correct for the deadtime. The input file can be either a lightcurve or an image file. Only one input file is accepted for each run.

evtfile (input event file) [string]

Input event file or list of event files. If the first character of the input string is '@', the rest of the string is taken to be a filename containing the ASCII file list of the events. The OBC_PACKET extension in these file are used to calculate the deadtime. IMPORTANT: The event file(s) should be the same used to extract the input lightcurve or the image.

outfile [string]

The name of the FITS output either a lightcurve or an image file. The DATASUM and CKECKSUM are updated.

minexpo (minimum exposure fraction) [real]

Set the threshold for the minimum exposure fraction for the lightcurve bin. Only bins with a fractional exposure higher than minexpo are written in the output file. Not applicable for image file input. The input value ranges between 0 and 1.

tchat (terminal chattiness) [integer]

Set terminal chattiness.

lchat (log file chattiness) [integer]

Set log file and chattiness in the log file: = 0 the log file is not written.

clobber (overwrite output file if it exists?) [yes/no]

Allows or prevents output file from being overwritten.

EXAMPLES

1- Correct the lightcurve samp.lc based on the information contained in the event files listed in the ASCII file evtlist. The output corrected lightcurve is samp_cor.lc.

             > cmadead infile=samp.lc evtfile=@evtlist outfile=samp_cor.lc 

2- Correct the image file image.img based on the information contained in the event files listed in the ASCII file evtlist. The output image is image_cor.img.

             > cmadead infile=image.img evtfile=@evtlist outfile=image_img.lc 

SEE ALSO

exopha, exovig

CATEGORY

sep98 ftools.cmadead