NAME

USAGE

DESCRIPTION

The niswbkglc task estimates a background lightcurve file that can be used to correct a the lightcurve of a NICER target observation containing source and background counts. This background file is estimated using a set of NICER background events (derived from observations of "blank" fields) based on the distribution of the KP solar activity index, the cut-off rigidity (COR_SAX) and the SUN_ANGLE appropriate to a given observation.

This task produces a background lightcurve file containing an estimate of the NICER background counts in each time bin. This background file can be subtracted from the NICER target lightcurve using standard tools.

Inputs

The required inputs to the task are

• Lightcurve file (infile). This is the target lightcurve file for which you require a background estimate. It should have an accurate GTI extension.
• Output file (outfile). This is the name of the output lightcurve file containing the background estimate in each time bin.
• Filter file (mkfile). This is the filter file which should cover the time range of the accumulated spectrum. I.e. the spectrum GTIs and filter file times should overlap.
• File with FPM Selection information (selfile). This can be either a cleaned event file with an FPMSEL extension, or the filter file.
• Range of PI values to calculate the background (pirange=30:800). This is specified as Min_PI:Max_PI, where Min_PI is the minimum NICER PI channel to include, and Max_PI the maximum NICER PI channel to include in the estimate.

CAVEAT: This tool estimates background based on the distribution of the "space weather" parameters (KP, COR_SAX and SUN_ANGLE) in each time bin. Because time bins are usually small, the distribution of these space weather values in the target file may not always match the distribution in the background events file, resulting in 0 counts in a given bin. Bins with 0 estimated background counts should be treated with caution. The user may want to linearly interpolate the estimated background using the non-zero bins, and use the interpolated values thus derived as an estimate of the background through the entire target lightcurve.

Also, please note that this task requires a filter file which has been generated by niprefilter2 version 2.0 or higher. It is possible to run nicerl2 to generate a revised filter file without disturbing your event file by running nicerl2 with the option tasks=MKF.

The task assumes you have access to NICER's Calibration Database (CALDB) in order to access various background calibration files. The NICER CALDB can be installed on a locally mounted disk, or accessed at the HEASARC over the internet.

Outputs

The outputs of the task is an output background pha file that can be loaded as a background file within XSPEC. This is a standard OGIP "type I" spectrum file.

When run to completion, niswbkglc produces an output lightcurve file as specified by the outfile parameter with the specified time binning.

PARAMETERS

infile [filename]

Input lightcurve file name for which the background lightcurve is to be estimated. If updatelc=YES, this file must be writable.

outfile [filename]

Name of output estimated background file.

mkfile [filename]

Name of the filter file (.mkf file).

selfile [filename]

Name of the file containing FPM Selection information. This should either be the cleaned event list (recommended), although the filter file can also be specified if necessary, with the limitations described above.

pirange="30:800" [string]

PI (energy bin) range to include in light curve. The default of 30:800 indicates 0.30 - 8.00 keV. Either low:high or low-high notation is allowed.

(gtifile="$INFILE[GTI]") [string]

File name[extension] containing the Good Time Interval used to create the input spectrum file. The patterns $INFILE and $OUTFILE are replaced by the infile and outfile parameters. Therefore, the default setting of "$INFILE[GTI]" will look for the GTI extension of the input file.

(auxilfile = NICER_AUXIL/30nov18targskc_enhanced.evt) [string]

Name of background event file.

(gti_min = 0).

Minimum gti duration to use, in seconds.

(selcol = INDEF) [string]

FPM Selection column name (or INDEF)

(updatepha="YES") [boolean]

If yes, then modify the input file's BACKFILE keyword to be background file output by this task.

(cleanup="YES") [boolean]

If yes, then clean up temporary files. If no, temporary files remain. This is typically for debugging.

(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 = 4 or higher will produce detailed diagnostic output; chatter = 1 prints out a basic diagnostic message. The default is to produce a brief summary on output.

(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 niswbkglc task parameters that were used to produce the output file.

EXAMPLES

Run niswbkglc for myspectrum.pha, using the spectrum's GTI, for all pre-launch operating detectors. The filter file is ni1234567890.mkf and the cleaned event file with FPM Selection information is in ni1234567890_0mpu7_cl.evt.

   niswbkglc myspectrum.pha myspectrum-bkg.pha \
     ni1234567890.mkf ni1234567890_0mpu7_cl.evt \
     myspectrum_sky.arf myspectrm.rmf 

SEE ALSO

niscorpeon

nibackgen3C50

niprefilter

niprefilter2

nicerarf

nicerrmf

nicerl2

LAST MODIFIED