pcparpha HEADAS help file

NAME

pcparpha -- generates a Plucinsky etal background PHA spectrum for the ROSAT PSPC.

USAGE

pcparpha

DESCRIPTION

IMPORTANT: If you are using US Rev0 data to create PHA files, please see KNOWN BUGS below. There is a serious error condition which you must work around.

This task generates a 256-channel PHA spectrum of the particle background in the ROSAT PSPC from the parameterization of Plucinsky etal (1993 ApJ 418, 519)

The particle background spectrum of the PSPC is composed of three components (Plucinsky etal):

The Internal Component: This is present at all times when the PSPC is turned on, and is produced by charged particle events within the detector. Its spectrum shows a steep decrease between PI channels 18-40, but then flattens above channel 40. Spatially, this component exhibits a radial gradient whereby its normalization is 19% smaller at the edge of the detector (1 degree off-axis) compared to at the center.
The Aluminium Component: This component is only present when the filter wheel is open, and most arises from fluorescent Al Kalpha within the instrument housing. Its spectrum is that of an 1.5keV Al Kalpha line, broadened by the spectral resolution of the detector. This component shows not positional dependence except for the shadows produced by the window support structure.
The External Component: This component is only present when the filter wheel is open. Its spectrum is completely flat (ie constant count rate per channel). This component shows not positional dependence beyond that expected from the shadowing produced by the window support structure, and the decrease in unobscured open-window area as one moves off-axis.

As shown by Plucinsky etal, the count rate expected from all three 3 components correlate well with the Master Veto (MV) count rate.

The basic input parameters to the task are therefore the MV dataset corresponding to an observation, and user-defined information regarding the temporal & spatial parameters for which the background is to be generated. Any temporal filters to be applied (to the MV dataset) can be specified via an Good Time Interval (GTI) dataset. The spatial information can either be specified via an off-axis histogram dataset (which also contains the spatial extent of the region for which the background spectrum is to be generated), or specified via parameters. Users are also able to include/exclude any of the above components from the computation.

The task then uses the parameterizations given in Plucinsky etal (1993) to construct the requested spectrum. The rejection efficiency of the PSPC for particle background events for PI channels 18-249 is very high (99.90%) with a typical count rate of 4x10E-6 count/s/arcmin**2 (Plucinshky etal).

Only the the OGIP recognised PHA file formats described in Arnaud etal 1992 (Legacy, 2, 65) and its appendix provided in OGIP memo OGIP/92-007a are supported for both the input and output files.

WARNINGS ON USAGE

Please report any comments/problems or bugs to Ian M George (http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp).

PARAMETERS

outfil [character string]

The name of the o/p file to be written containing the derived PHA dataset. For safety, the name of the o/p file CANNOT be the same as one of the i/p files, and the task will stop if this is the case. Under unix/ultrix, an o/p filename identical to a file which already exists on disk is also considered illegal, and the task will stop. However, the existing file can be automatically removed, and the new file written if the o/p filename is preceeded by "!" at the outfil prompt.

(qintbgd = T) [boolean]

A logical flag indicating whether the INTERNAL background component of Plucinsky etal is to be included in the o/p file.

(qextbgd = T) [boolean]

A logical flag indicating whether the EXTERNAL background component of Plucinsky etal is to be included in the o/p file.

(qalbgd = T) [boolean]

A logical flag indicating whether the ALUMINUM background component of Plucinsky etal is to be included in the o/p file.

evrfil [character string]

The name of the file containing the Master Veto (MV) dataset.

(evrbin = 30) [integer]

This parameter specifies the bin size (in seconds) over which the mean MV rate is computed & used to calculate the background spectrum. This prcedure both speeds up the task, and smooths out the 'jitter' in MV measurements. The default value of evrbin=30 is suitable for most applications.

gtifil [character string]

The name of the file containing the Good Time Internal (GTI) dataset. The o/p PHA dataset will be constructed using the MV rate within the GTIs (only). Alternatively, the special value, gtifil = 'NONE', will result in the entire MV dataset being used (equivalent of a single GTI starting & ending at the times of the first & last measurement of the MV rate in the evrfil, respectively).

oahfil [character string]

This parameter is only required if qintbgd=T, and contains the name of the file containing the off-axis histogram dataset (fraction of time spent as a function of off-axis angle). The special value oahfil='NONE' will result in a single off-axis angle being prompted for via the theta parameter (below).

(theta = 0) [real]

This parameter is only required if qintbgd=T & oahfil='NONE', and contains the single off-axis angle (in arcmins) at which the user wishes the background PHA spectrum to be calculated for.

npixsou = % [pseudo-integer]

This is the number of pixels (of size specified by the pixsize parameter below) in the 'source region' for which the background PHA spectrum is to be calculated.

If an off-axis histogram dataset is specified via the: oahfil parameter, then the special value npixsou='%' can be used to indicate that the number of pixels is to be read from the NPIXSOU keyword of the off-axis histogram extension. If an integer value is entered, then this value will OVERRIDE the value read from the NPIXSOU keyword.
If an off-axis histogram dataset is NOT specified via the: oahfil parameter, an integer value must be specified.

pixsize = 0.00833 [real]

This parameter is only required if the value of the npixsou parameter is NOT '%', and specifies the length (in arcmin) of the side of a pixel.

(phaversn = '1.1.0') [character string]

The OGIP FITS format version for PHA datasets in which the o/p FITS file is to be written. The default is PHAVERS1='1.1.0' (also known as known as PHAVERSN = '1992a'), and is currently the only format allowed.

(chatter = 10) [integer]

Flag to indicate how chatty the task is at execution. A value of 10 is the default, with lower/higher values producing quieter/verbose output respectively.

(optaxisx,optaxisy)

Do not remove cover. No user serviceable parts inside.

KNOWN BUGS

IMPORTANT! US Rev0 format data (but not RDF data or German data which has been converted with GEVT2RDF) does not properly specify the size of the pixels in the Detector image. Because of this, the extractor (the program that xselect uses to make a spectrum) puts the wrong pixel size into the PHA file. The extractor will be modified to cope with this deficiency in US Rev0 data but it isn't fixed yet. So if you use US Rev0 data and you use xselect to creat a PHA (spectrum) file, you must change the DELTX and DELTY parameters to get a correct answer.

You need to change the CDELT1 and CDELT2 keywords to 2.595021e-4 times whatever the value of your WMREBIN keyword is (usually 15). You can use FKEYPRINT to find the value of WMREBIN and FPARKEY to put the new value into CDELT1 and CDELT2. If you have perl installed at your site (and you probably do since ascascreen is written in perl and if you don't, bug your sysadmin to install it) the script fixrev0pha will do these changes for you (type 'fhelp fixrev0pha' to see the help page).

We apologize for this flakiness, but it is a prime example of why we needed the RDF format in the first place.

This task should still be considered as a BETA test version. Please perform spot checks and report all potential bugs to http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp.

LOG OF SIGNIFICANT CHANGES

v2.1.0 (1994 August)

WMAP support

v2.0.0 (1994 April): Public release version
v1.0.0 (1994 Feb): Pre-release version (called PSPCBKGD)

PRIMARY AUTHOR

Ian M George

HEASARC

NASA/GFSC

http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp

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