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PCA Digest: Recent Developments RXTE

This page contains information for observers about how to analyze PCA data, based on recommendations from the PCA instrument team. As the models of instrument response, background and other behaviors improve, this page will continue to be updated.

Two other pages are very important to learn about PCA analysis.

Table of Contents

What's New?

2011-06-09: Improvements to the PCA Effective Area (HEASoft 6.11)

The PCA team has released a new set of effective area values. These new values should provide improved agreement between individual PCUs, but with no change to the shape of the effective area curve and no change to the redistribution. The normalization change is 0.4% for all five PCUs together, and also 0.4% for PCU2 alone. For many observers, this change will be too small to notice. The PCA team recommends that users upgrade to the HEASOFT 6.11 release (or later). The report Improvements to the PCA Effective Area (HEASoft 6.11) has more details.

2009-12-12: Correction to PCABACKEST spike artifacts

The PCA team has discovered that PCABACKEST version 3.7 and earlier can produce spike-like artifacts in estimated background files. These artifacts can affect spectra and light curves, depending on the energies and techniques used. The PCA team recommends that users immediately download and use pcabackest version 3.8, available from the HEASOFT 6.8 release. Users can find a more detailed description of the issues in the Report.

2009-08-17: Improvements to the PCA Response Matrix

New PCA response matrix software and calibration database (CALDB) files are now available, which provide significant improvements to spectral analysis over the entire RXTE mission. Changes were made to both the energy-to-channel relationship and the modeling of L-escape lines. Users will need to use PCARMF version 11.7 (HEASOFT Release 6.7) and PCA CALDB dated 2009-08-17 or later. The spectral improvements include lower systematic residuals, improved chi-square values, and better consistency in spectral parameters across the mission. The best improvement will be seen by observers who download both new software and CALDB. Users who download only one, but not both, will see partial improvement. The report Improvements to the PCA Response Matrix (version 11.7) has more details.

Previous entries:

PCA Status

The overall PCA instrument is operating nominally. However, the five individual PCU detectors which make up the PCA have their own individual details, which are listed in the table below.
Status Operating Operating Operating Operating Operating
Propane Layer? No
(as of 12 May 2000)
(as of 25 Dec 2006)
Yes Yes Yes
(% of good-time)
~20% ~20% ~100% ~20% ~15%

Number of PCUs on as a Fraction of Total Good Time

Although the PCA has 5 PCUs, since nearly the beginning of the mission PCUs 4 and 5 have been regularly "rested" to avoid breakdowns. Now that other PCUs has begun to suffer the same types of problems, the fraction of observations obtained with all 5 PCUs on is lower.

In the past, when proposers have prepared their technical feasibility calculations they have assumed that all 5 PCU will be turned on. However, the average number of PCUs on per observation is 1.6. At times there are now only 1 PCU enabled. However, this setting is also driven by the science, for example observations which wish to simply measure the flux do not benefit from having more than one PCU enabled. As a percentage of total good time, the number of PCUs on is:
Number of PCUs enabled 1 PCU 2 PCUs 3 PCUs 4 PCUs 5 PCUs
Fraction of Time 50% 40% 5% 3% 2%

Important Downloads and Links

In the table below, you will find quick links to the important files you need. Start here if you're an experienced RXTE user, and you just want to update your files with a few clicks.

Description File Name Released / Updated
Bright background model
(net count rate > 40 ct/sec/PCU)
August 6, 2006
(covers full mission)
Faint background model
(net count rate < 40 ct/sec/PCU)
August 6, 2006
(covers full mission)
SAA History file
(use for all background models)
pca_saa_history.gz ~Daily
(few day lag)
(covers full mission)
SAA Prediction file
(use for quick-look when History
file is not available)
(also see README)
(30-day forecast)
(covers full mission)
Clock file
(use with faxbary for better than 70 μs timing)
tdc.dat ~Monthly
(covers full mission)
PCA Breakdown History
(use to filter breakdown events)
'breakfile' used by XTEFILT
GTI file
(also available in CALDB)
Daily (GOF)
Monthly (CALDB)
(covers full mission)

Ready Reference: Energy to
Channel Table
Cycle 8
Simulation Data
PCU On-Off
PCA Background
Epoch Boundaries
and Models

Analysis Tips

This section gives the PCA team-recommended files and settings in order to obtain the best possible analyis.
  • Background - the pcabackest recipe gives how-to information; see PCA team page for calibration reports.
    • PCABACKEST - version 3.8 - IMPORTANT BUG FIX updated December 2009 - fix for spike-like artifacts in estimated background (see report)
    • Background models - 20051128 version - updated August 2006
    • SAA History - daily version - updated daily (see above)
  • Response Matrix - the PCA response recipe gives how-to information; see PCA team page for calibration reports.
    • PCARMF - version 11.7 - updated August 2009 (significant response improvements - available in HEASOFT 6.7 and new CALDB releases)
    • XPCAARF - updated June 2011 (revised inter-PCU normalizations; report)
  • Filtering - the XTE Filter file recipe contains how-to information.
    • XTEFILT - version 1.8 - updated Dec 2008 (new capability for breakdowns)
    • "Apidlist" (used by xtefilt/fcollect) - see 'fhelp xtefilt' - updated 2002
    • Filtering expression - see 'Creating Filter Files' below - (updated Dec 2008)
    • PCU filtering - for spectra and light curves use PCUs 2-4.
    • PCU filtering - for timing use PCUs 0-4.
    • PCU0 and PCU1 data after propane loss - see 'PCU0 Background' below
  • Breakdowns - the PCA Breakdown recipe contains how-to and general information. (updated Dec 2008)
    • PCU breakdown files - updated daily - see above
    • PCU breakdown files - updated monthly - in XTE CALDB
  • Timing - the PCA team page has sections on absolute timing accuracy and timing signatures.

Discussion of PCU0 Background Models after Propane Loss

Even though the propane layer of PCU0 is now gone, observers can estimate an approximate background for it. Since FTOOLS version 5.2, XTEFILT has the required information. You may need to update your "apidlist." See the fhelp for the task. More details on PCU0 analysis and discussion of what to expect, can be found on the PCA Team's 2002 model documentation page. Note that this page was written before the release of the FTOOLS 5.2 and contains a few work-arounds that are no longer necessary.

Creating Filter Files and GTI Files for Use with Faint Models

Before running XTEFILT, you will need an updated apidlist so that some necessary new parameters (such as electron_n) can be calculated. Make sure you get the new list from the "fhelp xtefilt", save it as a text file, and use it as the appidfile when calling XTEFILT to create XTE Filter files.

Using MAKETIME on your XTE Filter files, create .gti files adding the additional constraints to your usual expression:

For Epochs 1 and 2:

  • (ELECTRON2 .LT. 0.1) .AND.

For Epoch 3 and later:

  • (ELECTRON2 .LT. 0.1) .AND.

The TIME_SINCE_BRK filter is new (Dec 2008), and assumes that you have produced a filter file with the XTEFILT '-b' option. You can also use a pre-generated GTI file instead of making a new filter file. See the PCA Breakdown recipe for more information.

These GTIs should be entered into the extractor at the GTIANDFILE prompt. See our pcabackest recipe for more details.

NOTE The CM models for Epoch 3 and later, unlike previous models, are based on blank sky observations with no screening on the 'time since saa' parameter. Tests show that the CM models work well in all parts of the orbit including shortly after SAA passages. Consequently, we no longer recommend screening on the time_since_saa parameter. The use of scripts that include this screening (i.e. REX as distributed in ftools 5.1) will eliminate a small amount of useful data, but will not affect systematics limited investigations.

High Frequency Time Signatures

Seeing something interesting at about 4kHz or 194kHz? The PCA team has identified some high frequency temporal characteristics, discussed in more detail by Keith Jahoda at his
Instrumental Timing Signatures page.
High Frequency Time Signatures

If you have a question about RXTE, please send email to one of our help desks.

This page is maintained by the RXTE GOF and was last modified on Tuesday, 04-Sep-2012 16:10:39 EDT.