PCA Digest: Recent Developments

RXTE GOF	PCA Digest: Recent Developments	RXTE FAQ

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.

RXTE Cook Book - includes many PCA analysis recipes

PCA Instrument Team Page - contains more in-depth calibration information and published references

What's New
PCA Instrument Status
Important Downloads and Links for background estimation and timing
Ready Reference: Other Useful Calibration Info
Analysis tips and best practices
Discussion of PCU0 Background Models after Propane Loss
High Frequency Timing Signatures

What's New?

2008-12-01: New PCA Breakdown history files

Since shortly after launch, the PCA has experienced high voltage breakdowns, or arcing. During the breakdown, and a "resting" period afterward, the data from that PCU is not useful for science. The PCA team has released two new PCA breakdown history products, which allow observers to remove breakdown events automatically. The two different files allow you to filter at the filter-file stage (via a new option to the XTEFILT task) or at the extractor stage (via a new good-time interval file). The new files are available periodically from the XTE site (see downloads section), or from CALDB. See the PCA breakdown recipe for more information about breakdowns and how these files can be used to remove annoying breakdown events from your data.

2008-12-12: Redesign of PCA Digest Page

This PCA Digest page has been redesigned to summarize important information about analysis. Historical information has been moved to the 'Historical Developments' page.

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.

PCU 0 PCU 1 PCU 2 PCU 3 PCU 4

Status Operating Operating Operating Operating Operating

Propane Layer? No
(as of 12 May 2000) No
(as of 25 Dec 2006) Yes Yes Yes

On-time
(% 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) pca_bkgd_cmbrightvle_eMv20051128.mdl
pca_saa_history.gz August 6, 2006

Faint background model
(net count rate < 40 ct/sec/PCU) pca_bkgd_cmfaintl7_eMv20051128.mdl
pca_saa_history.gz August 6, 2006

SAA History file
(use for all background models) pca_saa_history.gz ~Daily
(few day lag)

SAA Prediction file
(use for quick-look when History
file is not available) pca_saa_predict.gz
(also see README) ~Daily
(30-day forecast)

Clock file
(use with faxbary for better than 70 μs timing) tdc.dat ~Monthly

PCA Breakdown History
(use to filter breakdown events) 'breakfile' used by XTEFILT
GTI file
(also available in CALDB) Daily (GOF)
Monthly (CALDB)

Ready Reference:	Energy to Channel Table	Cycle 8 Simulation Data	PCU On-Off History	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 3.6 - updated April 2008 (improved error messages)
- 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 11.1 - updated December 2007 (significant response improvements)
- XPCAARF - updated December 2007 (revised inter-PCU normalizations)
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 data - see 'PCU0 Background' below
Breakdowns - the PCA Breakdown recipe contains how-to and general information. (new 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.
- Clock correction - updated daily - see above
- Barycentering - FXBARY or BARYCORR tasks
- Timing signatures - see 'High Frequency Time Signatures' below (but also the PCA team page)

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 Craig Markwardt's 2002 model documentation page. Note that Craig's 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:

(TIME_SINCE_SAA .GT. 30.0 .OR. TIME_SINCE_SAA .LT. 0.0) .AND.
(ELECTRON2 .LT. 0.1) .AND.
(TIME_SINCE_BRK .LT. -150 .OR. TIME_SINCE_BRK .GT. 600)

For Epoch 3 and later:

(ELECTRON2 .LT. 0.1) .AND.
(TIME_SINCE_BRK .LT. -150 .OR. TIME_SINCE_BRK .GT. 600)

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 Thursday, 11-Dec-2008 20:23:34 EST.