The ABC of XTE: HEXTE Configurations: Archive

HEXTE Configurations: Archive

Since the Archive mode is always run, your data will include some Archive data. Below we discuss:

Packaging of Archive data
Time and energy resolution
Reduction requirements and options
Other features

Packaging of science data

Files containing Archive data are in science array format. The science data occupy the first, XTE_SA extension in various columns. Each row in the XTE_SA extension spans the rocking period. However, because no data are telemetered when a cluster rocks on and off target, the off-target rows contain 4 seconds less data than the on-target rows. So, for example, with 32 second rocking, each off-target row contains 28 seconds of good data. In the analysis, this is taken into account by the ftool hxtdead. In archive mode, the accumulation time is 16 seconds regardless of the rocking interval.

In HEXTE Archive mode science data:

Time occupies the Time column which gives the time of the start of each 16-second accumulation.
The counts themselves, that is, the NaI-only events that survive background rejection and pass through the pulse-height and pulse-shape discriminators, occupy two sets of columns containing the same counts:
1. SpecDet0, SpecDet1, SpecDet2, SpecDet3 contain pulse-height histograms for each detector in the cluster, accumulated every 16 seconds. The pulse-height histograms have 64 channels.
2. TimSerCnt, contains four time histograms, each with 1-second bins, covering four different channel ranges. The channel boundaries are contained in the columns MsLimit1, MsLimit2, MsLimit3, MsLimit4, MsLimit5.

The cluster position, encoded as a single integer, occupies the ClstrPosition column. The values it can assume are:

   1.5-degree rocking     3.0-degree rocking
                                          
     0   on-target          3   on-target  
     1   +1.5 deg           2   +3.0 deg   
     5   -1.5 deg           4   -3.0 deg

In common with other RXTE science array files, Archive mode files have two additional extensions containing good time intervals (GTI). Both are called GTI.

Time and energy resolution

SpecDet0, SpecDet1, SpecDet2, SpecDet3: The time resolution is 16 seconds. The spectra have 129 channels, binned according to the following scheme: channels 0-63 (binned by a factor of 2); channels 64-127 (binned by a factor of 4); channels 128-255 (binned by a factor of 8). Very roughly, each unbinned energy channel covers 1 keV.
TimSerCnt: The time resolution is 1 second. There are four energy bands spanning the channels 15-29, 30-61, 62-125, 126-250.

Reduction requirements and options

Since Archive mode yields science array files, saextrct is used for extracting light curves and spectra. Apart from adjusting screening criteria, your primary reduction options include:

SpecDet0, SpecDet1, SpecDet2, SpecDet3:
- Separating on-source and off-source data.
- Selecting and/or combining data from the four detectors
- Increasing the size of time bins when extracting a light curve
- Selecting a channel range when extracting a light curve
- Extracting 129-channel spectra
Note that both light curves and spectra must be corrected for deadtime using hxtdead.
TimSerCnt:
- Separating on-source and off-source data.
- Increasing the size of time bins when extracting a light curve
- Selecting a channel range when extracting a light curve
Note that to extract TimSerCnt, you must replace the 1CPIX12 keyword with a value which the extractor can understand, e.g. 0:3. Specify the channels appropriately (e.g. 0, 1, 2, or 3).

See the RXTE Cookbook recipe Reduction and Analysis of HEXTE Data for further details on working with HEXTE Archive data.

Other features

In addition to the columns described above - namely, Time, SpecDet0-SpecDet3, TimSerCnt, ClstrPosition - Archive mode files also contain the following:

IDFNo - the Instrument Data Frame Number at the end of each 16-second accumulation.
GoodCnt - the total accumulated "good" counts, i.e. the NaI-only events that survive background rejection and pass through the pulse-height and pulse-shape discriminators. For each 16-s accumulation, the value in GoodCnt equals the sum of the all the values in the SpecDet0-SpecDet3 columns and equals the sum of the all the values in the TimSerCnt column.
LiveTimeDet0-3 - HEXTE was designed to monitor dead time continuously. The LiveTimeDet0-LiveTimeDet3 columns are read by the deadtime correction tools hxtdeadpha and hxtdeadlc.

Return, if you like, to the HEXTE Issues chapter or to the Table of Contents.

The ABC of XTE is written and maintained by the RXTE GOF. Please email xtehelp@athena.gsfc.nasa.gov if you have any questions or comments. This particular page was last modified on Tuesday, 14-Sep-1999 13:45:41 EDT.