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EDS Configurations: Good Xenon



General Description

The Good Xenon configurations use two Event Analyzers simultaneously to provide detailed spectral and temporal information about every event that survives background rejection. There are two pairs of Good Xenon configurations:

  1. Good_Xenon1_2s with Good_Xenon2_2s (the 1 and 2 denote the two EAs; the 2s is the readout time)

  2. Good_Xenon1_16s with Good_Xenon2_16s (again, the 1 and 2 denote the two EAs; 16s is the readout time).

Before you reduce Good Xenon data, you must combine matched pairs of files from the two EAs. The Perl script make_se will accomplish this task. The description of the data files that follows assumes the combination has been completed.

Files containing Good Xenon data are in science event format. The science data occupy the XTE_SE extension in the form of individual time-stamped binary event words, one per line, which fill the Event column. The words themselves are strings of ones and zeros, the combinations of which define the properties of each event with respect to a template of all possible properties within the configuration. This template is broken up into sections - one for the PCU ID, one for the anode ID, and one for the PHA channel. Thus, an individual event word, with its particular combination of ones and zeros, picks out one PCU ID, one anode ID and one PHA channel. The time stamps occupy the Time column.


Detailed Description

The key to understanding and manipulating your Good Xenon data lies in "decoding" the event word template. The template itself occupies the TEVTB2 keyword in the header of the XTE_SE extension and is written in DDL - the Data Descriptor Language. Its value for Good Xenon is:

(M[1]{1},S[Zero]{6},D[0:4]{3},E[0:63]{6},C[0:255]{8})
which, broken down into its parts, means:

  • (M[1]{1}... ) - Unlike other event mode configurations, each row in a Good Xenon file contains only one kind of event, namely, valid science events. Like other other event mode configurations, these science events are identified with an M-token, the value of which is M[1]{1}.

  • S[Zero]{6} -Housekeeping check. Each valid bitmask is preceded by six zeroes.

  • D[0:4]{3} - Detectors 0-4, i.e. PCUs 0-4 (DDL's : symbol indicates a range). The {3} means that three bits are used to identify the PCU: 000 identifies PCU0, 001 PCU1, and so on.

  • E[0:63]{6} - Detector element, i.e. xenon anode. The {6} means that six bits are used to identify the Xe anode: 000001 identifies X1L, 000010 X1R, and so on. Note that some software, notably sefilter, requires the binary substring to be entered as a base-ten number, e.g. 1 identifies X1L, 2 X1R, 4 X2L, 8 X2R, and so on.

  • C[0:255]{8} - PCU Channel. Good Xenon provides the full 256 channel range. The {8} means that eight bits are used to identify one of the 2**8 channels.

Note that the readout time of the configuration (2 or 16 seconds) has no influence on the structure or properties of Good Xenon data. Its role is to provide observers with two telemetry choices. Note too that running fdump on a Good Xenon file will not provide an ASCII dump of the bitmask.


Time and energy resolution

The resolution of the time stamps in Good Xenon is 1/2**20 seconds, i.e. 0.95367431640625 microsec. This is the value of the TIMEDEL keyword in the header of the XTE_SE extension. Good Xenon provides the full 256-channel pass band of the PCA.


Reduction requirements and options

Once make_se has been run on the Good_Xenon_1 and Good_Xenon_2 pairs,the resulting files are reduced as event files using seextrct. Apart from adjusting screening criteria, your primary reduction options include:

  • Selecting (by applying a bitmask):
    • PCU IDs
    • anodes, i.e. layers
    • channels
  • Binning the events into a light curve
  • Binning the events into 256-channel spectra

For complete details on working with Event mode data and GoodXenon data, see the RXTE Cookbook recipe Reduction and Analysis of PCA Event-Mode Spectra.

A further option is to convert the data from their event-word format into the more understandable, but more expansive, event file format which has explicit columns for the PCU ID etc. - similar to ASCA and ROSAT event lists. The conversion is effected, when you merge the two EAs, by running xenon2fits with the wrtparm=a option. Note that you will have to use the extractor ftool rather than seextrct to extract events. You will, however, be able to read the entire events file into xronos which cannot handle bitmasks at the moment.


Gain and offset

Gain and offset corrections are not applied by the EDS to Good Xenon data.


Return, if you like, to the PCA 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 13:45:44 EDT.