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EDS Configurations: Event Burst Catcher



General Description

The generic Binned Burst Catcher configurations are designated with a character string beginning with CB, e.g. CE_16us_64M_0. Before describing the structure of Event Burst Catcher data, we review how the burst catching works.

Two Event Analyzers are required to catch bursts: one for the trigger, the other for the catcher. The Data Buffer in the catcher EA is divided into four equal parts, one per "Interval". If, say, the trigger is activated during Internal N, the trigger EA will discover this fact during Interval N+1 and the burst flag will be set. During Interval N+2, the flag causes the catcher EA to read into its memory the data for Interval N-1 (the oldest in the Data Buffer) while at the same time accumulating data from Interval N+2 in the appropriate quarter buffer. During the accumulation of N+3 data, the N data are read out, as are the post-onset N+1 and N+2 data. The readouts then cease, yielding a train of data comprising four quarters the second of which contains the burst onset. For more details about how Burst Catcher modes works, please consult the Technical Appendix.

Files containing Event 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 which, depending on the particular configuration, refer to things like PCU ID, PHA channel band, etc. Thus, an individual event word, with its particular combination of ones and zeros, picks out, say, one PCU ID, one PHA channel band, etc. The time stamps occupy the Time column, but are also encoded in the event word.


Detailed Description

The name of the configuration provides a summary of the properties of the corresponding data. For Event Burst Catcher data, the format

CE_ttt_ccX_l

gives

CE
- mnemonic denoting a event burst catcher mode
ttt
- the time bin size ("us" denotes microseconds)
cc
- the number of energy channels
X
- the code denoting the binning of the energy channels
l
- the lower channel boundary (usually 0)

As a special case, there are also GoodXenon1 and GoodXenon2 burst catchers.

For example, in the CE_8us_32B_0 configuration, 32 histograms with ~8-microsecond resolution are accumulated from channels 0 to 256, with the "B" channel distribution/binning scheme. For a complete list of Binned Burst Catcher configurations, see the RXTE PCA Configurations page. For more details about these configurations, please consult the Technical Appendix.

The Event Burst Catcher mode captures 33,767 events (plus time markers) each time a trigger signal is recieved. If the trigger is high-priority, the data are immedidately transferred to the spacecraft. If the trigger is low-priority, the data from the current trigger is stored and data from the previous trigger is sent to the spacecraft.

The remainder of the details of the event burst catcher are the same as the generic event mode.


Burst Trigger Modes

The Event Burst Catcher modes are triggered by a second EA running a Burst Trigger Mode. The trigger EA is synchronized with the catcher EA, so the data have the same Intervals. The ModeSpecific column in the XTE_SA extension of the trigger data file contains the times of trigger activation. A zero denotes no activation. These configurations will also trigger HEXTE.

There are two flavors of Burst Triggers: High Priority and Low Priority. The corresponding configurations have names beginning with T, e.g. or TLA_1s_10_249_1s_500_F and TLM_31us_0_249_500ms_QN, respectively. The format for the High Priority Trigger is

TLA_ttt_ll_hh_rrr_ccc_b

gives

TLA
- mnemonic denoting a high priority burst trigger mode
ttt
- the time bin size
ll
- the lower channel boundary (usually 10)
hh
- the upper channel boundary (usually 249)
rrr
- the read out time
ccc
- the count threshold (in counts/bin)
b
- the code denoting number of bits per bin

Low priority triggers are denoted TLM, THM, or TEM, for triggers based on count rate, hardness ratio, or edge, respectively.

For a complete list of Burst Trigger configurations, see the RXTE PCA Configurations page. For more details about these configurations, please consult the Technical Appendix.


Time resolution

The time resolution for Event configurations is the resolution of the time stamps. This is not necessarily the same as the number in the name of the configuration, which is an approximation. For example, in the CE_8us_32B_0 configuration, the step size is really 1/2**17 seconds, i.e. 7.6293945 microseconds. To derive this number, work out the nearest inverse power of two from the configuration name.


Energy resolution and channel boundaries

The configuration name gives the number of channel bands, but not the channel boundaries themselves, which are denoted by a code letter. To derive the channel boundaries, either look them up in the Technical Appendix, or run fdump the data file and look at the header of the Event column. The value of the TEVTB2 keyword gives the channel boundaries. The energy resolution also depends on the configuration: the bins in any spectrum you extract will be the same as the channel bands in the configuration


Reduction requirements and options

Spectra and light curves may be extracted from Event Burst Catcher mode data in much the same way as for Event mode data using the ftool seextrct. Apart from adjusting screening criteria, your primary reduction options include:

  • Selecting by applying a bitmask, in particular:
    • PCU IDs (depends on configuration - some do not have PCU ID)
    • anodes, i.e. layers (depends on configuration - some do not have anode ID)
    • channels (depends on configuration - some have only one channel)
  • Binning the events into a light curve
  • Binning the events into a spectrum (depends on configuration - some have only one channel)
For complete details on working with Event mode data, see the RXTE Cookbook recipe
Reduction and Analysis of PCA Event-Mode Spectra.


Gain and offset

Gain and offset corrections are applied by the EDS to generic Event 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 13:45:43 EDT.