National Aeronautics and Space Administration

EDS Configurations: Generic Event

• General Description
• Detailed Description
• Time resolution
• Energy resolution and channel boundaries
• Reduction requirements and options
• Gain and offset

The generic event configurations are designated with a character string beginning with E, e.g. E_1us_1M_0_1s. 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.

E_ttt_ccX_ll_rr

For example, in the E_31us_16M_50_1s configuration, events are time-stamped with 31-microsec resolution, in 16 PHA channel bands with the "M" channel distribution/binning scheme starting at channel 50, and are read out every 1 second. For a complete list of available Event mode configurations, see the RXTE PCA Configurations page. For more details about the different event mode configurations, please consult the Technical Appendix.

The configuration name does not, however, give a complete description of the data. Rather, the key to understanding your Event data lies in "decoding" the event word template. The template itself occupies the TEVTB2 keyword in the header of the XTE_SE extension. It is written in DDL - the Data Descriptor Language - and can be displayed on the screen using the ftool fkeyprint. But since the TEVTB2 keyword can be somewhat long, it is often better to look first at the neighbouring - and complimentary - TDDES2 keyword. Also written in DDL, the TDDES2 keyword describes which events have been selected by the EDS. As an example, here is the value of TDDES2 in the E_1us_1M_0_1s configuration:

D[0~4] & E[X1L^X1R^X2L^X2R^X3L^X3R] & C[0~249]

• D[0~4] - events come from detectors 0-4, i.e. PCUs 0-4 (DDL's ~ symbol denotes a range).

• E[X1L^X1R^X2L^X2R^X3L^X3R] - each event comes from only one of the the six detector elements per PCU, i.e. the six Xe anodes (DDL's ^ symbol denotes an exclusive or).

• C[0~249] - events come from channels 0-249.

Now let's look at the TEVTB2 keyword for the same E_1us_1M_0_1s configuration:

(M[1]{1},D[0:4]{3},T[0.0:0.00390625;9.5367431640625e-07]{12})^
(M[127]{8},S[One5]{5},S[FirstFlag]{1},S[SpillFlag]{1},S[Zero1]{1})^
(M[1]{8},S[LostEvents0]{8})^
(M[2]{8},S[LostEvents1]{8})^
(M[4]{8},S[Zero]{7},S[Spillage]{1})^
(M[8]{8},S[Zero]{5},S[ModeSpecific]{3})

• 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.

• T[0.0:0.00390625;9.5367431640625e-07]{12} - Timing information. The {12} means that twelve bits are used to specify the time when the event occurred. This done by picking out one interval among the 4096 into which the 0.00390625-second "time mark interval" is divided, thereby yielding the resolution of 9.5367431640625e-07 seconds. The zero at the beginning of the token is the value of the offset to be added to the time. When the original telemetry is converted on the ground to FITS, this timing information is decoded and written into the Time column.

Note that the readout time of the configuration has no influence on the structure or properties of Event mode data. Its role is to provide observers with telemetry choices. Note too that running fdump on an Event mode file will not provide an ASCII dump of the event words.

The header of the XTE_SE extension in generic Event files ends with a coda of keywords describing the status of the EDS.