This Guide is intended to do two things. The first is to show you how to get RXTE data. The second is to explain the essential properties of the files and directories in an RXTE dataset. In particular:
This Getting Started Guide does not, however, explain how to reduce RXTE data - that's covered by the materials on the Data Reduction and Analysis page. The analysis of spectra and light curves are discussed in the xspec and xronos user guides, respectively.
2. Getting RXTE Data
Both proprietary data (for PIs) and public data can be retrieved
via the Internet:
3. The RXTE Directory Structure
For the sake of simplicity and ease of use, RXTE data files are arranged in a hierarchical set of directories. The top-level directory is simply FD for FITS Database; next depends on whether the data are AO1 or later. For AO1, there is simply an AO1 directory, and then a proposal level directory. For later tapes, there is a set of directories, one of which is named after the AO and contains the proposal directory while the others contain calibration, clock, orbit, and other files. Under the proposal level directory are the individual observations, while the final level contains directories for each of the Subsystems (PCA, ACS etc.). These directory levels and their nomenclature are described in more detail below.
An important feature of the directory structure is the existence at each level of index files which refer to the contents of the directories at the next level down. These index files enable the XDF data browser to find out the contents of the entire directory tree without having to examine every file, sparing the user from this task. In fact, thanks to XDF and the index files, it's possible to browse and reduce RXTE data without directly encountering the directory hierarchy.
3.1 Top Level
The FD directory contains the directories:
3.2 Proposal Level
The proposal number, prefixed with P, is used for the name of the top of your data directory. It is assigned by the GOF when the proposals received and stays the same throughout the mission.
3.3 Observation IDs
Reflecting the fact that a single proposal may contain several targets and several pointings, the second directory level is devoted to single observations, where "observation" refers to a temporally contiguous collection of data from a single pointing. The format for the second-level directory names (also known as ObsIds) is as follows:
A Slew before observation Z Slew after observation S Scan observation R Raster grid observation G,C,D ObsIDs that may contain data gaps 0-9 Segments of a long observation (i.e., > 8 hours) b-r (reserved for) Real-time configuration changes
When not present, it indicates a regular pointed observation (< 8 hours) or the last segment of a long observation.
3.4 Spacecraft Subsystems
Each ObsID directory contains a set of 15 subdirectories, each containing data files derived from a single spacecraft Subsystem. The typical user will not need to know about most of them, but a complete listing is as follows:
ace - Attitude Control Electronics & star trackers
* If the top level Cal, Clock, and OrbitEphem directories exist, then these subsystems simply contain links to those files. The links exist so you can find the appropriate files using the index files via XDF. If those directories do not exist, then the files themselves should reside in each subsytem, so there may be many duplicate files in different ObsIds.
Though they represent the lowest rung in the directory hierarchy, the Subsystem directories do not necessarily contain files of one type. In most cases, a further division is made based on Application, the term used for a distinct source of telemetry.
Note that the ASM is not included.
4. What you Need to Know about RXTE Data Files
Each Subsystem can be thought of as a set of several distinct sources of telemetry (there are six PCA Event Analyzers, for example). These telemetry sources are known as Applications and are designated by AppIds (Application IDs). In all, there are 255 possible AppIds, and the telemetry packets they produce end up in corresponding RXTE data files after conversion to FITS on the ground.
The content of the telemetry packets from the three scientific Subsystems, ASM, HEXTE and PCA, can be arranged in different ways to maximize the science return within the overall telemetry budget. This amounts to choosing an observing mode and setting the adjustable parameters which define the mode. The combination of mode and mode parameters is known as the configuration. This is an important concept, for only data from the same AppId with the same configuration have a truly homogeneous format and can be reduced together in the same way.
RXTE has hundreds of possible configurations - and the flexibility to add new ones - but the data you get on your tape or Internet download will have only those configurations chosen for that particular observation.
4.3 Design of RXTE Data Files
The structure of the RXTE data files - FITS data tables, to be more exact - follows these design principles:
4.4 XTE Filter File:For each ObsId, the stdprod directory should contain an XTE filter file, named FP_xxxxxxx-yyyyyyy.xfl (where xxxxxxx and yyyyyyy are the start and stop time in hexidecimal mission elapsed seconds.) This filter file incorporates much of the housekeeping data from other subsystems and is intended for creating good time intervals based on those data. Checking, and remaking if necessary, this file is one of the first steps to data analysis. (See recipe.) Make sure it includes everything you will need (by plotting the columns ELV, OFFSET, PCUn_ON, BKGD_THETA, BKGD_PHI, NUM_PCU_ON, TIME_SINCE_SAA, and ELECTRONn at minimum) before you delete any housekeeping data.
4.5 Which Files Can I Delete to Save Disk Space?
For completeness and to avoid having to redistribute data, your RXTE data tape contains all the satellite telemetry, only parts of which are essential for data analysis. Here we list again the directories corresponding to the satellite subsystems, but this time with recommendations about which to keep on disk.
Please note that for most observations the PCA contributes the most telemetry: deleting the non-science subsystem directories doesn't always save a lot of space. If you still can't fit all your data onto your disk, please consider the following:
5. How to Use XDF to Browse your Files
XDF (XTE Data Finder) is a tool with a graphical user interface (GUI) to make the task of browsing the hierarchical directory structure much easier. Its end-product is a list of filenames corresponding to the data you want to analyze, as chosen by target name, time of observation, instrument and configuration.
To start XDF, type xdf at your system prompt. A window will appear on the screen divided in boxes with accompanying buttons. In broad terms, you start at the top of the window and work downwards, gradually narrowing your data selection criteria by filling the boxes until you produce the file list which appears in the box at the bottom. In more detail:
Next, use the mouse to activate the Make ObsList button on the top row. This fills the Observations box with one-line summaries of the ObsIds in the top level directory. For each ObsId, the directory name, target name, and time range are listed. At this point you can choose a particular target or time range, though for most GOs this option is not needed.
You select ObsIds themselves by clicking on them with the mouse or by pushing the All button.
The next step is to choose Subsystems from the Subsystems box by clicking on the names of the ones you're interested in.
To see the AppIds/ Configurations of your chosen Subsystem, push the Make AppIdConfigList button on the top row. Select the Appid/Configurations you're interested in from the AppIds/Configurations window.
Finally, when you've completed your choice of AppIds, push the Make FileList button on the top row. The list of corresponding files will appear in the box at the bottom of the screen: if you want to save it, push the Save FileList button on the top row to write out the list to an ASCII file called whatever you put into the File Name window. If no name is specified, it will be called "fits_files.xdf".
6. How to Install all the Necessary Software
Software for RXTE data analysis is available in the HEASoft package, a unified release of the HEASARC's FTOOLS and Xanadu software. Installation instructions are included on the HEASoft Web page.
If you have a question about RXTE, please send email to one of our help desks.