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Astronomical Data Analysis Software and Systems VI
ASP Conference Series, Vol. 125, 1997
Editors: Gareth Hunt and H. E. Payne

Real Time Science Displays for the Proportional Counter Array Experiment on the Rossi X-ray Timing Explorer

A. B. Giles1
Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771 E-mail:

1also Universities Space Research Association



The Rossi X-ray Timing Explorer ( RXTE) spacecraft contains a large Proportional Counter Array (PCA) experiment which produces high count rates for many X-ray sources. Telemetry from RXTE is returned via the NASA Tracking and Data Relay Satellite System (TDRSS) which provides a stream of nearly continuous real time data packets. This allows opportunity for some serious real time interpretation and decision making by the experiment controller, duty scientist, and Guest Observer (GO), if present. The GOs also have the option of arranging for the remote display of programs at their home institution. This paper briefly describes the available Science Monitoring subsystem display options.


1. Introduction

The PCA is one of three experiments on RXTE, and was developed at the Goddard Space Flight Center (GSFC). The RXTE experiment software effort was widely distributed, and the Instrument Teams (IT) were contracted to deliver much supporting code for their hardware experiment. During 1992, it was decided to use C++ for all of the software associated with the Science Operations Facility (SOF), but this decision was revised in mid-1993. At this time the Guest Observer Facility (GOF) elected to stay in line with the well established practices of the Office of Guest Investigator Programs (OGIP) and High Energy Astrophysics Science Archive Research Center (HEASARC) activities within NASA at GSFC. The SOF was committed to using C++ and continued with this approach. The SOF build deliveries were driven by the inexorable requirement to keep up with the spacecraft's aggressive schedule, and the need to support various tests and mission simulations. The GOF development was under far less pre-launch pressure. Since almost all GOF code is written in FORTRAN using FITS and FTOOLS, there could be no commonality with the SOF object-oriented C++ environment. This fundamental decision meant that the original requirement for an integrated system with extensive analysis capability in the SOF, was no longer feasible. Resources did not allow the duplication of the functionality of the analysis tools that the GOF was required to produce.

The PCA C++ code produced for the SOF was developed using Object Center® from CenterLine Software Inc. The GUI used is TAE+, which is a commercially available NASA product. Individual graphs were produced using the Athena Tools plotter widget set. Code was delivered to the following SOF subsystems: Command Generation (CG), Mission Monitoring (MM), Health and Safety (HS), and Science Monitoring (SM). In this paper we discuss only the SM subsystem contributions.

2. Design Requirements

The PCA experiment contains five similar detectors, each of which produces identical housekeeping data packets for the HS displays. These packets contain many detector parameters and some X-ray rates, but no spectral information. Most science data packets are generated by the Electronic Data System (EDS), which is provided by the Massachusetts Institute of Technology (MIT). This sophisticated data selection and compression system allows many pre-programmed data modes to be run simultaneously in the six Event Analyzers (EAs) devoted to the PCA. Extensive details on the PCA/EDS combination can be found in the RXTE NRA (1995). Further details of the RXTE spacecraft and mission can be found in Swank et al. (1994) and Giles et al. (1995). The requirements for the SM displays are summarized in Table 1, in approximate order of increasing scientific interest.

Given the practicalities following the SOF/GOF split, the PCA team chose to emphasize the following aspects in SOF displays: real time or near real time graphical displays, visual impact and clarity, multiple options within a pre-defined set of choices, limited analysis capability but export of data to external tools like IDL, and support for only a few of the many EDS modes, concentrating on Standard Modes 1 and 2. Remember that detailed analysis is not intended with this real time system. If GOs are present at the SOF during their observations and need to do higher level tasks, such as background subtraction or spectral fitting in near real time, the GOF's Fits Formatter (XFF) system can be used. A SOF copy of XFF can be run to produce temporary FITS files on an estimated 15-30 minute time frame. The precise time scale depends on the data flow from the NASA PACOR system into GSFC and ``fast'' FITS files made in this way may be very incomplete. Normally, a 24 hour period elapses before all late packets are assumed to have arrived. Once the FITS files are created, they can be studied using the GOF FTOOLS.

3. Science Monitoring Displays

The set of display programs developed to address these monitoring requirements is detailed in Table 2. These displays can all be run individually or, more commonly, selected from a main GUI interface.

The main GUI allows multiple instances of programs to be started, e.g., it is common to run four light curve options at the same time-0.125, 1, 8, and 16s temporal resolution. These displays then span 128s, 1024s, 2.28hours, and 18.2hours respectively. Standard Modes 1 (mainly temporal) and 2 (mainly spectral) are always present. These displays have too many features and options for a detailed discussion (see User Guide, Rhee 1995; Design Guide, Giles 1995). A document containing sample screens for the PCA real time SM subsystem is referenced on the WWW RXTE SOF page. New options are carefully tested before transfer to the SOF configuration controlled environment.

4. Operations

RXTE was a fixed price program that was completed within budget and on time with respect to goals set ~4 years prior to the planned launch. RXTE was launched on 30th December 1995 and has already produced a vast amount of high quality timing data on a wide variety of X-ray sources. The various PCA monitoring displays have proved very effective in supporting the mission and have allowed the sort of interactive decision making that was hoped for. The duty scientist and experiment controllers monitor the observation in progress, to try and ensure that it is proceeding as planned, and that modifications to the observing modes are not required. RXTE can also be slewed rapidly to point at new Targets Of Opportunity. The PCA instrument team has permanent access to the SOF data flow, to monitor their experiment using the same display programs. Guest observers need not be present at GSFC-they routinely monitor their observation in real time from their home institution using remote displays of the same suite of programs running in the SOF. RXTE has already made many public observations and this is expected to continue in the future. The SOF are in the process of providing a mechanism for real time public data to be seen by anyone in the world via a WWW interface to the PCA display programs.


The design of these software systems has benefited from much comment and input from my fellow scientists in the PCA Instrument Team. The coding for the PCA SOF subsystems was performed in varying degrees by Vikram Savkoor, Hwa-ja Rhee, Ramesh Ponneganti, David Hon, Aileen Barry, and Arun Simha who were all with the Hughes STX Corporation working under contract for NASA.


RXTE 1995, 1st RXTE NASA Research Announcement, January

Giles, A. B. 1995, PCA Science Monitoring, Design Concepts, Screen Functions, SOC User Interface, Version 6.1, December

Giles, A. B., Jahoda, K., Swank, J. H., & Zhang, W. 1995, Publ. Astron. Soc. Aust., 12, 219

Rhee, H. 1995, PCA Science Monitoring User's Guide, Version 4.1.1, August

Swank, J. H., et al. 1994, in NATO ASI Series C, vol. 450, The Lives of the Neutron Stars, eds. M. A. Alpar, U. Kiziloglu, & J. van Paradijs, (Dordrecht: Kluwer), 525

© Copyright 1997 Astronomical Society of the Pacific, 390 Ashton Avenue, San Francisco, California 94112, USA

Next: A Graphical Field Extension for sky
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