National Aeronautics and Space Administration

A GUIDE TO THE INTERACTIVE ANALYSIS SYSTEM

Users are reminded that the IA system was implemented primarily as a facility whereby the community could analyze EXOSAT data in more detail at the Observatory. There is no question of the Observatory Team undertaking a systematic interactive analysis (in the absence of the user) of data as a service - this is the function of the automatic analysis. It is recommended that users of the system should as far as possible be familiar with general X-ray data analysis techniques, since the support provided by the Observatory Team is geared in general towards a demonstration of the facilities rather than a 'supervision' of the entire analysis. First time users are expected to require a few hours full time advice from the Duty Scientists followed by consultancy support on specific details.

Real time interactive analysis of LE data will not be supported because of the excessive time required to linearise the image.

During the system trial period, which will terminate on 15.03.85, no real time booking will be permitted, i.e. P.I.'s attending their current observation must request IA system time in advance in the normal manner (EXPRESS no. 7, p. 43). Only one 'observer' will be allowed access to the system at any one time a although one observer means in practice one or two 'bodies'. From 15.03.85 to 31.03.85 the Observatory Team require 100% access to the computer system for configuration, coordination of final updates and testing and documentation such that a full service will be provided from 01.04.85.

Throughout the night period (23.00-08.00) no support of the IA system is in principle available, although the Observatory Controller will be able to offer some advice, consistent with the real time DCR operations having priority at all times.

Note that the software comprising the IA system is not an Observatory product, but rather a means of production and as such is not available for distribution outside the Observatory.

A description is given of the facilities that are supported, or will shortly be supported by the ME Interactive Analysis System. The two basic end products of the ME interactive analysis are spectral and rates files. These are used by a series of analysis programs, common to all the instruments, for spectral fitting, period searching, plotting etc.

Data from the following OBC modes can be analysed with the system: HER2, HER3, HER4, HER5, HER6, HTR3, PULS, PLS2, DIR2. Note that for the pulsar programs only spectral analysis can be carried out at present and for DIR2 only a very simple analysis is possible.

a) Spectra

The data used to create a spectral file can be selected in the following ways:

1 - Argon or Xenon data
2 - Particular Detectors
3 - Time, phase or count level windows

Background subtraction can be carried out using:
1 - Slew data
2 - Array swap data, corrected for offset
3 - Standard CCF spectra
4 - Leicester University background correlations

The detector gains are stored on the spectral file at the time of creation so that the effects of detector gain drifts and pre-amplifier gain setting changes are 'hidden' from the user. In addition, deadtime correction factors can be measured or calculated and applied to the spectra. Once a spectral file has been produced it can be plotted or used as an input to the spectral fitting program.

b) Light Curves

Light curve or 'rates' files can be produced with the following options:

1 - Argon or Xenon
2 - Integration interval
3 - Energy channels (or bins)
4 - Method of background subtraction (as for spectra)

In addition, the difference in intrinsic background counting rates can be corrected for using either array swap or slew data or standard background files. The file can be deadtime corrected and for some OBC modes the deadtime correction factors can be a function of time. The times stored in a rates file can be corrected to heliocentric times; note that Madrid is assumed to be at the centre of the world and the Sun at the solar system barycentre.

The rates files can be used as inputs to the following programs:

1 - Fourier Analysis
2 - Folding Analysis
3 - 'Publication Quality' Plotting
4 - Interactive Timing analysis facility

c) Other Facilities

Other important facilities supported by the ME Interactive Analysis include:

1) Directory listings - Listings of times, OBC modes pointings of all the observations on a FOT etc.
2) Observation Information - More detailed listing for a selected observation
3) HK Analysis - Plots and listings of any spacecraft or experiment HK parameters
4) Macros - Commands can be executed from a file. Parameters can be set at execution time allowing the use of standard macros
5) Help files - On-line documentation of each command

d) Future Improvements

The ME Interactive Analysis was designed to be used by a small number of scientists each of whom would be very familiar with all aspects of the operation of - the ME, the OBC, the HP computers and the OP analysis environment. As many of the astronomers coming to use the interactive analysis will not be familiar with these, much work is currently underway to improve the help files and level of documentation. In addition, analysis of high time resolution data is very time consuming mainly because of the low CPU power of the HP computers. A link to the ESOC Fujitsu main-frame computer has been established and it is expected that many of the CPU intensive processes will be transferred from the HP's to the Fujitsu

2. The LE Interactive Analysis System

The LE Interactive Analysis System consists of more than 10 programs to enable users to perform all the basic operations needed for the detailed analysis of CMA data.

The following is a list of the main options offered by the system:

Accumulate images
Deblur images
Accumulate sum signal histograms
Calculate efficiency correction (see p. 27 for further details)
Accumulate rate files^*
Rotate images
Overlay images
Automatic source detection
Source centroid
Signal to noise ratio optimisation
Source intensity estimation and significance of detection
Hot spot removal
Gaussian smoothing
Image contouring
Pixel <--> celestial coordinates conversion
Count rate <-->flux conversion

Several interactive programs suitable for the control of colour display devices are also available.

Documentation describing the LE interactive system is currently being written and will be available at the Observatory in the near future. A two-level help file and some documentation macros are already available on the HP4 computer system at ESOC.

4. The GSPC Interactive Analysis System

Facilities available:

1. - Accumulate spectra for HEBL2 data
   HEBL4
   DIRECT (old)

2. - Accumulate rate buffers for HEBL2, HEBL4, HK data.

3. - Background subtract spectral buffers and determination of detector gain.

1. Spectral Fitting - One or two detectors up to a maximum of 256 channels. Detectors that are currently supported are GSPC, ME and all CMA filters (the latter are counted as one detector).
2. FFT - a 4096 point fast Fourier transform can be applied to the rates buffers generated by the various IA programs. For data sets longer than 4096 points the FFT's are summed together.
3. Folding - An unlimited amount of data can be folded over 75 trial periods and a plot of as a function of period obtained together with a plot of the light curve of the period with the best .
   
4. Light curves - a general purpose folding (at a single period) and light curve program will data for three detectors at once.
   
5. Timing analysis interactive system (currently in preparation and testing) common to all instruments with the following objectives:
   
   1. - 'chain' the data (bad data, fill in gaps with simulated data etc. and eliminate long term trends).
   2. - test the hypothesis of constancy by various statistical tests (, % variability) and determination of the source statistical moments.
   3. - search for flares/bursts (down to msec).
   4. - search for periodicities and determination of folded light curves.
   5. - phase fitting for pulsating sources.
   6. - characterise aperiodic variability via auto-correlation function techniques.
   7. - investigate amount of variability as a function of energy and spectral changes.
   8. - correlate data from different energy bands or experiments via cross correlation function techniques.