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This Legacy journal article was published in Volume 6, August 1995, and has not been updated since publication. Please use the search facility above to find regularly-updated information about this topic elsewhere on the HEASARC site.

The EXOSAT Interactive Analysis Software System

A.N. Parmar and U. Lammers
(Space Science Department of ESA, ESTEC, The Netherlands)

and L. Angelini (HEASARC)


1. Introduction

The EXOSAT Interactive Analysis, or IA, is the software that is used to access the original EXOSAT telemetry data to produce spectra, lightcurves, photon lists and images that can be read into standard analysis packages such as XSPEC, XIMAGE and XRONOS. For many potential EXOSAT users, the on-line EXOSAT databases contain suitable products, such as spectra integrated over each observation and 1-10 keV lightcurves with moderate time resolution, and the original telemetry data need never be accessed. Since this data is now available on-line from the HEASARC, we felt that it worthwhile to report on the capabilities and limitations of the IA software that is available for users with more specialized requirements.

EXOSAT had three sets of detectors, two Low-energy imaging telescopes (LE1 and LE2) normally used with channel plate detectors (CMAs), the medium energy detector array (ME) which provided good temporal and moderate spectral resolution and the gas scintillation proportional counter (GS) which provided improved spectral resolution compared to the ME, but with lower effective area. Good starting points for information on EXOSAT are White and Peacock (1988; Mem. Ital. Soc. 59, 1) and "The Best of the EXOSAT Express Parts 1 and 2", available from the HEASARC.

2. History of the IA

Following the launch of EXOSAT in 1983, the EXOSAT Observatory and a number of the groups closely involved in EXOSAT data analysis developed their own specialized analysis systems. The EXOSAT Observatory's system was developed to run on (even then) ancient HP1000 computers which used the RTE operating system. The use of a 16-bit machine and the limited capabilities of the operating system did not make for easily portable software and the legacy of this original platform remains even today. However, the IA programs contain much of the knowledge and expertise concerning the extraction of scientific information from EXOSAT data and should these programs become unusable, it is unlikely that this data would ever be fully accessible again. In 1990 SSD decided to port the IA to a number of UNIX operating systems and make the resulting software public. At about the same time, ESA (ESRIN/ISD in Frascati) transcribed all 8340 Telemetry tapes onto optical disks in order to ensure their survival for posterity. A copy of this archive was deposited with the HEASARC who have undertaken to convert it to FITS format. Recently SSD, in collaboration with the HEASARC, has prepared a new release (v 2.0) of the IA, the characteristics of which are reported here. The new release includes a number of bug fixes, new plotting capabilities, revised LE image files compliant with the OGIP standard and the capability of producing LE Photon Lists in FITS format. In addition, OSF1 and Solaris are now supported as well as the originally supported HP-UX, SUN-OS and Ultrix.

3. The EXOSAT Interactive Analysis

The EXOSAT IA is written in strict standard Fortran-77 and ANSI-C with the only exception being the indispensable use of the data type INTEGER*2. The system uses a UNIX Bourne-shell (sh) script to coordinate all software activities.

The Interactive Analysis system has five major components:

a) User Shell - OP

This provides an environment under which to analyze EXOSAT data. Its

major functions are:

* To register new users and create the required directory structure.

* To control the execution of the IA programs.

* To list available data and products.

* To Provide simple interfaces to XRONOS, XSPEC and XIMAGE

b) Telemetry Filing - FOTF

FOTF reads and transforms FOT data from either tape or disk to a form

suitable for input into the IA. FOTF has a number of functions:

* It checks for data consistency using the internal redundancy on a FOT.

* It divides the telemetry data into files, one for each telemetry stream per interval of unique spacecraft and instrument configuration and writes them onto a user area.

* It populates a directory on the user area allowing an easy overview of the filed data.

* It writes orbit and other data which is not obtained from the EXOSAT telemetry but is resident on the FOTs onto the user area.

c) The ME Interactive Analysis - MXIA2

This is the program to analyze ME data started by the command IA in the OP shell. The On board computer modes and data types supported can be found by typing ??:help in the IA.

One of the major complexities of ME data analysis is background subtraction. To make this easier a number of macros, or scripts, are available that automatically produce background subtracted spectra and lightcurves using a number of different techniques. Comparison of the results allows estimates of the systematic uncertainties to be made. The available macros can be listed within the IA by typing ??:mc. More information on a specific macro can be found by typing ??:xx, where xx is the macro name.

Another complex area is the assignment of absolute times to ME data. To the best of our knowledge, the necessary corrections are automatically applied when lightcurves are produced using the `sl' command (for [s]tore [l]ightcurve). Again, the use of the supplied standard macros is recommended. The major functions of the ME IA are:

* Decode and display the directory record created by FOTF.

* Display information on the configuration of the ME and available data streams.

* Allow selection of data by observation, data stream, time, phase and count rate level.

* Display and plot Housekeeping parameters (via XRONOS).

* Determine pointing directions during EXOSAT slew maneuvers.

* Allow the accumulation of energy spectra in SF format suitable for input to XSPEC. These can be converted to FITS using the SF2PHA FTOOL.

* Allow the accumulation of lightcurves in a format suitable for XRONOS.

* Allow arrival time correction of lightcurves to the Solar System barycenter.

* Provide a simple interface to the VIMAT program for the production of XSPEC response matrices.

* Allow listing of original packet data, spectra and lightcurves and plotting of spectra.

* Allow results to be corrected for the effects of deadtime, collimator transmission and known On-board Computer problems.

* Allow the background to be subtracted from spectra and lightcurves.

d) The LE Interactive Analysis - LXIA7

The LE IA is capable of creating images, lightcurves and photon lists. These can be corrected for the effects of spacecraft `wobble' by first creating a deblur file and for deadtime and vignetting effects. Images can be produced in the EXOSAT internal format (which can be read directly into XIMAGE) and FITS. Lightcurves are produced in a format suitable for XRONOS, while photon lists can be produced in FITS. Currently, it is not possible to correct LE arrival times to the Solar System barycenter.

One subtlety in the analysis of data from the LE is that the EXOSAT CMA detectors were sensitive to UV radiation. The PHA or sum-signal values written into FITS photon lists are a crude measure of the event energy and can be used to discriminate between UV and X-ray dominated sources.

The major functions of the LE IA are:

* Decode and display the directory record created by FOTF.

* Display information on the configuration of the LE.

* Allow selection of data by observation, time and exposure fraction.

* Allow the accumulation of lightcurves in a format suitable for XRONOS.

* Allow the accumulation of images in EXOSAT internal or FITS format.

* Allow the production of photon lists in FITS format.

* Allow the examination of the sum-signal distribution by applying standard FTOOLS to photon lists.

* Allow results to be corrected for the effects of deadtime, spacecraft `wobble' and vignetting.

e) The GS Interactive Analysis - GXIA7

The GS IA produces lightcurves in a format suitable for use by XRONOS and spectra that can be read into XSPEC. Currently, it is not possible to correct GS arrival times to the Solar System barycenter.

Background subtraction in the GS is somewhat tricky. Background spectra can either be obtained from nearby source-free intervals such as maneuvers or the standard background spectra which are provided can be used. In either case, the gain of the source and background spectra should be normalized using high-energy background lines or the Xe L-edges. The GS IA allows each of these options to be chosen as well as allowing the quality of fit to the spectral features to be viewed.

* The major functions of the GS IA are:

* Decode and display the directory record created by FOTF.

* Display information on the configuration of the GS.

* Allow selection of data by observation, time, phase and count rate level.

* Allow the accumulation of energy spectra in SF format suitable for input to XSPEC. These can be converted to FITS using the SF2PHA FTOOL.

* Allow the accumulation of lightcurves in a format suitable for XRONOS.

* Allow listing of spectra and lightcurves and plotting of spectra.

* Allow results to be corrected for the effects of deadtime, and collimator transmission.

* Allow background subtraction of spectra using gain normalized spectra.

4. Installation of the IA

The installation is as user-friendly and automated as possible, with little knowledge of UNIX required. The package configuration is performed by means of an interactive shell script and the actual building process is driven by a hierarchy of `makefiles.' The requirements for building and installing the IA are:

* Operating system either HP-UX (> = 9.01),SunOS (> = 4.1.3), Ultrix (> =4.3), OSF1 (> = 3.0), or Solaris (> = 2.3).

* Fortran-77 compiler.

* ANSI-C compiler (e.g. gcc (> 2.0)).

* The XANADU package available from legacy.gsfc.nasa.gov via anonymous ftp.

* Minimum free disk space for installation (excluding XANADU) of 25 Mb.

In the following, expressions in courier font represent machine text. Expressions in bold courier font represent commands that have to be typed in by the user. Note that the IA can be currently obtained from SSD and in the near future from the HEASARC.

- Getting the Archive

mkdir IA && cd IA

ftp astro.estec.esa.nl

...

cd pub/EXOSAT

bin

get IA.tar.Z

bye

- Unpacking the Archive

zcat IA.tar.Z | tar xovf -

This creates the IA subtree under the newly created directory `IA'.

- Making the IA

make config build

This runs first an interactive configuration script which should be self-explanatory and, subsequently, builds all necessary executables.

- Installing the IA

make install

This initiates the installation of the IA executables and run-time data/help files to a suitable place specified during the configuration. Note, that write access to the installation directory <IA_DIR> is needed and, thus, performing this action may require system administrator privileges.

- Cleaning Up

make clean

This removes all temporary files created during the building stage.

After the package has been successfully built and installed, it is ready to be used. The only remaining task is to add to the current search path for executables ($PATH), the location of the IA binaries. This is

<IA_DIR>/bin where <IA_DIR> stands for the IA installation directory specified during the configuration stage.

Although SSD cannot provide support for users of the IA, questions concerning installation can be addressed to ulammers@astro.estec.esa.nl.

5. A Typical User Session

Prior to running the IA, FOT data have to be available, either as magnetic tapes from ESRIN or disk files from the HEASARC on-line service. The default behavior of the filing program `FOTF' is to read FOT files from a special FOT disk directory that had been specified during the package configuration reading data from tape has to be explicitly enforced via a command line switch (foft -t). Once FOT data are present, the system can be invoked by typing op at the UNIX shell prompt:

unix> op

Type `?' to get a list of available commands

EEEEEEE X X OOOOO SSSSS A TTTTTTT E X X O O S S A A T E X X O O S A A T EEEEE X O O SSSSS A A T E X X O O S AAAAAAA T E X X O O S S A A T EEEEEEE X X OOOOO SSSSS A A T Interactive Analysis Software

----------------------------------------------------------

Tue Mar 16 11:36:52 METDST 1994

User name: [uwe]
FOT data area: [/users/uwe/datexo/raw] capacity used: 49 IA data area: [/users/uwe/datexo/ia] capacity used: 49 Current source: [defsrc] Instrument: [ME] --- Available sources -- defsrc ex2030

OP>

A list of available OP commands can be obtained with ?, the most important are probably DE, FT and IA. The first command is used to change the repository directory for the file created during the analysis (e.g., current source) and/or the instrument. The defaults are defsrc and ME. For example typing DE,ex2030 changes the current source to EX2030 allowing users to separate files from different sources. DE,,L1 changes the current instrument to be L1 which is telescope 1 of the LE. This should be performed before reading in an L1 FOT. The FT command executes FOTF (described above), and FT EY8000 would file a FOT called EY8000.fot onto the FOT data area listed above. The command IA starts the IA program for the current instrument. In the case of the ME, a welcome message will appear:


-----------------------------------------------------------------------
----								   ----
------- Welcome to the EXOSAT Medium-Energy Instrument Analysis -------
----								   ----
-----------------------------------------------------------------------

Type `??' to obtain a list of available commands Version 2.0

There are a number of help facilities within the ME IA. Typing ? lists the available commands, ??:sl will give information on command or macro sl etc, ??:mc will give information on the various macros available while ??:help will provide background information on the ME IA.

MXS13> ld will list information on the filed data :

Obs  Co  Start-Stop Main  Mech  F HT   Source            Workspace
No.  n      Times   Prog N 12  Cl?     Name           Parameters [4-8]

59 85  86 0134 0519 HER5 2 -A   Y 16   4U1624-49       1 20 256 256   4
60 85  86 0519 0521 HER5 2 ?A   Y  8   4U1624-49       1 20 256 256   4
61 85  86 0523 0529 HER5 2 A?   Y  8   4U1624-49       1 20 256 256   4
62 85  86 0530 0824 HER5 2 A+   Y 16   4U1624-49       1 20 256 256   4

MXS13> ob:59		
defines observation 59 to be current

MXS13> in 		
lists the current data stream

Obs  59 1985 086 01:34 to 086 05:19
Detectors AR  5 to 8      BG 0 to 0
OBC HER5/2  Type= EN  t=   .31250 s
Chans   5 to  68 [ 32 Bins]  ID= **
Sampled/HALF Saved ENV Cartridge XM
No LC Correction

The data stream can be changed with e.g. de,ti to the high time resolution data stream often present.

MXS12> dc,ti
MXS12> in

Obs  59 1985 086 01:34 to 086 05:19
Detectors BO  1 to 8      BG 0 to 0
OBC HTR3    Type= TI  t=   .00781 s
Chans   1 to 128 [  1 Bins]  ID= **
Sampled/INST Saved ENV Cartridge XM
No LC Correction

MXS13> oi

will provide detailed information about the
				     
EXOSAT and ME configurations during observation 59

POINTING

Source:   4U1624-49
S/C Pointing  RA: 246.134 [16:24:32] Dec: -49.061 [-49:03:39]
Source Pos    RA: 246.075 [16:24:18] Dec: -49.088 [-49:05:18]
S/C Start Altitude (Km)       163801.
S/C End Altitude              151397.
S/C Roll Angle [degrees]       339
Mean Y Offset (Arc min)           -.9
Mean Z Offset                     2.0
Beta Angle (degrees)              110

TIMES

Start Time 1985 Day 86 01:34:32 ( 165202472 MJ Secs) on 85/ 3/27 End Time 1985 Day 86 05:19:04 ( 165215944 MJ Secs) 1985 Day 86 1:034:033:016:728 PRT: 57802752 SHF: 165202473 1985 Day 86 5:018:056:978:466 PRT: 278396928 SHF: 165215936 OBC AND SAMPLING

Programs : HER5 HTR3 Output Buffer: 812 268 Slot Number : 0 5 Sampling Rates: Energy: 4096 QE: 128 Det ID: 4096 Time Tag: 0 Time Tag ADC1 ADC Mode CLSD Ar Xe Sum Select SUM Reset A1

etc... Now calculate the deadtime for observation 59 :
MXS13> dt:ca
* Record   6700/  6732
* T3 Cts/sec:   700.174
* Energy correction Factor:    1.1184
* QE     correction Factor:    1.0019
Accumulate a spectrum for observation 59 :
MXS13> as
* Record  21000/ 21543
and apply the deadtime correction to this spectrum :

MXS13> dt:sp
* Deadtime:   1.118
Store this spectrum as file `SPEC1'

MXS13> wb,spec1
Now go to observation 62, and select the background detectors :

MXS13> ob:62
MXS13> dc,de:bg,bg:no
MXS13> in

Obs  62 1985 086 05:30 to 086 08:24
Detectors AR  5 to 8      BG 0 to 0
OBC HER5/2  Type= EN  t=   .31250 s
Chans   5 to  68 [ 32 Bins]  ID= **
Sampled/HALF Saved ENV Cartridge XM
No LC Correction

Now determine the deadtime for observation 62 :

MXS13> dt:ca
* Record   5000/  5084
* T3 Cts/sec:   725.575
* Energy correction Factor:    1.1224
* QE     correction Factor:    1.0020
Accumulate a spectrum from the background detectors :

MXS13> as  
* Record  16000/ 16268
Apply the deadtime correction to the background spectrum :

MXS13> dt:sp
* Deadtime:   1.122
Store as file `BG1' :

MXS13> wb,bg1
Now subtract the background spectrum from the source one accumulated earlier:
MXS13> op,spec1,su,bg1

Store the result as file `FILE1' :

MXS13> wb,file1

Sum the spectrum between channels 6 and 40 :

MXS13> su,ch:6:40

* Bins 1: 18 or Chans 6: 40 Counts: 74.537 +/- .101 Cts/s

Now check that the background subtraction is good by plotting the current spectrum :

MXS13> ps

A pgplot window now appears in the currently defined device and the user is left with the PLT> prompt of the QDP package. When the user is finished plotting type:

PLT> quit

Now convert the file to SF format for input to XSPEC :

MXS13> xs,file1

This creates a file `file1.pha'. Type LS to see the product files that you have created. Now run VIMAT to create an XSPEC response file :

MXS13> vm,file1.pha
/users/uwe/datexo/ia/defsrc/spectra/file1.pha
EXOSAT ME AR H2
detector  collimatorresponse
    5           1.00
    6           1.00
    7           1.00
    8           1.00
* Making ME matrix for detector 5
* Making ME matrix for detector 6
* Making ME matrix for detector 7
* Making ME matrix for detector 8
response file: /users/uwe/datexo/ia/defsrc/spectra/file1.rsp

The user now decides to do some timing analysis by running macro `l2' to produce lightcurves between channels 6 to 40 for observations 59 and 62. Files FILE1 and FILE2 are created with 3.1 sec time resolution. See ??:l2 for a description of the calling parameters.

MXS13> ma,l2:59:62:6:40:10,file1,file2

etc... These files are in an internal EXOSAT format and can be converted for use in XRONOS by typing :

 MXS13> xl,file1
 MXS13> xl,file2
creating files file1.rbf and file2.rbf. The user now exits the ME IA and starts an XSPEC session via OP. This opens a dedicated xterm window :

 MXS12> exit
 OP> xs
When the user has completed the spectral analysis, XSPEC is exited in the usual way, the xterm disappears and the user decides to do some LE analysis :

 OP> de,,l1

EEEEEEE X X OOOOO SSSSS A TTTTTTT E X X O O S S A A T E X X O O S A A T EEEEE X O O SSSSS A A T E X X O O S AAAAAAA T E X X O O S S A A T EEEEEEE X X OOOOO SSSSS A A T Interactive Analysis Software ---------------------------------------------------------- Tue Mar 14 10:44:01 MET 1995 User name: [uwe] FOT data area: [/users/uwe/datexo/raw] capacity used: 50 IA data area: [/users/uwe/datexo/ia] capacity used: 50 Current source: [defsrc] Instrument: [L1] --- Available sources -- bigdip defsrc OP> ia

LXS17> listd

will list information on available data:

obs  d1  ut1  ut2  fw  det stng zoom pets grt test obc mode pt source id

07 342 1429-1438 3 lx cma 613 39 1 out * comb2 2 GAMMA CASS. 08 342 1442-1726 B cma 613 39 1 out * comb2 2 GAMMA CASS. 09 342 1732-1740 B cma 613 39 1 out * inactive 2 GAMMA CASS. 10 342 1747-1943 Al/P cma 613 39 1 out * comb2 2 GAMMA CASS. 11 342 1947-1956 Al/P cma 613 39 1 out * comb2 3 GAMMA CASS.

Now create a FITS photon list. This is carried out in two stages, first run program adima and then lcurv. Bold indicates user entries here.

 LXS17> adima
Image type (0=normal, 1=PDF, 2=FITS Image, 3=FITS Photon list): [3]
Enter FITS filename (6 char; w/o extension): [exoimg] fits1
Enter up to 15 observations to chain: [1] 11
Start time: [1984 342 19:47:46]
End   time: [1984 342 19:56:58]
Exposure time is    477 seconds
Deblur file name (w/o extension, <return> if none):
    GAMMA CASS.   star tracker mode: STR2
5" pitch axis rotation performed
Sum signal limits: [1,127]

 Processing    683 IM records
Processing small maps   0   0
Image accumulation completed
completed writing header Now use LCURV to complete this FITS file
Normal termination
LXS17> lcurv 
Do you want to complete the FITS file started in ADIMA? [Y]
Enter same observation numbers as in ADIMA: [1] 11
Start time: [1984 342 19:47:46]
End   time: [1984 342 19:56:58]
Enter DT bin size (8.0 secs): [8.0]

Processing 100% of    785 C2 records
* Record:   700

   GAMMA CASS.   star tracker mode: STR2
5" pitch axis rotation performed
Enter Xlo, Ylo, Xhi, Yhi for source 1: [1, 1, 1023, 1023]
Enter Xlo, Ylo, Xhi, Yhi for bckgnd 1: [-1023,-1023, 1024, 1024]
Fully overlapping boxes
Another pair of boxes? [N]
Enter ADIMA FITS file name (w/o extension): [exoimg] fits1

Processing   683 IM records
     7     7
FITS file Event extension completed

 Number of Exposure Bins =     69, Time spanned=  552.000 sec.
     FITS file Dead Time extension completed

This file can now be read into XIMAGE or SAOIMAGE, etc. for display or further processing.

6. Acknowledgments

Almost every member of the EXOSAT Observatory team contributed to the IA in some way. Particular thanks are due to R. Blissett, L. Chiappetti, T. Courviosier, P. Giommi, M. Gottwald, F. Haberl, J. Lewis, J. Osborne, L. Stella, J. Sternberg, G. Tagliaferri and N. White.

References

White, N.E. and Peacock, A. 1988, Memorie della Società Astronomica Italiana, Vol. 59, 7.

"The Best of the EXOSAT EXPRESS", vol 1-2, NASA/HEASARC publication.


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