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Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
The INTEGRAL Science Data Centre
Roland Walter, Alain Aubord, Paul Bartholdi, Jurek Borkowski, Pierre
Bratschi, Tomaso Contessi, Thierry Courvoisier, Davide Cremonesi,
Pierre Dubath, Donnald Jennings, Peter Kretschmar, Tim Lock,
St’ephane Paltani, Reiner Rohlfs and Julian Sternberg 1
INTEGRAL Science Data Centre, Chemin d' ’
Ecogia 16, CH--1290
Versoix, Switzerland
Abstract. INTEGRAL is a gamma­ray observatory mission of the Eu­
ropean Space Agency to be launched in 2001. The INTEGRAL Science
Data Centre, implemented by a consortium of scientific institutions, is
the part of the ground segment which deals with the interface between
the scientific community and the INTEGRAL data.
1. The INTEGRAL Mission
The International Gamma­Ray Astrophysics Laboratory is a ``medium mission''
of the scientific programme of the European Space Agency (ESA) to be launched
in 2001. It was selected to provide the astronomical community with a gamma
ray observatory capable of the best possible spectral and angular resolution in
order to extend, in the early years of next century, the set of astronomical tools
covering the electromagnetic spectrum well into the di#cult gamma ray domain.
INTEGRAL will provide both excellent (in terms of gamma ray astronomy)
spectral and imaging resolution. The three high energy detectors (the imager
IBIS, the spectrometer SPI and the X­ray monitor JEM­X) all use coded mask
technology. INTEGRAL will therefore have an angular resolution of # 13'. The
precision of location of a bright point source will be about one arc minute. The
spectral resolution will be 2 keV at 500 keV. This will allow astronomers to
measure the profiles of gamma ray lines and to measure Doppler shifts within
the galaxy. An optical monitoring camera completes the scientific payload.
Gamma ray astronomy is now one of the tools necessary for the under­
standing of a wide range of cosmic phenomena, from the study of the interstellar
medium to that of active galactic nuclei. It is therefore important to open the
observing program to astronomers in the whole community and not to restrict
this access to those teams that build the instruments. This is not only necessary
for the community in general, but it also ensures that the instruments are used
to study the most relevant problems and thus increases the scientific output
1 Astrophysics Division, Space Science Department of ESA, ESTEC, 2200 AG Noordwijk, The
Netherlands
356

The INTEGRAL Science Data Centre 357
of the mission. INTEGRAL was therefore conceived from the beginning as an
observatory mission.
2. The INTEGRAL Science Data Centre
A gamma ray mission open to the astronomical community at large requires
that the data will be calibrated and prepared so as to be understood by non­
specialists. This has led to the concept of the INTEGRAL Science Data Centre
(ISDC). This centre is the interface between the INTEGRAL data and the users'
community. The ISDC is provided by the scientific community (the ISDC con­
sortium). It is hosted by the Observatory of Geneva and started its activities in
1996.
Gamma­ray instruments are complex and the data reduction and calibration
rest on a detailed knowledge of the instruments. The INTEGRAL data reduction
will therefore be based on instrument specific software modules written by the
teams developing and building the instruments.
The main ISDC responsibilities are (a) to receive the telemetry in real
time from the Mission Operation Centre, (b) detect gamma­ray bursts within
seconds and alert the community, (c) monitor in near real time the health of
the scientific instruments and investigate solutions with the instrument teams to
resolve problems, (d) perform a quick­look analysis of the data within 10 hours to
detect unexpected features and events (TOO), (e) convert the raw data products
into physical units, (f) taking into account the instrument characteristics, (g)
deduce source properties (images, spectra, light curves) from the observed data,
(h) archive the final data product, (i) distribute data and some software and
support the users.
3. The ISDC Software System
The ISDC software system is made of data structures, analysis executables,
pipelines and applications.
Data structures are tables and multidimensional arrays stored in FITS files.
A typical INTEGRAL observation will be split into a few hundred short (20
minutes) pointings and slews. Each pointing will result in
. 10 5 to 10 6 events and several images for the high energy instruments
. 600 images for the optical camera
. 200 housekeeping records per instrument
. auxiliary data (attitude, orbit, timing, planning, radiation monitoring
data).
The data structures, raw to processed, that correspond to a pointing will be
grouped together. All data corresponding to an observation will form a group
of about 5000 data structures for the high energy instruments and 10 5 data
structures in total. All those data structures will be grouped in a hierarchy that

358 Walter et al.
Obs. Planning
GRB Handling
Off­line Analysis
Standard Analysis
& Responses
Inst. Calibrations
Raw Data Products
Data Products
Performance
Catalogues
Housekeeping Data
Performance Monit.
Packets
Operation Status
Monitoring
Analysis
Quick Look
MOC
Auxiliary Data
Ground Calibrations
IOS Simulator
Pre­processing
On­line,
near real­time operations
Alert
Handling
Calibration Deriv.
Response Deriv.
Data Receipt
Observation Simulat.
is described in the data themselves. The data and their hierarchy are available
through the ISDC Data Access Layer (see Jennings et al. this proceedings).
In addition to the standard groups created for the proposed observations, any
group of pointings can be created for archival studies.
Analysis executables are C or F90 programs reading their inputs from and
writing their outputs to the FITS files and reading their parameters from IRAF
parameter files. The analysis executables are compatible with the FTOOLS
standards, with some extensions. Analysis executables are standalone and do
not require any other software to run.
Analysis pipelines link analysis executables together through flow control
instructions. The parameters of each executable are defined at the pipeline level
from pipeline parameters, data or database queries. Data structures are not
modified at the pipeline level but always through analysis executables. The
current baseline for pipeline scheduling is to use the OPUS system developed
for the HST. The data access layer supports data storage in shared memory to
accelerate data transmission when necessary.
Analysis applications are written to support interactive analysis of the data
as well as automatic display of the data. Interactive applications call analysis

The INTEGRAL Science Data Centre 359
executables for data manipulation and use native functions of the environment
to generate displays and interact with the users. The object oriented frame­
work ROOT developed at CERN is currently under study for writing analysis
applications.
4. Development Phases
After a phase of requirement definition, system libraries development and inter­
face specification, the architecture of the ISDC system is being built. Several
subsystems will be under development starting early in 1998 and will be inte­
grated and system tested during 1999. Overall tests involving the full ground
segment will be conducted during the year 2000.
Additional information on the di#erent elements of the ISDC can be found
on the World Wide Web pages of the ISDC (http://obswww.unige.ch/isdc/).