Currently, the ISDC Data Centre for Astrophysics hosts support for several scientific projects (INTEGRAL, Planck, Gaia, astro-H, Polar, and CTA), but originally it was completely focused on the INTEGRAL mission, as the name ISDC, the acronym of "INTEGRAL Science Data Centre", testimonies. The main task of ISDC is still being the interface between the INTEGRAL satellite, which is a cornerstone of high-energy astrophysics in the XXI century, and the scientific community worldwide. It is located in Ecogia, Versoix, near Geneva and is attached to the Geneva Observatory, itself part of the University of Geneva. The ISDC is currently hosted in three separate buildings near to each other. The picture on the right shows the main building, the so called ``castle''. The second building is an old "barn" completely restored for the needs of the ISDC operations and the third one, the so called "pavilion'', is a new building, inaugurated in April 2002.

The tasks of the ISDC

The ISDC is responsible for the analysis and processing of INTEGRAL data, which are made directly usable by scientists. It also provides to the scientific community a reliable and tested software for the data exploitation. As gamma-ray astronomy concerns many research subjects of astrophysics, the ISDC had put a major effort in making the data and the software easily usable by a large variety of scientist, not all of which are familiar with the instrumentation used in gamma-ray observations.

The ISDC created and maintains the INTEGRAL archive accessible on the internet, which includes the original data as well as the results of the analysis, and a General Reference Catalog, which includes all the sources detected by INTEGRAL. Finally, the ISDC monitors closely the instruments in order to detect eventual problems and solve them together with the instrument teams. Scientific data are also checked in order to monitor the extremely variable X-ray sky exploiting the large field of view of the instruments.

The different entities of the INTEGRAL mission

The ISDC is part of the ground support segment. The illustration below shows the links between the different entities.

INTEGRAL ground segment and data flow

The observing proposals are submitted by the science community to the INTEGRAL Science Operation Centre (ISOC) located in Villafranca del Castillo near Madrid (Spain) The observation plan is prepared by the ISOC and transmitted to the Mission Operation Centre (MOC), which is part of the European Space Operation Centre (ESOC), and is located in Darmstadt, Germany. The MOC performs all spacecraft and instrument commanding, and provides the ISDC with the raw data from the satellite. The ISDC analyses, archives and distributes these data to the science community.

Timetable of the INTEGRAL mission

INTEGRAL was launched on October 17, 2002. Before launch, the ISDC was setting up the infrastructure necessary for the operations. Since launch, its main task is to process and archive the data and produce and exploit scientific data and results in the form of alerts, sky images, light curves and spectra.

Timetable of the ISDC operations

Before launch

All software currently used at the ISDC had to be developed and tested for the needs of the mission. To complete this task, the ISDC was working closely with the teams responsible for the development of the instruments aboard the satellite. About 100 people from many countries contributed to the ISDC. Teamwork is essential to ensure that the data analysis programs are perfectly adapted to the instruments. High-performance analysis software should determine the characteristics of cosmic sources from the signals generated by the instruments.

After launch

The launch was followed by a period of tests of the satellite and its instruments before entering the phase of scientific data production. For the ISDC, this was a very busy period. Analysis software had to be adapted to the in-orbit behavior of the instruments which is vital for the further development of the observation program, as the instrument behavior rarely corresponds exactly to expectations based on simulations and measurements on the ground.

ESA has also asked the ISDC to play a major role in the solving of possible technical problems with the instruments, and in the improvement of the working parameters. The knowledge of the instruments and software lies within the ISDC, where all the information is centralised and compared with the data. The ISDC can therefore offer a better support to the community through its help desk.

Currently, the ISDC produces continuously pre-processed data and standard analysis results. Both types of data are archived and distributed to the users. About one year after the completion of an observation, the data of this observation becomes publicly available. The quality of the data and products supplied by the ISDC is regularly checked.

Details of the operations

The ISDC receives the data from INTEGRAL in real-time and continuously. The data are sent digitally from ESOC (Darmstadt) with a transmission speed of 96 kilo-bits/second. The data are archived immediately, and at the same time formatted and sent for a quick-look analysis.

The quick-look analysis

The quick-look analysis consists of comparing the INTEGRAL data with the expected flux from known sources. In the case of large discrepancy, the ISDC informs the Operation Centre (ISOC) and the interested scientists within a few hours. The observation program can thus be modified to allow a better study of the variable source. This process is extremely important in gamma-ray astronomy, as gamma-ray sources are highly variable in time. As a matter of fact, there are observations that can be performed only when a source is in a particular state (the Target of Opportunity observations), these can be triggered also thanks to the quick look analysis performed at ISDC. A major task of the operations is spotting new transient sources in the incoming data, and pass the information to the commmunity through an astronomer's telegram in collaboration with the observation PIs.

The ISDC also calculates the location of gamma-ray bursts, and supplies this information within less than a minute to astronomers worldwide. This information is used to get observations of the gamma-ray bursts at other wavelengths. Besides the processing of the data, the ISDC constantly monitors the instruments and their parameters to ensure that they behave as planned.

Standard analysis, data archiving and distribution

Most operations of reception and pre-processing of the data are done in real-time. The operations described below do not possess this characteristic.

The analysis of the data which supply an image of the sky are completed a few weeks after the data have been sent by the satellite. This analysis is made using the ISDC resources (computers, network) and with analysis programs specially developed and set up to function automatically. This analysis provides standard results which are archived together with the data. Further analysis are performed later by ISDC scientists and staff of other institutes for specific studies.

The standard analysis provides sky images, spectra and light curves. These results are compared against what we already know of the gamma-ray sky. The last routine task accomplished by the ISDC is following the instrument calibration. Before launch, the calibrations were done with the data supplied by the instrument teams from ground based measurements. Now, we use data collected in orbit.

The ISDC Consortium

The ISDC is supported and funded by a dozen institutes in Europe and the United States. The map below shows the location of these institutes, and allows to reach their WWW site (opened in another window) through the red points.

The institutes member of the ISDC Consortium

Many institutes outside Switzerland have sent astronomers or software engineers to the ISDC. These people have spent many years at the ISDC working on the development of the software and the mission preparation. In Switzerland, the ISDC is financed by the Confederation, the "Fonds National de la Recherche Scientifique", the ESA PRODEX Program and the University of Geneva.

The Swiss and Geneva contributions are not only used to finance personnel costs, but also to take care of infrastructure and running costs.

The ISDC and Switzerland

The presence of the ISDC in Switzerland allows Swiss scientists to participate in a special way to the development of high-energy particle astrophysics, giving them a prime access to the information and data of INTEGRAL. This location near the Geneva Observatory also stimulates collaborations. The ISDC participates in the development of astronomy at a regional level by organising seminars, which given by astronomers visiting the centre.

The ISDC plays also a role in the formation of students. Being an important project, INTEGRAL offers to students the possibility to participate actively in a international project, getting experience in the constraints and advantages of international environment, as well as a knowledge of the structures and working methods used in a large project.