Integral's first look at the gamma-ray Universe

Paris, 18 Dec 2002

INFO 10-2002.

ESA's gamma-ray satellite, Integral, is fully operational. Today Integral's first ground-breaking images of the high-energy Universe were presented in Paris, France. Astronomers call such initial observations 'first-light' images.

The high-energy Universe is a violent place of exploding stars and their collapsed remnants such as the ultra-compressed neutron stars and, at the most extreme, all-consuming black holes. These celestial objects create X-rays and gamma rays that are many times more powerful than the optical radiation we can see with our eyes and optical telescopes. Integral's Principal Investigators – the scientists responsible for the instruments on board - explain the crucial role that high-energy missions like Integral play in astronomy. "X-ray and gamma-ray astronomy is a pathfinder to unusual objects. At optical wavelengths, the number of stars is staggering. At X-ray and gamma-ray wavelengths, there are fewer objects, but the ones that remain are the really peculiar ones."

As a first test, Integral observed the Cygnus region of the sky, looking particularly at that enigmatic object, Cygnus X-1. Since the 1960s, we have known this object to be a constant generator of high-energy radiation. Most scientists believe that Cygnus X-1 is the site of a black hole, containing around five times the mass of our Sun and devouring a nearby star. Observing Cygnus X-1, which is relatively close by in our own Galaxy - 'only' 10 000 light years from us - is a very important step towards understanding black holes. This will also help understand the monstrous black hole - three million times the mass of our Sun - at the centre of our Galaxy.

During the initial investigations, scientists had a pleasant surprise when Integral captured its first gamma-ray burst. These extraordinary celestial explosions are unpredictable, occurring from random directions about twice a day. Their precise origin is contentious: they could be the result of massive stars collapsing in the distant Universe or alternatively the result of a collision between two neutron stars. Integral promises to provide vital clues to solving this particular celestial mystery.

To study these peculiarities, Integral carries two powerful gamma-ray instruments. It has a camera, or imager, called IBIS and a spectrometer, SPI. Spectrometers are used to measure the energy of the gamma rays received. Gamma-ray sources are often extremely variable and can fluctuate within minutes or seconds. It is therefore crucial to record data simultaneously in different wavelengths. To achieve this, Integral also carries an X-ray and an optical monitor (JEM-X and OMC). All four instruments will observe the same objects, at the same time. In this way they can capture fleeting events completely. Integral sends the data from all the instruments to the Integral Science Data Centre (ISDC) near Geneva, Switzerland, where they are processed for eventual release to the scientific community.

"We have been optimising the instruments' performance to produce the best overall science. We expect to be ready for astronomers around the world to use Integral by the end of the year," says Arvind Parmar, acting Integral Project Scientist at ESA. "These images and spectra prove that Integral can certainly do the job it was designed to do, and more", which is to unlock some of the secrets of the high-energy Universe.

Integral's primary mission will last for two years, but it is carrying enough fuel to continue for five years, all being well.

Notes to Editors

Integral was launched on board a Russian Proton rocket from the Baikonur Cosmodrome, Kazakhstan, on 17 October 2002. The satellite was placed in a tilted orbit that looped from 600 to 153 000 kilometres above the Earth and back again. Integral's own thrusters then steered the spacecraft, in a series of five manoeuvres, into its operational orbit, between 9 000 and 153 000 kilometres above the Earth.

Although Integral orbits above the Earth's atmosphere and weather, it still has 'space weather' to contend with. Space weather consists of a constant rain of tiny particles that can temporarily blind detectors designed to register gamma radiation. "The flashes last about 0.1 seconds and have to be filtered out with software," says Pietro Ubertini, IBIS Principal Investigator. JEM-X proved to be particularly susceptible to space weather and scientists had to 're-tune' it.

Cygnus X-1 is one of the brightest high-energy emitters in the sky. Relative to its parent constellation, Cygnus – the Swan, Cygnus X-1 it is located about halfway along the row of stars that mark the Swan's neck, at about 10 000 light years from Earth. Cygnus X-1 was discovered in the 1960s and is thought to be a black hole, ripping its companion star to pieces. The companion star, HDE 226868, is a blue supergiant with a surface temperature of around 31 000K. It orbits the black hole once every 5.6 days.

For more information please contact:

ESA - Communication Department
Media Relations Office
Tel: +33(0)1 53 69 7155
Fax: +33(0)1 53 69 7690

Dr Arvind Parmar, ESA, acting Integral Project Scientist
ESA – ESTEC, Noordwijk, The Netherlands
Tel: +31 71 565 4532
e-mail: Arvind.Parmar@esa.int

Dr Christoph Winkler, ESA Project Scientist
ESA - ESTEC, Noordwijk, The Netherlands
Tel: + 31(0)71 565 3591
e-mail: Christoph.Winkler@rssd.esa.int

For more information on the INTEGRAL mission and the ESA Science Programme, visit the ESA science website at: http://sci.esa.int/integral

The Integral Principal Investigators are:

Dr Jean-Pierre Roques, Co-Principal Investigator, SPI Spectrometer
Centre d'Etude Spatiale des Rayonnements (CESR), Toulouse cedex, France
Tel: + 33 561 556453
e-mail: roques@sigma-0.cesr.cnes.fr

Prof. Dr Volker Schoenfelder, Co-Principal Investigator, SPI Spectrometer
Max Planck Institut fur Extraterrestrische Physik, Garching, Germany
Tel: +49 89 30000 3578
e-mail: vos@mpe-garching.mpg.de

Dr Pietro Ubertini, Principal Investigator, IBIS Imager
Istituto di Astrofisica Spaziale, Area di Ricerca di Tor Vergata, Rome, Italy
Tel: + 39 06 49934090
e-mail: ubertini@rm.iasf.cnr.it

Dr François Lebrun, Co-Principal Investigator, IBIS Imager
Service d'Astrophysique CEA-Saclay, Gif-sur-Yvette Cedex, France
Tel: + 33 1 6908 3569
e-mail: flebrun@cea.fr

Dr Guido Di Cocco, Co-Principal Investigator, IBIS Imager
Istituto TESRE, CNR, Bologna, Italy
Tel +39 051 6398665
e-mail: dicocco@hotes1.tesre.bo.cnr.it

Dr Niels Lund, Principal Investigator, JEM-X
Danish Space Research Institute DSRI, Copenhagen OE, Denmark
Tel: + 45 35 325 716
e-mail: nl@dsri.dk

Dr Miguel Mas-Hesse, Principal Investigator,
OMC
LAEFF-INTA, Madrid, Spain
Tel: + 34 918131 196 (lab secretary:161)
e-mail: mm@laeff.esa.es

Prof. Dr Thierry Courvoisier, Principal Investigator at the Integral Science Data Centre (ISDC)
Integral Science Data Centre, Sauverny, Switzerland
Tel: + 41 22 950 9101
e-mail: Thierry.Courvoisier@obs.unige.ch

European Space Agency
http://www.esa.int/export/esaCP/index.ht ml