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12\18 ESA - Integral's first look at the gamma-ray Universe
Part 1 of 2

Paris, 18 December 2002
Information Note
Nø 10-2002

Integral's first look at the gamma-ray Universe
===============================================

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.

(continued)

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