Integral: three years of insight into the violent cosmos (Forwarded)

ESA News
http://www.esa.int

17 October 2005

Integral: three years of insight into the violent cosmos

Observing the cosmos, full of violent phenomena and extreme energy, has
been the task of ESA's Integral gamma-ray observatory since its launch on
17 October 2002. Three years later, the mission is going very well and has
recorded a wealth of important discoveries.

Integral is surveying the sky continuously using four instruments -- two
main gamma-ray instruments dedicated to imaging (IBIS) and spectroscopy
(SPI), an X-ray instrument (JEM-X) and an optical monitor (OMC).

These instruments are Integral's 'eyes' -- providing for the first time
simultaneous, single-satellite observations in different wavelengths of
the most energetic objects and phenomena in the Universe.

Its observations have already enormously contributed to scientific
subjects such as the births and deaths of stars in our galaxy, massive
black holes, ultra-compact objects like neutron stars and elusive but
powerful gamma-ray bursts, to name only a few.

Integral has been looking at gamma-ray sources within our own galaxy, the
'Milky Way', and outside it. The galactic centre of our galaxy is one of
Integral's prime targets. It hosts a super-massive black hole equivalent
to three million solar masses.

Integral made the first detection of the persistent but low emission of
highly energetic X-rays coming from the direction of the galactic centre.
Integral's observations, combined with simultaneous observations from
ESA's XMM-Newton X-ray observatory, suggested that we are seeing for the
first time particular X-ray emission directly from the immediate vicinity
of the super massive black hole. This is giving new insights on the nature
of such massive 'monsters'.

Integral is also keeping its promise to dig into the behaviour of
'antimatter'. When electrons meet their antimatter counterparts
('positrons'), they annihilate each other and produce a distinctive
gamma-ray emission. Integral provided the first galactic map ever of such
emission.

This sky distribution appears very smooth and almost symmetrical, centred
on the galactic centre itself with only a very weak component in the
galactic disk.

This suggests that, besides the annihilation of matter with the antimatter
produced, for instance by winds from massive stars or regions around black
holes and neutron stars, the annihilation with antimatter could also be
produced by an exotic form of 'dark matter'.

With its ability to see faint and fine details, Integral has identified 91
individual sources that count almost completely towards the diffuse
galactic background of soft (low-energy) gamma rays observed by previous
observatories.

The mission is also a gamma-ray burst detector, and has been spotting one
burst per month in its field of view. Integral recorded the closest and
faintest gamma-ray burst to date, suggesting the existence of an entire
population of sub-energetic gamma-ray bursts which have so far been
unnoticed in the Universe.

Other examples of Integral's discoveries relate to the study of 'compact
sources' in our galaxy. For instance, it discovered a new class of X-ray
binary stars, not seen by previous missions.

They are characterised by high masses, strong stellar winds, and accreting
material from the companion star leading to a 'cocoon' around the compact
source. Most of theses objects are located, as far as we could see so far,
in the 'Scutum' and 'Norma' spiral arms of our galaxy.

Also, extra-galactic observations of so-called 'active galactic nuclei',
combined with results from XMM-Newton, revealed that the super-massive
black hole housed in their internal regions is surrounded by a
doughnut-shaped gas cloud.

This is only a limited overview of Integral's achievements to date. So,
with such a brilliant performance so far, what new surprises will come
next from Integral?

Note to editors:

Initially planned to operate for 26 months after launch, INTEGRAL is now
in an extended mission phase. A further two years extension until 2008 has
recently been recommended by ESA's scientific advisory committees to be
approved by ESA's Science Programme Committee next month.

For more information:

Chris Winkler, ESA Integral Project Scientist
E-mail: christoph.winkler @ esa.int

More about...

* ESA's gamma-ray astronomy mission
http://www.esa.int/SPECIALS/Integral/index.html
* Integral factsheet
http://www.esa.int/esaSC/SEMD9G1A6BD_index_0.html

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IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEMY146Y3EE_index_1.html]
Integral, ESA's International Gamma-Ray Astrophysics Laboratory, is
gathering some of the most energetic radiation that comes from space. The
spacecraft was launched in October 2002 and is helping to solve some of
the biggest mysteries in astronomy.

Gamma rays are even more powerful than the X-rays used in medical
examinations. Fortunately, Earth's atmosphere acts as a shield to protect
us from this dangerous cosmic radiation. However this means that gamma
rays from space can only be detected by satellites.

At time of launch, Integral was the most sensitive gamma-ray observatory
ever put into space. It detects radiation from the most violent events far
away and from processes that made the Universe habitable.

Credits: ESA

[Image 2:
http://www.esa.int/esaCP/SEMY146Y3EE...html#subhead1]
This illustration describes a model for a gamma-ray burst, like the one
detected by Integral on 3 December 2003 (GRB 031203). A jet of high-energy
particles from a rapidly rotating black hole interacts with surrounding
matter.

Observations with Integral on 3 December 2003 and data on its afterglow,
collected afterwards with XMM-Newton, Chandra and the Very Large Array
telescope, show that GRB 031203 radiated only a fraction of the energy of
normal gamma-ray bursts. Like supernovae, gamma-ray bursts are thought to
be produced by the collapse of the core of a massive star.

However, while the process leading to supernovae is relatively well
understood, astronomers still do not know what happens when a core
collapses to form a black hole. The discovery of 'under-energetic'
gamma-ray bursts, like GRB 031203, should provide valuable clues as to
links between supernovae, black holes and gamma-ray bursts.

Credits: CXC/M. Weiss