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From: Dan Dubrick
To: All
Date: 2003-06-16 00:39:00
Subject: 6\11 ESA's XMM-Newton 1st measurement of a dead star's magnetism

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Paris, 11 June 2003
Press Release
Nx 38-2003

ESA's XMM-Newton makes the first measurement of a dead star's
magnetism

Using the superior sensitivity of ESA's X-ray observatory,
XMM-Newton, a team of European astronomers has made the first direct
measurement of a neutron  star's magnetic field.  The results provide
deep insights into the extreme physics of neutron stars and reveal a
new mystery yet to be solved about the end of this star's life.

A neutron star is very dense celestial object that usually has
something like the mass of our Sun packed into a tiny sphere only
20-30 km across. It is the product of a stellar explosion, known as a
supernova, in which most of the star is blasted into space, but its
collapsed heart remains in the form of a super-dense, hot ball of
neutrons that spins at a incredible rate.

Despite being a familiar class of object, individual neutron stars
themselves remain mysterious. Neutron stars are extremely hot when
they are born, but cool down very rapidly. Therefore, only few of
them emit highly energetic radiation, such as X-rays. This is why
they are traditionally studied via their radio emissions, which are
less energetic than X-rays and which usually appear to pulse on and
off. Therefore, the few neutron stars which are hot enough to emit
X-rays can be seen by X-ray telescopes, such as ESA's XMM-Newton.

One such neutron star is 1E1207.4-5209. Using the longest ever
XMM-Newton observation of a galactic source (72 hours), Professor
Giovanni Bignami of the Centre d'Etude Spatiale des Rayonnements
(CESR) and his team have directly measured the strength of its
magnetic field. This makes it the first ever isolated neutron star
where this could be achieved. All previous values of neutron star
magnetic fields could only be estimated indirectly. This is done by
theoretical assumptions based on models that describe the
gravitational collapse of massive stars, like those which lead to the
formation of neutron stars. A second indirect method is to estimate
the magnetic field by studying how the neutron star's rotation slows
down, using radio astronomy data.

In the case of 1E1207.4-5209, this direct measurement using
XMM-Newton reveals that the neutron star's magnetic field is 30 times
weaker than predictions based on the indirect methods.

How can this be explained? Astronomers can measure the rate at which
individual neutron stars decelerate. They have always assumed that
'friction' between its magnetic field and its surroundings was the
cause. In this case, the only conclusion is that something else is
pulling on the neutron star, but what? We can speculate that it may
be a small disc of supernova debris surrounding the neutron star,
creating an additional drag factor.

The result raises the question of whether 1E1207.4-5209 is unique
among neutron stars, or it is the first of its kind. The astronomers
hope to target other neutron stars with XMM-Newton to find out.

Note to editors

X-rays emitted by a neutron star like 1E1207.4-5209, have to pass
through the neutron star's magnetic field before escaping into
space.  En route, particles in the star's magnetic field can steal
some of the outgoing X-rays, imparting on their spectrum tell-tale
marks, known as 'cyclotron resonance absorption lines'.  It is this
fingerprint that allowed Prof. Bignami and his team to measure the
strength of the neutron star's magnetic field.

These results are being published in this week's issue of Nature.

For more information, please contact:
ESA Communication Department
Media Relations Office
Paris, France
Tel: +33 (0)15369 7155
Fax: +33 (0)15369 7690

Prof. Giovanni Bignami
Director of Centre d'Etude Spatiale des Rayonnements (CESR)
Tel: +33 561 556666
Email: bignami{at}CESR.fr

Dr Fred Jansen - ESA
XMM-Newton Project Scientist
Tel: +31 71 565 4426
Email: fjansen{at}rssd.esa.int 

For more information about XMM-Newton and the ESA Science Programme,
visit:
http://sci.esa.int

For more information about the ESA visit:
http://www.esa.int

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