X-ray shout echoing through space (Forwarded)

ESA News
http://www.esa.int

27 January 2004

X-ray shout echoing through space

ESA's X-ray observatory, XMM-Newton, has imaged a spectacular set of rings which
appear to expand, with a speed a thousand times faster than that of light,
around the point in the sky where a powerful gamma-ray explosion took place in
early December. This is the first time that such a fascinating event, called an
'echo', has been seen in X-ray wavelengths.

This echo forms when the powerful radiation of a gamma-ray burst, coming from
far away, crosses a slab of dust in our Galaxy and is scattered by it, like the
beam of a lighthouse in clouds. Using the expanding rings to precisely pin-point
the location of this dust, astronomers can identify places where new stars and
planets are likely to form.

On 3 December 2003 ESA's observatory, Integral, detected a burst of gamma rays,
lasting about 30 seconds, from the direction of a distant galaxy. Within minutes
of the detection, thanks to a sophisticated alert network, many observatories
around the world were pointing their instruments at this mysterious source in
the sky, named GRB 031203, in the attempt to decipher its nature. Also ESA's
X-ray observatory, XMM-Newton, joined the hunt and observed the source in
detail, using its on-board European Photon Imaging Camera (EPIC).

The fading X-ray emission from GRB 031203 -- called the 'afterglow' -- is
clearly seen in XMM-Newton's images. But much more stunning are the two rings,
centred on the afterglow, which appear to expand thousand times faster than the
speed of light. Dr. Simon Vaughan, of the University of Leicester, United
Kingdom, leads an international team of scientists studying GRB 031203. He
explains that these rings are what astronomers call an 'echo'. They form when
the X-rays from the distant gamma-ray burst shine on a layer of dust in our own
Galaxy. "The dust scatters some of the X-rays, causing XMM-Newton to observe
these rings, much in the same way as fog scatters the light from a car's
headlights," said Vaughan.

Although the afterglow is the brightest feature seen in XMM-Newton's images, the
expanding echo is much more spectacular. "It is like a shout in a cathedral,"
Vaughan said. "The shout of the gamma-ray burst is louder, but the Galactic
reverberation, seen as the rings, is much more beautiful." The rings seem to
expand because the X-rays scattered by dust farther from the direction of GRB
031203 take longer to reach us than those hitting the dust closer to the line of
sight. However, nothing can move faster than light. "This is precisely what we
expect because of the finite speed of light," said Vaughan. "The rate of
expansion that we see is just a visual effect." He and his colleagues explain
that we see two rings because there are two thin sheets of dust between the
source of the gamma-ray burst and Earth, one closer to us creating the wider
ring and one further away where the smaller ring is formed.

Since they know precisely at what speed the X-ray light travels in space, the
team in Leicester have determined accurately the distance to the dust sheets by
measuring the size of the expanding rings. The nearest dust sheet is located
2900 light years away and is probably part of the Gum nebula, a bubble of hot
gas resulting from many supernova explosions. The other dust layer is about 4500
light years away. Understanding how dust is distributed in our Galaxy is
important because dust favours the collapse of cool gas clouds, which can then
form stars and planets. Knowing where dust is located helps astronomers to
determine where star and planet formation is likely to occur.

Expanding X-ray dust scattering rings, such as those around GRB 031203, have
never been seen before. Slower-moving rings, caused by a similar effect, have
been seen in visible light around a very few exploding stars, mostly supernovae.

The expanding rings also provide much needed information on the gamma-ray burst
itself. Gamma-ray bursts are the most powerful explosive events in the Universe,
but astronomers are still trying to understand the mystery that surrounds their
origin. Some occur with the supernova explosion of a massive star when it has
used up all of its fuel, although only stars which have lost their outer layers
and which collapse to make a black hole seem able to make a gamma-ray burst. The
delayed X-rays from the echo of GRB 031203 are very useful because they tell
astronomers how bright the burst was in the X-ray spectrum when it went off on 3
December. The only direct data available from that moment are those obtained by
ESA's Integral observatory in the gamma-ray range. "XMM-Newton's measurements
are thus crucial to better understand the nature of the burst," said Dr. Fred
Jansen, XMM-Newton's project scientist. "The more details we gather of the
burst, the more we can learn on how black holes are made."

Today, ESA's Integral and XMM-Newton observatories provide astronomers with
their most powerful facilities for studying gamma-ray bursts. In 2004 a new
gamma-ray satellite, called 'Swift', will be launched as part of a collaboration
between the USA, United Kingdom and Italy.

Swift will add to the flotilla of satellites providing fast and accurate
locations of gamma-ray bursts on the sky, which can then be followed with
XMM-Newton. This will provide even more opportunities for new discoveries in
this cutting-edge field.

Notes to editors

A scientific paper describing this discovery by Dr. Simon Vaughan and his
collaborators has been accepted for publication in "The Astrophysical Journal"
(see http://arxiv.org/abs/astro-ph/0312603).

The other members in Vaughan's team are R. Willingale, P. O'Brien, J. Osborne,
A. Levan, M. Watson and J. Tedds from the University of Leicester, United
Kingdom; J. Reeves from NASA's Goddard Space Flight Center in Greenbelt, USA; D.
Watson from the Neils Bohr Institute for Astronomy in Copenhagen, Denmark; M.
Santos-Lleo, P. Rodriguez-Pascual and N. Schartel from ESA's XMM-Newton Science
Operations Centre in Villafranca, Spain.

More about XMM-Newton

XMM-Newton can detect more X-ray sources than any previous satellite and is
helping to solve many cosmic mysteries of the violent Universe, from black holes
to the formation of galaxies. It was launched on 10 December 1999, using an
Ariane-5 rocket from French Guiana. It is expected to return data for a decade.
XMM-Newton's high-tech design uses over 170 wafer-thin cylindrical mirrors
spread over three telescopes. Its orbit takes it almost a third of the way to
the Moon, so that astronomers can enjoy long, uninterrupted views of celestial
objects.

For further details please contact:

Dr. Simon Vaughan
Department of Physics and Astronomy
University of Leicester
Tel: +44 116 252-3510
E-mail:

Dr. Richard Willingale
Department of Physics and Astronomy
University of Leicester
Tel: +44 116 252-3556
E-mail:

Dr. Fred Jansen
XMM-Newton Project Scientist
European Space Agency
Tel: +31 71 565-4426
E-mail:

Ms. Irina Bruckner
Science Programme Communication Service
European Space Agency
Tel: +31 71 565-3273
E-mail:

More about ...

* XMM-Newton overview
http://www.esa.int/esaSC/120385_index_0_m.html
* Integral overview
http://www.esa.int/esaSC/120374_index_0_m.html

Related articles

* Seeing the Universe in X-ray wavelengths
http://www.esa.int/esaSC/SEMTA2T1VED_index_0.html
* Integral's first look at the gamma-ray Universe
http://www.esa.int/esaCP/ESADW18708D_index_0.html
* What are 'dark matter' and 'dark energy'?
http://www.esa.int/esaSC/SEMLK4VZJND_index_0.html
* Seeing the Universe in the gamma-ray wavelengths
http://www.esa.int/esaSC/SEM3A2T1VED_index_0.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/export/esaCP/SEMQ..._index_1.html]

[Image 2:
http://www.esa.int/export/esaCP/SEMQ...html#subhead2]

XMM-Newton's X-ray EPIC camera shows the expanding rings caused by a flash of
X-rays scattered by dust in our Galaxy. The X-rays were produced by a powerful
gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow
of the gamma-ray burst is at the centre of the expanding rings. Other,
unrelated, X-ray sources can also be seen. The time since the gamma-ray
explosion is shown in each panel in hours. At their largest size, the rings
would appear in the sky about five times smaller than the full moon.

Credits: ESA, S. Vaughan (University of Leicester)