The discovery of a unique phenomenon: a beautiful set of expanding
X-ray halos surrounding a gamma-ray burst which have never been seen
before, (see Movie link at end), has been announced by an international
team of astronomers led by Dr Simon Vaughan of the University of
Leicester. The research has been accepted for publication in the
Astrophysical Journal.

Gamma-ray bursts (GRB) are the most energetic form of radiation in the
Universe and can be used to probe any material between Earth and the
burst. In this case, the GRB lies behind the plane of our Galaxy, so its
light has to travel through the gas and dust in the Galactic disc to
reach us.

ESA’s gamma ray observatory satellite ‘Integral’ detected the 30 second
long GRB 031203 on December 3rd 2003 and the halos were discovered in a
follow-up observation that started 6 hours after the burst with ESA’s
‘XMM-Newton’ X-ray space telescope.

Commenting on the discovery, Professor Ian Halliday, Chief Executive of
the UK’s Particle Physics and Astronomy Research Council (PPARC) said
“Gamma-ray bursts are the most violent events in the Universe. Unlike
the serene beauty of the stars that we can see with our eyes, the Gamma
Ray Universe is a place of dramatic explosions, cosmic collisions and
matter being sucked into black holes.”

Halliday added “This is a wonderful example of two of ESA’s most
advanced observatories in which UK scientists have made a significant
contribution, working in harmony to reveal a new level of scientific
understanding.”

The fading X-ray emission from the GRB – the afterglow – is clearly
seen in the image from the X-ray cameras on XMM-Newton. Uniquely, two
rings centred on the afterglow were also seen. Dr Vaughan said “These
rings are due to dust in our own Galaxy which is illuminated by the
X-rays from the gamma-ray burst. The dust scatters some of the X-rays
causing the rings, in the same way as fog scatters the light from a
car’s headlights.” He added “It’s like a shout in a cathedral; the
shout of the gamma-ray burst is louder, but the Galactic reverberation,
seen as the rings, is more beautiful.”

Due to the finite speed of light, X-rays from more distant dust reach
us later, giving rise to the appearance of expanding rings. Dr Vaughan
said “We expect to see an expanding ring on the sky if the dust is in a
sheet roughly in the plane of the sky, but as we see two rings there
must be two dust sheets between us and the GRB. Understanding how dust
is distributed in our Galaxy is important. Dust helps cool gas clouds
which can then collapse to form stars and planets. Knowing where dust is
located helps astronomers determine where star and planet formation is
likely to occur.”

Expanding X-ray dust scattering rings have never been seen before.
Slower moving rings seen in visible light around a very few supernovae
are caused by a similar effect.

The two halos are due to thin sheets of dust at 2,900 and 4,500
light-years away; the astronomers accurately measured the distances from
the expansion rate of the halos. The distances have an uncertainty of
just 2%, a remarkable level of accuracy for an object in our Galaxy. The
nearest dust sheet is probably part of the Gum nebula, a bubble of hot
gas resulting from many supernova explosions. The GRB itself is thought
to have occurred in a small galaxy about a billion light-years away (one
of the closest GRB galaxies).

Astronomers are still trying to understand the mysterious gamma-ray
bursts. 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 GRB.

Today Integral and XMM-Newton provide astronomers with their most
powerful facilities for studying gamma-ray bursts, but 2004 will see the
launch of “Swift”, a new NASA mission with major UK involvement, which
will be dedicated to GRBs. This will work in concert with the two ESA
satellite observatories, providing more opportunities for discoveries in
this cutting edge field. UK participation in Integral, XMM-Newton and
Swift is funded by the Particle Physics and Astronomy Research Council.

Notes to Editors
The EPIC X-ray cameras on XMM-Newton used in this observation were
provided by an international team led by Dr Martin Turner of the
University of Leicester. Dr Martin Turner was awarded a CBE in the UK
2004 New Years Honours list for services to X-ray astronomy.

Astrophysics research at the University of Leicester is funded by the
UK Particle Physics and Astronomy Research Council. XMM-Newton and
Integral are ESA science missions funded by European Space Agency member
states and the USA (NASA).

Resources

Movie: XMM-Newton observational data:
http://www.star.le.ac.uk/~sav2/anim.gif

Higher Resolution http://www.star.le.ac.uk/~sav2/anim_hi.gif

Caption: 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 seconds. At their largest size, the rings would appear in the
sky about five times smaller than the full moon.
Credit: ESA, S. Vaughan (University of Leicester)

Still images:
XMM-Newton observational data – 4 panel image:
http://www.star.le.ac.uk/~sav2/grb031203/4panel.gif
Caption: 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.
Credit: ESA, S. Vaughan (University of Leicester)

Contacts:

University of Leicester
Dr Simon Vaughan
Email sav2@star.le.ac.uk
Tel +44 (0)116 2523510
Web: http://www.star.le.ac.uk/~sav2/grb031203/

Dr Dick Willingale
Email rw@star.le.ac.uk
Tel +44 (0)116 2523556

Dr Paul O’Brien
Email pto@star.le.ac.uk
Tel +44 (0)116 2525203

Dr Julian Osborne
Email julo@star.le.ac.uk
Tel +44 (0)116 2523598

ESA
Dr. Fred Jansen
XMM-Newton Project Scientist
European Space Agency
Tel: +31 71 5654426
E-mail: fjansen@rssd.esa.int

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

PPARC Press Office
Julia Maddock
Email Julia.maddock@pparc.ac.uk
Tel +44 (0) 1793 442094

Web pages:

University of Leicester, Dept of Physics & Astronomy:
http://www.star.le.ac.uk or http://www.star.le.ac.uk/news/0204.html
XMM-Newton control centre: http://xmm.vilspa.esa.es/

XMM-Newton science:
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=23

Integral control centre: http://astro.estec.esa.nl/Integral/

Swift project: http://swift.gsfc.nasa.gov/

The Particle Physics and Astronomy Research Council (PPARC) is the
UK’s strategic science investment agency. It funds research,
education and public understanding in four broad areas of science –
particle physics, astronomy, cosmology and space science.

PPARC is government funded and provides research grants and
studentships to scientists in British universities, gives researchers
access to world-class facilities and funds the UK membership of
international bodies such as the European Organisation for Nuclear
Research, CERN, the European Space Agency and the European Southern
Observatory. It also contributes money for the UK telescopes overseas on
La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology
Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National
Facility.