Andrew Yee
April 6th 06, 05:16 PM
ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
Issued by RAS Communications Officers:
Peter Bond
Tel: +44 (0)1483-268672 Fax: +44 (0)1483-274047
AND
Anita Heward
Tel: +44 (0)1483-420904
NATIONAL ASTRONOMY MEETING PRESS ROOM (4 - 7 APRIL ONLY):
Tel: +44 (0)116-229-7474 or 229-7475 or 252-3312 or 252-3531
Fax: +44 (0)116-252-3531
RAS Web site:
http://www.ras.org.uk/
RAS National Astronomy Meeting web site:
http://www.nam2006.le.ac.uk/index.shtml
CONTACT DETAILS ARE LISTED AT THE END OF THIS RELEASE.
EMBARGOED FOR 00:01 BST, WEDNESDAY 5 APRIL 2006 (23:01 GMT ON TUESDAY
4 APRIL)
Ref.: PN 06/22 (NAM 15)
SWIFT OBSERVES AN UNUSUAL BANG IN THE FAR UNIVERSE
Almost 40 years have passed since top secret nuclear weapon warning
satellites accidentally discovered bursts of high energy gamma rays
coming from space. Although many thousands of gamma ray bursts
(GRBs) have since been detected, the origin and nature of these
bursts is still not well understood.
One example of an unusual gamma ray burst occurred on 1 August 2005,
when instruments on board the NASA-UK-Italy Swift spacecraft detected
a bizarre GRB, which displayed unprecedented behaviour. Results based
on the Swift data are being presented today (Wednesday) at the RAS
National Astronomy Meeting in Leicester by Massimiliano De Pasquale
from Mullard Space Laboratory-UCL.
Gamma ray bursts take the form of a brilliant burst of radiation,
followed by a slowly fading afterglow. This shallow decay in the
X-ray and optical light curve usually lasts for several days after
the high energy explosion.
Swift data have shown that, whatever the 'central engine' that powers
the GRB may be, it does not switch off after a few seconds, but often
produces fast flares of radiation and injects energy into the outflow
for hours.
Scientists believe that most GRBs are thought to be the result of a
black hole swallowing a large star. This process might take long
enough to explain both the prompt emission of X-rays and gamma rays,
the late flares and energy injection.
The remaining matter is launched outwards at a huge velocity, but
the interstellar medium around the burst acts like a "brake" to
this outflow, being heated in the process and producing the
afterglow emission.
In the case of the August 2005 gamma ray burst, known as GRB050801
after its date of detection, there was a bright afterglow with a
steady emission both in X-ray and optical wavelengths, without any
initial, brilliant flare. This behaviour lasted for only 250 seconds
after the end of the prompt emission, before the afterglow began
the typical decline in brightness. This behaviour has never been
observed before.
The flat emission both in X-ray and optical wavelengths gives some
hints about the 'central engine' of this GRB.
"This feature might be explained if we assume that, rather than
a black hole, the core of the star has shrunk its mass and its
magnetic field into an object known as a magnetar," said
Massimiliano De Pasquale.
A magnetar is a form of neutron star, the remains of a collapsed
star that was originally about 10 times more massive than the Sun.
This extremely dense object typically has a radius of only 10 km
but the same mass of the Sun.
Magnetars are thousands of times more magnetic than ordinary neutron
stars, with a magnetic field 1,000 million million times stronger
than the Earth's. Only a few of these exotic objects are known.
"Such an object initially rotates very quickly, typically hundreds
of times every second, but it slows down by irradiating its energy
at the magnetic poles, like a lighthouse," said De Pasquale. "This
would keep the afterglow emission steady for a time scale similar
to that observed for GRB 050801.
The joint analysis of data from the XRT and UVOT instruments on
Swift has also allowed the team to determine the distance of
GRB050801, which was previously unknown, by measuring the amount
of light absorbed during its intergalactic travel en route to the
Earth.
It turns out that the burst took place 9 billion light-years away,
which means that the gamma rays, X-rays and light from the gamma
ray burst were created and began their journey across the universe
4,500 million years before the Earth was born.
"The explosion produced the same amount of energy as the Sun
produces during its entire lifetime of 10 billion years," said
Massimiliano De Pasquale.
CONTACT
Massimiliano De Pasquale
Mullard Space Science Laboratory-UCL
Holmbury St Mary
Dorking, Surrey RH5 6NT
Tel: +44 (0)1483-204177
On 5 April, Mr. De Pasquale can be contacted via the NAM press office
(see above).
NOTES FOR EDITORS
Other members of the MSSL-UCL team that studied GRB050801 are: Dr. M.
J. Page, Dr. A. J. Blustin, Dr. S. Zane, Dr. K. McGowan, Prof. K. O.
Mason and graduate student S. R. Oates.
Gamma-ray bursts are flashes of high-energy radiation that appear on
average about once a day at an unpredictable time from unpredictable
directions in the sky. These sudden and non-repeating flashes of
radiation have over 100,000 times the energy of visible light, but
only last only a few tens of seconds.
Swift, launched on 20 November 2004, is a collaboration between
NASA's Goddard Space Flight Center, Penn State University, Leicester
University and the Mullard Space Science Laboratory (both in the UK),
and the Osservatorio Astronomico di Brera in Italy.
Swift carries three main instruments: the Burst Alert Telescope
(BAT); X- ray Telescope (XRT); and the Ultraviolet/Optical Telescope
(UVOT), which make it the most sensitive gamma ray burst satellite
to date. It is also the first gamma ray burst spacecraft to have
both X-ray and optical telescopes on board and with the ability to
slew towards a GRB in only 1 minute, allowing it to study these
phenomena since the very beginning and relay very accurate and
rapid positions to astronomers on the ground.
During its operational lifetime, Swift is expected to find hundreds
of gamma ray bursts. Rapid follow-up observations using Swift and
ground-based telescopes on the ground should enable astronomers to
answer some of the most fundamental puzzles in astronomy, such as
the nature and origin of gamma ray bursts, the births of black
holes, the first stars, and the first galaxies.
The 2006 RAS National Astronomy Meeting is hosted by the University
of Leicester. It is sponsored by the Royal Astronomical Society,
the UK Particle Physics and Astronomy Research Council (PPARC), the
University of Leicester and the National Space Centre, Leicester.
IMAGES
An image sequence showing a gamma ray burst observed by NASA's
Compton Gamma Ray Observatory:
http://antwrp.gsfc.nasa.gov/apod/ap991104.html
A sequence of three false colour X-ray pictures from the
Italian/Dutch BeppoSAX satellite showing the fading glow from
a gamma ray burst:
http://antwrp.gsfc.nasa.gov/apod/ap980528.html
An optical image of a gamma ray burst in its host galaxy, billions
of light years distant:
http://antwrp.gsfc.nasa.gov/apod/ap980507.html
Short movie showing Swift observing a GRB:
http://www.nasa.gov/mpg/108544main_swift-turn-burst_NASA%20WebV_1.mpg
Issued by RAS Communications Officers:
Peter Bond
Tel: +44 (0)1483-268672 Fax: +44 (0)1483-274047
AND
Anita Heward
Tel: +44 (0)1483-420904
NATIONAL ASTRONOMY MEETING PRESS ROOM (4 - 7 APRIL ONLY):
Tel: +44 (0)116-229-7474 or 229-7475 or 252-3312 or 252-3531
Fax: +44 (0)116-252-3531
RAS Web site:
http://www.ras.org.uk/
RAS National Astronomy Meeting web site:
http://www.nam2006.le.ac.uk/index.shtml
CONTACT DETAILS ARE LISTED AT THE END OF THIS RELEASE.
EMBARGOED FOR 00:01 BST, WEDNESDAY 5 APRIL 2006 (23:01 GMT ON TUESDAY
4 APRIL)
Ref.: PN 06/22 (NAM 15)
SWIFT OBSERVES AN UNUSUAL BANG IN THE FAR UNIVERSE
Almost 40 years have passed since top secret nuclear weapon warning
satellites accidentally discovered bursts of high energy gamma rays
coming from space. Although many thousands of gamma ray bursts
(GRBs) have since been detected, the origin and nature of these
bursts is still not well understood.
One example of an unusual gamma ray burst occurred on 1 August 2005,
when instruments on board the NASA-UK-Italy Swift spacecraft detected
a bizarre GRB, which displayed unprecedented behaviour. Results based
on the Swift data are being presented today (Wednesday) at the RAS
National Astronomy Meeting in Leicester by Massimiliano De Pasquale
from Mullard Space Laboratory-UCL.
Gamma ray bursts take the form of a brilliant burst of radiation,
followed by a slowly fading afterglow. This shallow decay in the
X-ray and optical light curve usually lasts for several days after
the high energy explosion.
Swift data have shown that, whatever the 'central engine' that powers
the GRB may be, it does not switch off after a few seconds, but often
produces fast flares of radiation and injects energy into the outflow
for hours.
Scientists believe that most GRBs are thought to be the result of a
black hole swallowing a large star. This process might take long
enough to explain both the prompt emission of X-rays and gamma rays,
the late flares and energy injection.
The remaining matter is launched outwards at a huge velocity, but
the interstellar medium around the burst acts like a "brake" to
this outflow, being heated in the process and producing the
afterglow emission.
In the case of the August 2005 gamma ray burst, known as GRB050801
after its date of detection, there was a bright afterglow with a
steady emission both in X-ray and optical wavelengths, without any
initial, brilliant flare. This behaviour lasted for only 250 seconds
after the end of the prompt emission, before the afterglow began
the typical decline in brightness. This behaviour has never been
observed before.
The flat emission both in X-ray and optical wavelengths gives some
hints about the 'central engine' of this GRB.
"This feature might be explained if we assume that, rather than
a black hole, the core of the star has shrunk its mass and its
magnetic field into an object known as a magnetar," said
Massimiliano De Pasquale.
A magnetar is a form of neutron star, the remains of a collapsed
star that was originally about 10 times more massive than the Sun.
This extremely dense object typically has a radius of only 10 km
but the same mass of the Sun.
Magnetars are thousands of times more magnetic than ordinary neutron
stars, with a magnetic field 1,000 million million times stronger
than the Earth's. Only a few of these exotic objects are known.
"Such an object initially rotates very quickly, typically hundreds
of times every second, but it slows down by irradiating its energy
at the magnetic poles, like a lighthouse," said De Pasquale. "This
would keep the afterglow emission steady for a time scale similar
to that observed for GRB 050801.
The joint analysis of data from the XRT and UVOT instruments on
Swift has also allowed the team to determine the distance of
GRB050801, which was previously unknown, by measuring the amount
of light absorbed during its intergalactic travel en route to the
Earth.
It turns out that the burst took place 9 billion light-years away,
which means that the gamma rays, X-rays and light from the gamma
ray burst were created and began their journey across the universe
4,500 million years before the Earth was born.
"The explosion produced the same amount of energy as the Sun
produces during its entire lifetime of 10 billion years," said
Massimiliano De Pasquale.
CONTACT
Massimiliano De Pasquale
Mullard Space Science Laboratory-UCL
Holmbury St Mary
Dorking, Surrey RH5 6NT
Tel: +44 (0)1483-204177
On 5 April, Mr. De Pasquale can be contacted via the NAM press office
(see above).
NOTES FOR EDITORS
Other members of the MSSL-UCL team that studied GRB050801 are: Dr. M.
J. Page, Dr. A. J. Blustin, Dr. S. Zane, Dr. K. McGowan, Prof. K. O.
Mason and graduate student S. R. Oates.
Gamma-ray bursts are flashes of high-energy radiation that appear on
average about once a day at an unpredictable time from unpredictable
directions in the sky. These sudden and non-repeating flashes of
radiation have over 100,000 times the energy of visible light, but
only last only a few tens of seconds.
Swift, launched on 20 November 2004, is a collaboration between
NASA's Goddard Space Flight Center, Penn State University, Leicester
University and the Mullard Space Science Laboratory (both in the UK),
and the Osservatorio Astronomico di Brera in Italy.
Swift carries three main instruments: the Burst Alert Telescope
(BAT); X- ray Telescope (XRT); and the Ultraviolet/Optical Telescope
(UVOT), which make it the most sensitive gamma ray burst satellite
to date. It is also the first gamma ray burst spacecraft to have
both X-ray and optical telescopes on board and with the ability to
slew towards a GRB in only 1 minute, allowing it to study these
phenomena since the very beginning and relay very accurate and
rapid positions to astronomers on the ground.
During its operational lifetime, Swift is expected to find hundreds
of gamma ray bursts. Rapid follow-up observations using Swift and
ground-based telescopes on the ground should enable astronomers to
answer some of the most fundamental puzzles in astronomy, such as
the nature and origin of gamma ray bursts, the births of black
holes, the first stars, and the first galaxies.
The 2006 RAS National Astronomy Meeting is hosted by the University
of Leicester. It is sponsored by the Royal Astronomical Society,
the UK Particle Physics and Astronomy Research Council (PPARC), the
University of Leicester and the National Space Centre, Leicester.
IMAGES
An image sequence showing a gamma ray burst observed by NASA's
Compton Gamma Ray Observatory:
http://antwrp.gsfc.nasa.gov/apod/ap991104.html
A sequence of three false colour X-ray pictures from the
Italian/Dutch BeppoSAX satellite showing the fading glow from
a gamma ray burst:
http://antwrp.gsfc.nasa.gov/apod/ap980528.html
An optical image of a gamma ray burst in its host galaxy, billions
of light years distant:
http://antwrp.gsfc.nasa.gov/apod/ap980507.html
Short movie showing Swift observing a GRB:
http://www.nasa.gov/mpg/108544main_swift-turn-burst_NASA%20WebV_1.mpg