* Astronomy

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RE: The Crab Nebula

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Nasa releases spectacular new image of Crab Nebula
It is the product of a cosmic collaboration, combining data from the Chandra X-ray Observatory, the Hubble Space Telescope, and the Spitzer Space Telescope.

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A star's spectacular death in the constellation Taurus was observed on Earth as the supernova of 1054 A.D. Now, almost a thousand years later, a super dense object -- called a neutron star -- left behind by the explosion is seen spewing out a blizzard of high-energy particles into the expanding debris field known as the Crab Nebula. X-ray data from Chandra provide significant clues to the workings of this mighty cosmic "generator," which is producing energy at the rate of 100,000 suns.
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The Crab Nebula

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NASA's Chandra X-ray Observatory has provided the first clear view of the faint boundary of the Crab Nebula's X-ray-emitting pulsar wind nebula.
The nebula is powered by a rapidly-rotating, highly-magnetised neutron star, or "pulsar". The combination of rapid rotating and strong magnetic field generates an intense electromagnetic field that creates jets of matter and anti-matter moving away from the north and south poles of the pulsar, and an intense wind flowing out in the equatorial direction.
The inner X-ray ring is thought to be a shock wave that marks the boundary between the surrounding nebula and the flow of matter and antimatter particles from the pulsar. Energetic electrons and positrons (antielectrons) move outward from this ring to brighten the outer ring and produce an extended X-ray glow.

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A powerful cosmic particle accelerator has been pinpointed in the Crab Nebula: a doughnut-shaped magnetic field surrounding the stellar corpse at the nebula's heart. The finding is based on a tricky measurement showing that high-energy radiation near the star is polarised, with its electric field lining up neatly with the star's spin axis.

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Title: Beating the spin-down limit on gravitational wave emission from the Crab pulsar
Authors: The LIGO Scientific Collaboration: B. Abbott, et al

We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first nine months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms.

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New information about the heart of one of the most famous objects in the sky -- the Crab Pulsar in the Crab Nebula -- has been revealed by an international team of scientists searching for gravitational waves. The team's achievement also is the first direct look into the interior of a neutron star.

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The search for gravitational waves has revealed new information about the core of one of the most famous objects in the sky: the Crab Pulsar in the Crab Nebula.
An analysis by the international LIGO (Laser Interferometer Gravitational-Wave Observatory) Scientific Collaboration, to be submitted to Astrophysical Journal Letters, has shown that although the pulsar is losing energy at a rapid rate, less than 4% of this energy loss is caused by gravitational waves.
This means that for the Crab Pulsar, gravitational waves are not the dominant mechanism causing it to slow down. It also means that the shape of the pulsar must be very symmetrical with a surface varying by less than a metre. The physical mechanisms for energy loss and the accompanying braking of the pulsar spin rate have been hypothesized to be asymmetric particle emission, magnetic dipole radiation, and gravitational-wave emission.

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Title: Observation of the Crab Nebula with the MAGIC telescope
Authors: A. Nepomuk Otte, for the MAGIC collaboration

We report about very high energy (VHE) gamma-ray observations of the Crab Nebula with the MAGIC telescope. The gamma-ray flux from the nebula was measured between 60 GeV and 9 TeV. The energy spectrum can be described with a curved power law dF/dE=f_0 (E/300GeV)^(a+b log10(E/300GeV)) with a flux normalization f_0 of (6.0 ±0.2stat)*10^-10 cm^-2 s^-1 TeV^-1, a=-2.31 ±0.06stat and b=-0.26 ±0.07stat. The position of the IC-peak is determined at 77 ±47 GeV. Within the observation time and the experimental resolution of the telescope, the gamma-ray emission is steady and pointlike. The emission's centre of gravity coincides with the position of the pulsar. Pulsed gamma-ray emission from the pulsar could not be detected. We constrain the cutoff energy of the spectrum to be less than ~30 GeV, assuming that the differential energy spectrum has an exponential cutoff. For a super-exponential shape, the cutoff energy can be as high as ~60GeV.

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