* Astronomy

Title: What makes the Crab pulsar shine?
Authors: J. A. Eilek, T. H. Hankins

Our high time resolution observations of individual pulses from the Crab pulsar show that the main pulse and interpulse differ in temporal behaviour, spectral behaviour, polarization and dispersion. The main pulse properties are consistent with one current model of pulsar radio emission, namely, soliton collapse in strong plasma turbulence. The high-frequency interpulse is quite another story. Its dynamic spectrum cannot easily be explained by any current emission model; its excess dispersion must come from propagation through the star's magnetosphere. We suspect the high-frequency interpulse does not follow the ``standard model'', but rather comes from some unexpected region within the star's magnetosphere. Similar observations of other pulsars will reveal whether the radio emission mechanisms operating in the Crab pulsar are unique to that star, or can be identified in the general population.

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The neutron star inside the Crab Nebula may have four magnetic poles, rather than the usual two – unlike any other astronomical object known. The poles may have somehow been frozen into the neutron star when it was formed in a supernova explosion.

Because the primary pulse emission lasts just 0.4 nanoseconds, it may arise in an extremely small region just 12 centimetres across, where a cloud of plasma is trapped above the surface of the neutron star.
If this conclusion is correct, the grapefruit-sized patch would be the tiniest individual object ever observed in astronomy.

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-- Edited by Blobrana at 03:43, 2007-01-09

Bizarre emission spectrum leads to speculation: Is this a third magnetic pole? SEATTLE – Astronomers and physicists using the Cornell-managed Arecibo Telescope in Puerto Rico have discovered radio interpulses from the Crab Nebula pulsar that feature never-before-seen radio emission spectra. This leads scientists to speculate this could be the first cosmic object with a third magnetic pole.

"We never see the strange frequency structure in the main pulse and we never see the really short blasts in the interpulse. We fully expected the main pulse and interpulse to be spectrally identical, but what we found is that they are very different. This is the first time seeing this in a pulsar" - Tim Hankins, acting director of the Arecibo Observatory and a co-investigator on this research.

Hankins, who also is an emeritus professor of physics at New Mexico Tech in Socorro, N.M., will present a poster, "Radio Emission Signatures in the High Frequency Interpulse of the Crab Pulsar," which he made with Jean Eilek, New Mexico Tech professor of physics, on Jan. 8, 2007, at the American Astronomical Society (AAS) convention in Seattle.

"This is a cool result. The fact that the 'left hand' and the 'right hand' of the pulsar – or the north and south magnetic poles – don't know what each other is doing, is very striking. It knocks just about every existing theory of pulsar radio emission for a loop" - Jean Eilek.

Because pulses from north and south poles should be identical, Eilek thinks this strange radio emission might be coming from another part of the pulsar. She speculates: "Maybe we've discovered an unknown, unexpected 'third magnetic pole' somewhere else in the star."

Pulsars are important to understand as they allow physicists to confirm Albert Einstein's Theory of Relativity. The magnetic and electrical fields of pulsars are far stronger than any laboratory can generate, and Hankins admits this is a difficult physics problem to understand.
In the case of the Crab Nebula pulsar, located in the constellation Taurus, some 6,300 light years from Earth, the numbers boggle the mind: Plasma clouds in the pulsar's atmosphere send out the radio emission blasts in times as short as four-tenths of a nanosecond. This plasma cloud is smaller than a soccer ball. During their short lifetimes, their blasts of radio emission can be as powerful as 10 percent of the power of our sun

"These strange emission features are not showing up in other pulsars. Maybe the magnetic field is not as simple as we think. Right now, we're totally perplexed" -Jean Eilek.

The researchers have been using Arecibo on several observation occasions, between 2004 and the present. They last conducted observations in December 2006.
New Mexico Tech students Jared Crossley, Eric Plum and James Sheckard assisted in this research. Cornell's National Astronomy and Ionosphere Centre manages Arecibo Observatory for the National Science Foundation, which funded this research.

Source: Cornell University