Echoes of Giant Pulses from the Crab Pulsar

Blob · #1 (**permalink**) 08-January-2007, 09:11 PM

Title: Echoes of Giant Pulses from the Crab Pulsar
Authors: J. H. Crossley, J. A. Eilek, T. H. Hankins

We have detected occasional, short-lived ''echoes'' of giant pulses from the Crab pulsar. These echo events remind us of previously reported echoes from this pulsar, but they differ significantly in detail. Our echo events last at most only a few days; the echo emission lags the primary emission by only 40-100 musec. The echoes are consistently weaker and broader than the primary emission, and appear only at the lower of our two simultaneous observing frequencies. We suggest that these echoes are created by refraction in small plasma structures -- plasma clouds or magnetic flux ropes -- deep within the Crab nebula. If this is true, our echoes provide a new probe of small-scale structures within the inner synchrotron nebula.

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Blob · #2 (**permalink**) 09-January-2007, 01:36 AM

Quote:

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.

Blob · #3 (**permalink**) 09-January-2007, 03:50 AM

Quote:

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.

Blob · #4 (**permalink**) 14-March-2007, 10:12 PM

Quote:

A new image of the Crab Nebula supernova remnant taken using the Prime Focus Camera (Suprime-Cam) on the Subaru telescope highlights the beauty of stellar debris expanding away from the site of this ancient blast. The high-resolution image captures details of an elongated tendril of gas rushing out at roughly 1,500 kilometres per second. While the nebula has been observed many times using both ground- and space-based telescopes, this image is giving astronomers another opportunity to study the mechanics of the expanding gas in much greater detail.

trinitree88 · #5 (**permalink**) 14-March-2007, 11:56 PM

Quote:

Originally Posted by Blob

Blob. I disagree. The asymmetry in the polar emissions is not only unexpected, it is expected. Neutron half-life drops precipitously in the presence of high strength magnetic fields, of the order of 10¹¹ to 10¹³ Gauss. As neutron decay is a weak interaction, and parity effects, universally seen in every run of every weak interaction ever seen, are present here, one expects the rates from the two poles to be different, and hence asymmetrical.
The same type of asymmetry dictates the ejection of the nascent pulsar from it's birthplace, with a coefficient of correlation between residual field strength and transverse velocity running to about 0.70.(Bailes et al, Monthly Notices of the Royal Astronomical Society, "A survey of Six Southern Pulsars") Anything higher than 0.3 is statistically significant.
It would seem imprudent to suggest a double pole set when parity covers it neatly. Pete.

Jerry · #6 (**permalink**) 24-June-2008, 06:16 PM

Simultaneous Absolute Timing of the Crab Pulsar at Radio and
Optical Wavelengths

http://xxx.lanl.gov/PS_cache/arxiv/p...806.3634v1.pdf

Quote:

Originally Posted by Oosterbroek et al.

Current models for high-energy pulsar emission (e.g. Dyks & Rudak 2003), describe the peaks as caustics: special relativity effects (aberration of emission directions and time of flight delays due to the finite speed of light) cause photons emitted at different altitudes to pile up at the same pulse phase. It is difficult if not contrived to imagine how caustics originating from the trailing edge extending along the full length of the open field lines within the magnetosphere could produce phase bunching yielding a commonmain peak cusp spanning 7 orders of magnitude in photon energy from incoherent synchrotron emission, and less than 1% in phase difference from coherent radio emitting sources, spanning in this case some 12 orders in photon energy. As such arguments are usually presented in the context of outer gap or slot gap model formalisms, these new results argue strongly for a localised source for the observed multiwavelength emission from the Crab pulsar.

Amazing. This means any 'whip cracking' theories for the origin of pulses are unlikely to be correct, the energy source must be highly concentrated - central to the crab core.

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