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TOPIC: Pulsars


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Millisecond Pulsars
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Millisecond Pulsars (MSP) are dense, highly magnetised dead stars with a rotational period ranging from one to 10 milliseconds, emitting radio waves somewhat similar to lighthouse beams. However, only the microwave or X-ray portions of the electromagnetic spectrum of the MSP can be viewed. Till date, their origin was a mystery to experts, and there were several existing theories about the same.
Now, however, a team of astronomers have come up with a logical reason about how the MSP evolved. As per the report published in the journal Science by the researchers at National Radio Astronomy Observatory (NRAO), the MSP originated from a type of binary star system that spews out X-rays. The nine year long experiment conducted by the team, found that old pulsars emit X-rays first, followed by radio pulses after the new MSP collects mass from its neighbouring star.


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RE: Pulsars
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A pulsar is a highly magnetised neutron star, with a radius of 10-15 km, having somewhat greater mass than the Sun which has a radius of approximately 1 million km. Radiation is beamed out along the magnetic poles and pulses of radiation are received as the beam crosses the Earth, in the same manner as the beam from a lighthouse causes flashes. Being enormous cosmic flywheels with a tick attached, they make some of the best clocks known to mankind.

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Discovery of 28 pulsars
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Title: Discovery of 28 pulsars using new techniques for sorting pulsar candidates
Authors: M.J. Keith, R.P. Eatough, A.G. Lyne, M. Kramer, A. Possenti, F. Camilo, R.N. Manchester

Modern pulsar surveys produce many millions of candidate pulsars, far more than can be individually inspected. Traditional methods for filtering these candidates, based upon the signal-to-noise ratio of the detection, cannot easily distinguish between interference signals and pulsars. We have developed a new method of scoring candidates using a series of heuristics which test for pulsar-like properties of the signal. This significantly increases the sensitivity to weak pulsars and pulsars with periods close to interference signals. By applying this and other techniques for ranking candidates from a previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously unknown pulsars have been discovered. These include an eccentric binary system and a young pulsar which is spatially coincident with a known supernova remnant.

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RE: Pulsars
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Since their discovery 40 years ago, pulsars - the rapidly spinning, highly magnetized crushed cores of exploded stars - have largely been detected via the pulsing radio signals emitted by their lighthouse beam-like jets. But astronomers have suspected that these pulses give only the slightest hint of the true power of these cosmic dynamos.
With the launch of NASA's Fermi Gamma-ray Space Telescope (formerly GLAST) in June of last year, scientists are finally getting a glimpse of the powerful hearts of these stellar beasts. In its first four months of operation, Fermi detected more than three dozen pulsars, 12 of which are new gamma-ray-only pulsars.


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NASA's Fermi Gamma-ray Space Telescope has discovered 12 new gamma-ray-only pulsars and has detected gamma-ray pulses from 18 others. The finds are transforming our understanding of how these stellar cinders work.

"We know of 1,800 pulsars, but until Fermi we saw only little wisps of energy from all but a handful of them. Now, for dozens of pulsars, we're seeing the actual power of these machines" - Roger Romani of Stanford University, Californis.

A pulsar is a rapidly spinning and highly magnetised neutron star, the crushed core left behind when a massive sun explodes. Most were found through their pulses at radio wavelengths, which are thought to be caused by narrow, lighthouse-like beams emanating from the star's magnetic poles.

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Telescope sees pulsar that winks back with gamma-ray beams

gamma

Gamma rays from a spinning neutron star, shining through the remnants of a supernova, have been detected by the Fermi space telescope.

About three times a second, the rotating corpse of a 10,000-year-old star sweeps a beam of gamma rays toward Earth. This object, known as a pulsar, is the first one known to "blink" at Earth only in gamma rays, and was discovered by an orbiting observatory launched in June with significant involvement from researchers at Stanford and the SLAC National Accelerator Laboratory.

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We present a detailed analysis of the high-energy gamma-ray source 2EG J0008+7307. The source has a steady flux and a hard spectrum, softening above 2 GeV. The properties of the gamma-ray source are suggestive of emission from a young pulsar in the spatially coincident CTA 1 supernova remnant, which has recently been found to have a non-thermal X-ray plerion.

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2EG J0008+7307
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First gamma-ray-only pulsar observation opens new window on stellar evolution
About three times a second, a 10,000-year-old stellar corpse sweeps a beam of gamma-rays toward Earth. This object, known as a pulsar, is the first one known to blink only in gamma rays, and was discovered by the Large Area Telescope (LAT) onboard NASAs Fermi Gamma-ray Space Telescope, a collaboration with the US Department of Energy (DOE) and international partners.

This is the first example of a new class of pulsars that will give us fundamental insights into how stars work - Stanford Universitys Peter Michelson, principal investigator for the LAT.

The LAT data is processed by the DOEs SLAC National Accelerator Laboratory and analysed by the International LAT Collaboration.
The gamma-ray-only pulsar lies within a supernova remnant known as CTA 1, which is located about 4600 light-years away in the constellation Cepheus. Its lighthouse-like beam sweeps Earths way every 316.86 milliseconds and emits 1000 times the energy of our sun. These results appear in the Oct. 16 edition of Science Express.

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Neutron stars
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According to current theoretical ideas, neutron stars are created when normal stars of between about four and 10 times the mass of the sun undergo supernova explosions and throw off most of their outer material. The remaining protons and electrons collapse under the action of gravity and are fused together to form a dense ball of neutrons.
When pulsating stars, also known as pulsars, were accidentally discovered by Jocelyn Bell in 1967, it was quickly realised by Thomas Gold that the really massive ones had to be spinning neutron stars. Almost 2,000 such neutron stars have been detected to date, and a typical neutron star mass is about 1.5 times the mass of our sun.

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B0834+06 and B0826-34
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Title: XMM-Newton Observations of Radio Pulsars B0834+06 and B0826-34 and Implications for Pulsar Inner Accelerator
Authors: J.Gil, F.Haberl, G.Melikidze, U.Geppert, B.Zhang, G. Melikidze Jr

We report the X-ray observations of two radio pulsars with drifting subpulses: B0834 + 06 and B0826 - 34 using \xmm\. PSR B0834 + 06 was detected with a total of 70 counts from the three EPIC instruments over 50 ks exposure time. Its spectrum was best described as that of a blackbody (BB) with temperature T_s=(2.0^{+2.0}_{-0.9}) x 10^6 K and bolometric luminosity of L_b=(8.6^{+14.2}_{-4.4}) x 10^{28} erg s^{-1}. As it is typical in pulsars with BB thermal components in their X-ray spectra, the hot spot surface area is much smaller than that of the canonical polar cap, implying a non-dipolar surface magnetic field much stronger than the dipolar component derived from the pulsar spin-down (in this case about 50 times smaller and stronger, respectively). The second pulsar PSR B0826 - 34 was not detected over 50 ks exposure time, giving an upper limit for the bolometric luminosity L_b \leq 1.4 x 10^{29} erg s^{-1}. We use these data as well as the radio emission data concerned with drifting subpulses to test the Partially Screened Gap (PSG) model of the inner accelerator in pulsars.

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