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TOPIC: Pulsars
Blobrana


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Posts: 131433
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RE: Pulsars
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Title: Observations of pulsars at 9 millimetres
Authors: O. Loehmer (1), A. Jessner (1), M. Kramer (2), R. Wielebinksi (1), O. Maron (3) (1-Max-Planck-Institut fuer Radioastronomie, Bonn, Germany, 2-University of Manchester, Jodrell Bank Centre for Astrophysics, UK, 3-J. Kepler Astronomical Centre, Zielona Gora, Poland)

The behaviour of the pulsar spectrum at high radio frequencies can provide decisive information about the nature of the radio emission mechanism. We report recent observations of a selected sample of pulsars at lambda=9mm (32 GHz) with the 100-m Effelsberg radio telescope. Three pulsars, PSR B0144+59, PSR B0823+26, and PSR B2022+50, were detected for the first time at this frequency. We confirm the earlier flux density measurements for a sample of six pulsars, and we are able to place upper flux density limits for another 12 pulsars. We find that all pulsar spectra have a simple form that can be described using only three parameters, one of which is the lifetime of short nano-pulses in the emission region. The study of the transition region from coherent to incoherent emission needs further and more sensitive observations at even higher radio frequencies.

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Blobrana


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Posts: 131433
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Title: B1757-24 and B1951+32: Implications for Ages and Associations
Authors: B. R. Zeiger, W. F. Brisken, S. Chatterjee, W. M. Goss
(Version v2)

Over the last decade, considerable effort has been made to measure the proper motions of the pulsars B1757-24 and B1951+32 in order to establish or refute associations with nearby supernova remnants and to understand better the complicated geometries of their surrounding nebulae. We present proper motion measurements of both pulsars with the Very Large Array, increasing the time baselines of the measurements from 3.9 yr to 6.5 yr and from 12.0 yr to 14.5 yr, respectively, compared to previous observations. We confirm the non-detection of proper motion of PSR B1757-24, and our measurement of (mu_a, mu_d) = (-11 ± 9, -1 ± 15) mas yr^{-1} confirms that the association of PSR B1757-24 with SNR G5.4-1.2 is unlikely for the pulsar characteristic age of 15.5 kyr, although an association can not be excluded for a significantly larger age. For PSR B1951+32, we measure a proper motion of (mu_a, mu_d) = (-28.8 ± 0.9, -14.7 ± 0.9) mas yr^{-1}, reducing the uncertainty in the proper motion by a factor of two compared to previous results. After correcting to the local standard of rest, the proper motion indicates a kinetic age of ~51 kyr for the pulsar, assuming it was born near the geometric centre of the supernova remnant. The radio-bright arc of emission along the pulsar proper motion vector shows time-variable structure, but moves with the pulsar at an approximately constant separation ~2.5", lending weight to its interpretation as a shock structure driven by the pulsar.

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Blobrana


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Posts: 131433
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Neutron stars
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Neutron stars and black holes aren't all they've been thought to be.
In fact, neutron stars can be considerably more massive than previously believed, and it is more difficult to form black holes, according to new research developed by using the Arecibo Observatory in Arecibo, Puerto Rico. Paulo Freire, an astronomer from the observatory, presented his research at the American Astronomical Society national meeting in Austin, Texas, Jan. 11.
In the cosmic continuum of dead, remnant stars, the Arecibo astronomers have increased the mass limit for when neutron stars turn into black holes.

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Blobrana


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Posts: 131433
Date:
RE: Pulsars
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Pulsar



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Blobrana


L

Posts: 131433
Date:
Neutron stars
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XMM-Newton has given astronomers and physics a valuable new insight into the most exotic stars in the Universe. Known as neutron stars, the composition of these extremely dense stellar objects has always been something of a puzzle. Now, XMM-Newton has revealed that they almost certainly resemble over-sized atomic nuclei.
 Natalie Webb and Didier Barret, Centre dEtude Spatiale des Rayonnements, Toulouse, France, have used XMM-Newtons EPIC camera to find three previously undiscovered neutron stars and accurately measure the quantity of various X-rays coming from the their surfaces. They were then able to compare their results with theoretical predictions to deduce the internal composition of the neutron stars. All three neutron stars lie in globular clusters of stars that orbit the centre of our galaxy.

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Blobrana


L

Posts: 131433
Date:
RE: Pulsars
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Title: Proper Motions of PSRs B1747-24 and B1951+32: Implications for Ages and Associations
Authors: B. R. Zeiger, W. F. Brisken, S. Chatterjee, W. M. Goss

Over the last decade, considerable effort has been made to measure the proper motions of the pulsars B1757-24 and B1951+32 in order to establish or refute associations with nearby supernova remnants and to understand better the complicated geometries of their surrounding nebulae. We present proper motion measurements of both pulsars with the Very Large Array, increasing the time baselines of the measurements from 3.9 yr to 6.5 yr and from 12.0 yr to 14.5 yr, respectively, compared to previous observations. We confirm the non-detection of proper motion of PSR B1757-24, and our measurement of (mu_a, mu_d) = (-11 ± 9, -1 ± 15) mas yr^{-1} confirms that the association of PSR B1757-24 with SNR G5.4-1.2 is unlikely for the pulsar characteristic age of 15.5 kyr, although an association can not be excluded for a significantly larger age. For PSR B1951+32, we measure a proper motion of (mu_a, mu_d) = (-28.8 ± 0.9, -14.7 ± 0.9) mas yr^{-1}, reducing the uncertainty in the proper motion by a factor of two compared to previous results. After correcting to the local standard of rest, the proper motion indicates a kinetic age of ~51 kyr for the pulsar, assuming it was born near the geometric centre of the supernova remnant. The radio-bright arc of emission along the pulsar proper motion vector shows time-variable structure, but moves with the pulsar at an approximately constant separation ~2.5", lending weight to its interpretation as a shock structure driven by the pulsar.

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Blobrana


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Posts: 131433
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XTE J1739-285
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Title: Is XTE J1739-285 a quark star masquerading as a neutron star
Authors: Zheng Xiaoping, Pan Nana, Zhang Li

The recent discovery of burst oscillation at 1122Hz in the X-ray transient XTE J1739-285 supports the suggestion that it contains a submillisecond pulsar. We here find for the first time the enormous dissipation effect in the transition boundary layer between quark matter core and hadron matter envelope. Just combining the estimation with previous dissipation mechanism together, we show that XTE J1739-285 can be uniquely restricted to a quark star masquerading as a neutron star (hybrid star) that contains a pure quark matter or mixed quark-hadron matter core from synthesising both gravitational wave radiation (r-mode) instability and Keplerian motion constraints at 1122Hz lever. Such constraints allow the radii in the range 9 km R 12 km and the masses in the range 1.2 solar masses M   2.0 solar masses. The normal neutron stars, hyperon stars and strange stars within the mass-radius limits are excluded.

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Blobrana


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Posts: 131433
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PSR B1737-30
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Title: Observations of Six Glitches in PSR B1737-30
Authors: W. Z. Zou, N. Wang, R. N. Manchester, J. O. Urama, G. Hobbs, Z. Y. Liu, J. P. Yuan

Six glitches have been recently observed in the rotational frequency of the young pulsar PSR B1737-30 (J1740-3015) using the 25-m Nanshan telescope of Urumqi Observatory. With a total of 20 glitches in 20 years, it is one of the most frequently glitching pulsars of the about 1750 known pulsars. Glitch amplitudes are very variable with fractional increases in rotation rate ranging from 10^{-9} to 10^{-6}. Inter-glitch intervals are also very variable, but no relationship is observed between interval and the size of the preceding glitch. There is a persistent increase in |\dot\nu|, opposite in sign to that expected from slowdown with a positive braking index, which may result from changes in the effective magnetic dipole moment of the star during the glitch.

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Blobrana


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Posts: 131433
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RE: Pulsars
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Title: Theory of cooling neutron stars versus observations
Authors: D. G. Yakovlev (1,2), O. Y. Gnedin (3), A. D. Kaminker (1), A. Y. Potekhin (1,4) ((1) Ioffe Institute, St. Petersburg; (2) JINA, Notre Dame; (3) University of Michigan; (4) CRAL, ENS-Lyon)

We review current state of neutron star cooling theory and discuss the prospects to constrain the equation of state, neutrino emission and superfluid properties of neutron star cores by comparing the cooling theory with observations of thermal radiation from isolated neutron stars.

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Blobrana


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Posts: 131433
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 Early detection of the pulsar phenomenon
About a dozen sources spotted by Schisler
Schisler not the only one to pre-discover pulsars
It was one of the most important astronomical discoveries of the 20th century, and it became one of the more controversial when only one of the discoverers received a Nobel Prize.
Now a fascinating new footnote has been added to the story of how pulsars were discovered with the revelation that some had previously been observed by a U.S. Air Force staff sergeant at a remote Alaskan outpost.

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