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TOPIC: Pulsars

Blobrana

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Posts: 131433

Date: Dec 11 12:26 2006

XTE J1739-285	Permalink

Title: Rotation at 1122 Hz and the neutron star structure Authors: M. Bejger, P. Haensel, J.L. Zdunik Recent observations of XTE J1739-285 suggest that it contains a neutron star rotating at 1122 Hz. Such rotation imposes bounds on the structure of neutron star in XTE J1739-285. These bounds may be used to constrain poorly known equation of state of dense matter. One-parameter families of stationary configurations rotating rigidly at 1122 Hz are constructed, using a precise 2-D code solving Einstein equations. Hydrostatic equilibrium solutions are tested for stability with respect to axi-symmetric perturbations. A set of ten diverse EOSs of neutron stars is considered. Hypothetical strange stars are also studied. For each EOS, the family of possible neutron star models is limited by the mass shedding limit, corresponding to maximum allowed equatorial radius, R_max, and by the instability with respect to the axi-symmetric perturbations, reached at the minimum allowed equatorial radius, R_min. We get R_min \simeq 10-13km, and R_max \simeq 16-18km, with allowed mass 1.4-2.3 M_\odot. Allowed stars with hyperonic or exotic-phase core are supramassive and have a very narrow mass range. Quark star with accreted crust might be allowed, provided such a model is able to reproduce X-ray bursts from XTE J1739-285. Read more (34kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Oct 19 11:33 2006

Vela-like Pulsar B1046-58	Permalink

Title: Chandra and XMM-Newton Observations of the Vela-like Pulsar B1046-58 Authors: M. E. Gonzalez, V. M. Kaspi, M. J. Pivovaroff, B. M. Gaensler We present results from Chandra and XMM-Newton observations of the radio pulsar B1046-58. A high-resolution spatial analysis reveals an asymmetric pulsar wind nebula (PWN) ~6"x11" in size. The combined emission from the pulsar and its PWN is faint, with a best-fit power-law photon index of Gamma=1.7 and unabsorbed luminosity of ~10^32 ergs/s in the 0.5-10.0 keV range (assuming a distance of 2.7 kpc). A spatially resolved imaging analysis suggests the presence of softer emission from the pulsar. No pulsations are detected from PSR B1046-58; assuming a worst-case sinusoidal pulse profile, we derive a 3 sigma upper limit for the pulsed fraction in the 0.5-10.0 keV range of 53%. Extended PWN emission is seen within 2" of the pulsar; the additional structures are highly asymmetric and extend predominantly to the south-east. We discuss the emission from the PWN as resulting from material downstream of the wind termination shock, as outflow from the pulsar or as structures confined by a high space velocity. The first two interpretations imply equipartition fields in the observed structures of ~40-100 uG, while the latter case implies a velocity for the pulsar of ~ 190 n^-½km/s (where n is the ambient number density in units of cm^-3). No emission from an associated supernova remnant is detected. Read more (373kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Jul 31 08:29 2006

Pulsars	Permalink

Title: The Parkes multibeam pulsar survey: VI. Discovery and timing of 142 pulsars and a Galactic population analysis Authors: D. R. Lorimer, A. J. Faulkner, A. G. Lyne, R. N. Manchester, M. Kramer, M. A. McLaughlin, G. Hobbs, A. Possenti, I. H. Stairs, F. Camilo, M. Burgay, N. D'Amico, A. Corongiu, F. Crawford Researchers present the discovery and follow-up observations of 142 pulsars found in the Parkes 20-cm multibeam pulsar survey of the Galactic plane. These new discoveries bring the total number of pulsars found by the survey to 742. In addition to tabulating spin and astrometric parameters, along with pulse width and flux density information, the researchers present orbital characteristics for 13 binary pulsars which form part of the new sample. Combining these results from another recent Parkes multibeam survey at high Galactic latitudes, they have a sample of 1008 normal pulsars which they use to carry out a determination of their Galactic distribution and birth rate. The researchers infer a total Galactic population of 30000 ±1100 potentially detectable pulsars (i.e. those beaming towards us) having 1.4-GHz luminosities above 0.1 mJy kpc² . Using a pulsar current analysis, they derive the birth rate of this population to be 1.4 ±0.2 pulsars per century. An important conclusion from their work is that the inferred radial density function of pulsars depends strongly on the assumed distribution of free electrons in the Galaxy. As a result, any analyses using the most recent electron model of Cordes & Lazio predict a dearth of pulsars in the inner Galaxy. The researchers show that this model can also bias the inferred pulsar scale height with respect to the Galactic plane. Combining their results with other Parkes multibeam surveys they find that the population is best described by an exponential distribution with a scale height of 330 pc. Read more (445kb, PDF) __________________

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