12,726 research outputs found
Discovery of 14 radio pulsars in a survey of the Magellanic Clouds
A systematic survey of the Large and Small Magellanic Clouds for radio
pulsars using the Parkes radio telescope and the 20-cm multibeam receiver has
resulted in the discovery of 14 pulsars and the redetection of five of the
eight previously known spin-powered pulsars believed to lie in the Magellanic
Clouds. Of the 14 new discoveries, 12 are believed to lie within Clouds, three
in the Small Cloud and nine in the Large Cloud, bringing the total number of
known spin-powered pulsars in the Clouds to 20. Averaged over all positions
within the survey area, the survey had a limiting flux density of about 0.12
mJy. Observed dispersion measures suggest that the mean free electron density
in the Magellanic Clouds is similar to that in the disk of our Galaxy. The
observed radio luminosities have little or no dependence on pulsar period or
characteristic age and the differential luminosity function is consistent with
a power-law slope of -1 as is observed for Galactic pulsars.Comment: In press, Ap
Detection of X-ray emission from the host clusters of 3CR quasars
We report the detection of extended X-ray emission around several powerful
3CR quasars with redshifts out to 0.73. The ROSAT HRI images of the quasars
have been corrected for spacecraft wobble and compared with an empirical
point-spread function. All the quasars examined show excess emission at radii
of 15 arcsec and more; the evidence being strong for the more distant objects
and weak only for the two nearest ones, which are known from other wavelengths
not to lie in strongly clustered environments. The spatial profiles of the
extended component is consistent with thermal emission from the intracluster
medium of moderately rich host clusters to the quasars. The total luminosities
of the clusters are in the range 4x10^44 - 3x10^45 erg/s, assuming a
temperature of 4keV. The inner regions of the intracluster medium are, in all
cases, dense enough to be part of a cooling flow.Comment: 21 pages including 4 figures and 4 tables. To be published in MNRA
PCV115 The Sensitivity of Pro's in Evaluating Adverse Events in People Receiving “Statin” Therapy
Discovery of Two High-Magnetic-Field Radio Pulsars
We report the discovery of two young isolated radio pulsars with very high
inferred magnetic fields. PSR J1119-6127 has period P = 0.407 s, and the
largest period derivative known among radio pulsars, Pdot = 4.0e-12. Under
standard assumptions these parameters imply a characteristic spin-down age of
only tau = 1.6 kyr and a surface dipole magnetic field strength of B = 4.1e13
G. We have measured a stationary period-second-derivative for this pulsar,
resulting in a braking index of n = 2.91+-0.05. We have also observed a glitch
in the rotation of the pulsar, with fractional period change Delta_P/P =
-4.4e-9. Archival radio imaging data suggest the presence of a previously
uncataloged supernova remnant centered on the pulsar. The second pulsar, PSR
J1814-1744, has P = 3.975 s and Pdot = 7.4e-13. These parameters imply tau = 85
kyr, and B = 5.5e13 G, the largest of any known radio pulsar.
Both PSR J1119-6127 and PSR J1814-1744 show apparently normal radio emission
in a regime of magnetic field strength where some models predict that no
emission should occur. Also, PSR J1814-1744 has spin parameters similar to the
anomalous X-ray pulsar (AXP) 1E 2259+586, but shows no discernible X-ray
emission. If AXPs are isolated, high magnetic field neutron stars
(``magnetars''), these results suggest that their unusual attributes are
unlikely to be merely a consequence of their very high inferred magnetic
fields.Comment: 7 pages, 3 embedded EPS figures, to be published in Ap
A numerical investigation of the flow structures and losses for turbulent flow in 90º elbow bends
Timing the Parkes Multibeam Pulsars
Measurement of accurate positions, pulse periods and period derivatives is an
essential follow-up to any pulsar survey. The procedures being used to obtain
timing parameters for the pulsars discovered in the Parkes multibeam pulsar
survey are described. Completed solutions have been obtained so far for about
80 pulsars. They show that the survey is preferentially finding pulsars with
higher than average surface dipole magnetic fields. Eight pulsars have been
shown to be members of binary systems and some of the more interesting results
relating to these are presented.Comment: 6 pages, 2 embedded EPS figures, to be published in proceedings of
"Pulsar Astronomy - 2000 and Beyond", ASP Conf. Se
Formaldehyde over the central Pacific during PEM-Tropics B
Formaldehyde, CH2O, mixing ratios are reported for the central Pacific troposphere from a series of 41 flights, which took place in March-April 1999 as part of the NASA Pacific Exploratory Mission (PEM) -Tropics B mission. Ambient CH2O was collected in aqueous media and quantified using an enzyme-derivatization fluorescence technique. Primary calibration was performed using aqueous standards and known flow rates. Occasionally, CH2O gas standard additions to ambient air were performed as a secondary calibration. Analytical blanks were determined by replacing ambient air with pure air. The estimated precision was ±30 pptv and the estimated accuracy was the sum of ±30 parts per trillion by volume (pptv) ±15% of the measured value. Approximately 25% of the observations were less than the instrumental detection limit of 50 pptv, and 85% of these occurred above 6 km. CH2O mixing ratios decreased with altitude; for example, near the equator the median value in the lowest 2 km was 275 pptv, decreased to 150 pptv by 6 km and was below 100 pptv above 8 km. Between 130 and 170 W and below 1km, a small variation of CH2O mixing ratio with latitude was noted as near-surface median mixing ratios decreased near the equator (275 pptv) and were greater on either side (375 pptv). A marked decrease in near-surface CH2O (200 pptv) was noted south of 23° S on two flights. Between 3° and 23° S, median CH2O mixing ratios were lower in the eastern tropical Pacific than in the western or central Pacific; nominal differences were >100 pptv near the surface to ∼100 pptv at midaltitude to ∼50 pptv at high altitude. Off the coast of Central America and Mexico, mixing ratios as high as 1200 pptv were observed in plumes that originated to the east over land. CH2O observations were consistently higher than the results from a point model constrained by other photochemical species and meteorological parameters. Regardless of latitude or longitude, agreement was best at altitudes above 4 km where the difference between measured and modeled CH2O medians was less than 50 pptv. Below 2 km the model median was approximately 150 pptv less than the measured median. Copyright 2001 by the American Geophysical Union
A Comparison of Measured Crab and Vela Glitch Healing Parameters with Predictions of Neutron Star Models
There are currently two well-accepted models that explain how pulsars exhibit
glitches, sudden changes in their regular rotational spin-down. According to
the starquake model, the glitch healing parameter, Q, which is measurable in
some cases from pulsar timing, should be equal to the ratio of the moment of
inertia of the superfluid core of a neutron star (NS) to its total moment of
inertia. Measured values of the healing parameter from pulsar glitches can
therefore be used in combination with realistic NS structure models as one test
of the feasibility of the starquake model as a glitch mechanism. We have
constructed NS models using seven representative equations of state of
superdense matter to test whether starquakes can account for glitches observed
in the Crab and Vela pulsars, for which the most extensive and accurate glitch
data are available. We also present a compilation of all measured values of Q
for Crab and Vela glitches to date which have been separately published in the
literature. We have computed the fractional core moment of inertia for stellar
models covering a range of NS masses and find that for stable NSs in the
realistic mass range 1.4 +/- 0.2 solar masses, the fraction is greater than
0.55 in all cases. This range is not consistent with the observational
restriction Q < 0.2 for Vela if starquakes are the cause of its glitches. This
confirms results of previous studies of the Vela pulsar which have suggested
that starquakes are not a feasible mechanism for Vela glitches. The much larger
values of Q observed for Crab glitches (Q > 0.7) are consistent with the
starquake model predictions and support previous conclusions that starquakes
can be the cause of Crab glitches.Comment: 8 pages, including 3 figures and 1 table. Accepted for publication in
Ap
20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues
We present a series of new high-sensitivity and high-resolution
radio-continuum images of M31 at \lambda=20 cm (\nu=1.4 GHz). These new images
were produced by merging archived 20 cm radio-continuum observations from the
Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60
\mu Jy and feature high angular resolution (<10"). A complete sample of
discrete radio sources have been catalogued and analysed across 17 individual
VLA projects. We identified a total of 864 unique discrete radio sources across
the field of M31. One of the most prominent regions in M31 is the ring feature
for which we estimated total integrated flux of 706 mJy at \lambda=20 cm. We
compare here, detected sources to those listed in Gelfand et al. (2004) at
\lambda=92 cm and find 118 sources in common to both surveys. The majority
(61%) of these sources exhibit a spectral index of \alpha <-0.6 indicating that
their emission is predominantly non-thermal in nature. That is more typical for
background objects.Comment: 28 pages, 25 figures, accepted for publication in the Serbian
Astronomical Journa
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