1,766 research outputs found
Discovery of Five New Pulsars in Archival Data
Reprocessing of the Parkes Multibeam Pulsar Survey has resulted in the
discovery of five previously unknown pulsars and several as-yet-unconfirmed
candidates. PSR J0922-52 has a period of 9.68 ms and a DM of 122.4 pc cm^-3.
PSR J1147-66 has a period of 3.72 ms and a DM of 133.8 pc cm^-3. PSR J1227-6208
has a period of 34.53 ms, a DM of 362.6 pc cm^-3, is in a 6.7 day binary orbit,
and was independently detected in an ongoing high-resolution Parkes survey by
Thornton et al. and also in independent processing by Einstein@Home volunteers.
PSR J1546-59 has a period of 7.80 ms and a DM of 168.3 pc cm^-3. PSR J1725-3853
is an isolated 4.79-ms pulsar with a DM of 158.2 pc cm^-3. These pulsars were
likely missed in earlier processing efforts due to their high DMs and short
periods and the large number of candidates that needed to be looked through.
These discoveries suggest that further pulsars are awaiting discovery in the
multibeam survey data.Comment: 12 pages, 2 figures, 2 tables, accepted to Ap
Gravitational wave background from rotating neutron stars
The background of gravitational waves produced by the ensemble of rotating
neutron stars (which includes pulsars, magnetars and gravitars) is
investigated. A formula for \Omega(f) (commonly used to quantify the
background) is derived, properly taking into account the time evolution of the
systems since their formation until the present day. Moreover, the formula
allows one to distinguish the different parts of the background: the
unresolvable (which forms a stochastic background) and the resolvable. Several
estimations of the background are obtained, for different assumptions on the
parameters that characterize neutron stars and their population. In particular,
different initial spin period distributions lead to very different results. For
one of the models, with slow initial spins, the detection of the background can
be rejected. However, other models do predict the detection of the background
by the future ground-based gravitational wave detector ET. A robust upper limit
for the background of rotating neutron stars is obtained; it does not exceed
the detection threshold of two cross-correlated Advanced LIGO interferometers.
If gravitars exist and constitute more than a few percent of the neutron star
population, then they produce an unresolvable background that could be detected
by ET. Under the most reasonable assumptions on the parameters characterizing a
neutron star, the background is too faint. Previous papers have suggested
neutron star models in which large magnetic fields (like the ones that
characterize magnetars) induce big deformations in the star, which produce a
stronger emission of gravitational radiation. Considering the most optimistic
(in terms of the detection of gravitational waves) of these models, an upper
limit for the background produced by magnetars is obtained; it could be
detected by ET, but not by BBO or DECIGO.Comment: 25 pages, 15 figure
Observations of 20 millisecond pulsars in 47 Tucanae at 20 cm
We have used a new observing system on the Parkes radio telescope to carry
out a series of pulsar observations of the globular cluster 47 Tucanae at 20-cm
wavelength. We detected all 11 previously known pulsars, and have discovered
nine others, all of which are millisecond pulsars in binary systems. We have
searched the data for relatively short orbital period systems, and found one
pulsar with an orbital period of 96 min, the shortest of any known radio
pulsar.
The increased rate of detections with the new system resulted in improved
estimates of the flux density of the previously known pulsars, determination of
the orbital parameters of one of them, and a coherent timing solution for
another one. Five of the pulsars now known in 47 Tucanae have orbital periods
of a few hours and implied companion masses of only ~ 0.03 Msun. Two of these
are eclipsed at some orbital phases, while three are seen at all phases at 20
cm but not always at lower frequencies. Four and possibly six of the other
binary systems have longer orbital periods and companion masses ~ 0.2 Msun,
with at least two of them having relatively large orbital eccentricities. All
20 pulsars have rotation periods in the range 2-8 ms.Comment: 15 pages, 6 embedded EPS figures, to be published in The
Astrophysical Journa
Arecibo timing and single-pulse observations of 17 pulsars
We report on timing and single-pulse observations of 17 pulsars discovered at
the Arecibo observatory. The highlights of our sample are the recycled pulsars
J1829+2456, J1944+0907 and the drifting subpulses observed in PSR J0815+0939.
For the double neutron star binary J1829+2456, in addition to improving upon
our existing measurement of relativistic periastron advance, we have now
measured the pulsar's spin period derivative. This new result sets an upper
limit on the transverse speed of 120 km/s and a lower limit on the
characteristic age of 12.4 Gyr. From our measurement of proper motion of the
isolated 5.2-ms pulsar J1944+0907, we infer a transverse speed of 188 +/- 65
km/s. This is higher than that of any other isolated millisecond pulsar. An
estimate of the speed, using interstellar scintillation, of 235 +/- 45 km/s
indicates that the scattering medium along the line of sight is non-uniform. We
discuss the drifting subpulses detected from three pulsars in the sample, in
particular the remarkable drifting subpulse properties of the 645-ms pulsar
J0815+0939. Drifting is observed in all four components of the pulse profile,
with the sense of drift varying among the different components. This unusual
`bi-drifting'' behaviour challenges standard explanations of the drifting
subpulse phenomenon.Comment: 9 pages, 6 figures. Accepted for publication in MNRA
A periodically active pulsar giving insight into magnetospheric physics
PSR B1931+24 (J1933+2421) behaves as an ordinary isolated radio pulsar during
active phases that are 5-10 days long. However, the radio emission switches off
in less than 10 seconds and remains undetectable for the next 25-35 days, then
it switches on again. This pattern repeats quasi-periodically. The origin of
this behaviour is unclear. Even more remarkably, the pulsar rotation slows down
50% faster when it is on than when it is off. This indicates a massive increase
in magnetospheric currents when the pulsar switches on, proving that pulsar
wind plays a substantial role in pulsar spin-down. This allows us, for the
first time, to estimate the currents in a pulsar magnetospheric during the
occurrence of radio emission.Comment: 12 pages, 2 figure
Design of an apparatus for testing aeroplane fabric at low temperature
Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1934.MIT Institute Archives copy bound with: Thompson, Ransom S. and Sylvester, Edmund Q. Current trend in automotive engine design (1934). MICROFICHE COPY AVAILABLE.by Lorimer C. West.B.S
Propagation of gravitational waves in multimetric gravity
We discuss the propagation of gravitational waves in a recently discussed
class of theories containing N >= 2 metric tensors and a corresponding number
of standard model copies. Using the formalism of gauge-invariant linear
perturbation theory we show that all gravitational waves propagate at the speed
of light. We then employ the Newman-Penrose formalism to show that two to six
polarizations of gravitational waves may exist, depending on the parameters
entering the equations of motion. This corresponds to E(2) representations N_2,
N_3, III_5 and II_6. We finally apply our general discussion to a recently
presented concrete multimetric gravity model and show that it is of class N_2,
i.e., it allows only two tensor polarizations, as it is the case for general
relativity. Our results provide the theoretical background for tests of
multimetric gravity theories using the upcoming gravitational wave experiments.Comment: 21 pages, no figures, journal versio
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