1,417 research outputs found
Evidence for chaotic behaviour in pulsar spin-down rates
We present evidence for chaotic dynamics within the spin-down rates of 17
pulsars originally presented by Lyne et al. Using techniques that allow us to
re-sample the original measurements without losing structural information, we
have searched for evidence of a strange attractor in the time series of
frequency derivatives for each of the 17 pulsars. We demonstrate the
effectiveness of our methods by applying them to a component of the Lorenz and
R\"ossler attractors that were sampled with similar cadence to the pulsar time
series. Our measurements of correlation dimension and Lyapunov exponent show
that the underlying behaviour appears to be driven by a strange attractor with
approximately three governing non-linear differential equations. This is
particularly apparent in the case of PSR B182811 where a correlation
dimension of 2.06\pm0.03 and a Lyapunov exponent of
inverse days were measured. These results provide an additional diagnostic for
testing future models of this behaviour.Comment: 15 pages, 18 figures, 2 tables, Accepted to MNRA
Timing of pulsars found in a deep Parkes multibeam survey
We have carried out a sensitive radio pulsar survey along the northern
Galactic plane ( and |b| \lapp 2^{\circ}) using
the Parkes 20-cm multibeam system. We observed each position for 70-min on two
separate epochs. Our analyses to date have so far resulted in the detection of
32 pulsars, of which 17 were previously unknown. Here we summarize the
observations and analysis and present the timing observations of 11 pulsars and
discovery parameters for a further 6 pulsars. We also present a timing solution
for the 166-ms bursting pulsar, PSR~J1938+2213, previously discovered during an
Arecibo drift-scan survey. Our survey data for this pulsar show that the
emission can be described by a steady pulse component with bursting emission,
which lasts for typically 20--25 pulse periods, superposed. Other new
discoveries are the young 80.1-ms pulsar PSR~J1935+2025 which exhibits a
significant amount of unmodeled low-frequency noise in its timing residuals,
and the 4.2-ms pulsar PSR~J1935+1726 which is in a low-mass binary system with
a 90.7-day circular orbit.Comment: 6 pages, 2 figures, accepted for publication in MNRA
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
On the detectability of extragalactic fast radio transients
Recent discoveries of highly dispersed millisecond radio bursts by Thornton
et al. in a survey with the Parkes radio telescope at 1.4 GHz point towards an
emerging population of sources at cosmological distances whose origin is
currently unclear. Here we demonstrate that the scattering effects at lower
radio frequencies are less than previously thought, and that the bursts could
be detectable at redshifts out to about in surveys below 1 GHz. Using a
source model in which the bursts are standard candles with bolometric
luminosities ergs/s uniformly distributed per unit
comoving volume, we derive an expression for the observed peak flux density as
a function of redshift and use this, together with the rate estimates found by
Thornton et al. to find an empirical relationship between event rate and
redshift probed by a given survey. The non-detection of any such events in
Arecibo 1.4 GHz survey data by Deneva et al., and the Allen Telescope Array
survey by Simeon et al. is consistent with our model. Ongoing surveys in the
1--2 GHz band should result in further discoveries. At lower frequencies,
assuming a typical radio spectral index , the predicted peak flux
densities are 10s of Jy. As a result, surveys of such a population with current
facilities would not necessarily be sensitivity limited and could be carried
out with small arrays to maximize the sky coverage. We predict that sources may
already be present in 350-MHz surveys with the Green Bank Telescope. Surveys at
150 MHz with 30 deg fields of view could detect one source per hour above
30 Jy.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS on 2013 July
25. Received 2013 July 24; in original form 2013 May 3
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
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
Lutz-Kelker bias in pulsar parallax measurements
Lutz & Kelker showed that parallax measurements are systematically
overestimated because they do not properly account for the larger volume of
space that is sampled at smaller parallax values. We apply their analysis to
neutron stars, incorporating the bias introduced by the intrinsic radio
luminosity function and a realistic Galactic population model for neutron
stars. We estimate the bias for all published neutron star parallax
measurements and find that measurements with less than ~95% certainty, are
likely to be significantly biased. Through inspection of historic parallax
measurements, we confirm the described effects in optical and radio
measurements, as well as in distance estimates based on interstellar dispersion
measures. The potential impact on future tests of relativistic gravity through
pulsar timing and on X-ray--based estimates of neutron star radii is briefly
discussed.Comment: 9 pages, 3 tables, 1 figure. Accepted for publication in MNRA
A bright millisecond radio burst of extragalactic origin
Pulsar surveys offer one of the few opportunities to monitor even a small
fraction (~0.00001) of the radio sky for impulsive burst-like events with
millisecond durations. In analysis of archival survey data, we have discovered
a 30-Jy dispersed burst of duration <5 ms located three degrees from the Small
Magellanic Cloud. The burst properties argue against a physical association
with our Galaxy or the Small Magellanic Cloud. Current models for the free
electron content in the Universe imply a distance to the burst of <1 Gpc No
further bursts are seen in 90-hr of additional observations, implying that it
was a singular event such as a supernova or coalescence of relativistic
objects. Hundreds of similar events could occur every day and act as insightful
cosmological probes.Comment: 18 pages, 4 figures. Accepted by Science. Published electronically
via Science Express on September 27, 200
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