431 research outputs found
A Study of Giant Pulses from PSR J1824-2452A
We have searched for microsecond bursts of emission from millisecond pulsars
in the globular cluster M28 using the Parkes radio telescope. We detected a
total of 27 giant pulses from the known emitter PSR J1824-2452A. At wavelengths
around 20 cm the giant pulses are scatter-broadened to widths of around 2
microseconds and follow power-law statistics. The pulses occur in two narrow
phase-windows which correlate in phase with X-ray emission and trail the peaks
of the integrated radio pulse-components. Notably, the integrated radio
emission at these phase windows has a steeper spectral index than other
emission. The giant pulses exhibit a high degree of polarization, with many
being 100% elliptically polarized. Their position angles appear random.
Although the integrated emission of PSR J1824-2452A is relatively stable for
the frequencies and bandwidths observed, the intensities of individual giant
pulses vary considerably across our bands. Two pulses were detected at both
2700 and 3500 MHz. The narrower of the two pulses is 20 ns wide at 3500 MHz. At
2700 MHz this pulse has an inferred brightness temperature at maximum of 5 x
10^37 K. Our observations suggest the giant pulses of PSR J1824-2452A are
generated in the same part of the magnetosphere as X-ray emission through a
different emission process to that of ordinary pulses.Comment: Accepted by Ap
A Search for Sub-Millisecond Pulsars
We have conducted a search of 19 southern Galactic globular clusters for
sub-millisecond pulsars at 660 MHz with the Parkes 64-m radio telescope. To
minimize dispersion smearing we used the CPSR baseband recorder, which samples
the 20 MHz observing band at the Nyquist rate. By possessing a complete
description of the signal we could synthesize an optimal filterbank in
software, and in the case of globular clusters of known dispersion measure,
much of the dispersion could be removed using coherent techniques. This allowed
for very high time resolution (25.6 us in most cases), making our searches in
general sensitive to sub-millisecond pulsars with flux densities greater than
about 3 mJy at 50 cm. No new pulsars were discovered, placing important
constraints on the proportion of pulsars with very short spin periods in these
clusters.Comment: 8 pages, 3 figures, to appear in Ap
Pulsars in Globular Clusters with the SKA
Globular clusters are highly efficient radio pulsar factories. These pulsars
can be used as precision probes of the clusters' structure, gas content,
magnetic field, and formation history; some of them are also highly interesting
in their own right because they probe exotic stellar evolution scenarios as
well as the physics of dense matter, accretion, and gravity. Deep searches with
SKA1-MID and SKA1-LOW will plausibly double to triple the known population.
Such searches will only require one to a few tied-array beams, and can be done
during early commissioning of the telescope - before an all-sky pulsar survey
using hundreds to thousands of tied-array beams is feasible. With SKA2 it will
be possible to observe most of the active radio pulsars within a large fraction
of the Galactic globular clusters, an estimated population of 600 - 3700
observable pulsars (those beamed towards us). This rivals the total population
of millisecond pulsars that can be found in the Galactic field; fully
characterizing it will provide the best-possible physical laboratories as well
as a rich dynamical history of the Galactic globular cluster system.Comment: 15 pages, 5 figures, to be published in: "Advancing Astrophysics with
the Square Kilometre Array", Proceedings of Science, PoS(AASKA14)04
On the Eccentricities and Merger Rates of Double Neutron Star Binaries and the Creation of "Double Supernovae"
We demonstrate that a natural consequence of an asymmetric kick imparted to
neutron stars at birth is that the majority of double neutron star binaries
should possess highly eccentric orbits. This leads to greatly accelerated
orbital decay, due to the enormous increase in the emission of gravitational
radiation at periastron as originally demonstrated by Peters (1964). A uniform
distribution of kick velocities constrained to the orbital plane would result
in ~24% of surviving binaries coalescing at least 10,000 times faster than an
unperturbed circular system. Even if the planar kick constraint is lifted, ~6%
of bound systems still coalesce this rapidly. In a non-negligible fraction of
cases it may even be possible that the system could coalesce within 10 years of
the final supernova, resulting in what we might term a "double supernova''. For
systems resembling the progenitor of PSR J0737-3039A, this number is as high as
\~9% (in the planar kick model). Whether the kick velocity distribution extends
to the range required to achieve this is still unclear. We do know that the
observed population of binary pulsars has a deficit of highly eccentric systems
at small orbital periods. In contrast, the long-period systems favour large
eccentricities, as expected. We argue that this is because the short-period
highly eccentric systems have already coalesced and are thus selected against
by pulsar surveys. This effect needs to be taken into account when using the
scale-factor method to estimate the coalescence rate of double neutron star
binaries. We therefore assert that the coalesence rate of such binaries is
underestimated by a factor of several.Comment: 7 pages, 6 figures, submitted to Ap
Implications of the PSR 1257+12 Planetary System for Isolated Millisecond Pulsars
The first extrasolar planets were discovered in 1992 around the millisecond
pulsar PSR 1257+12. We show that recent developments in the study of accretion
onto magnetized stars, plus the existence of the innermost, moon-sized planet
in the PSR 1257+12 system, suggest that the pulsar was born with approximately
its current rotation frequency and magnetic moment. If so, this has important
implications for the formation and evolution of neutron star magnetic fields as
well as for the formation of planets around pulsars. In particular, it suggests
that some and perhaps all isolated millisecond pulsars may have been born with
high spin rates and low magnetic fields instead of having been recycled by
accretion.Comment: 17 pages including one figure, uses aaspp4, accepted by Ap
Determination of the geometry of the PSR B1913+16 system by geodetic precession
New observations of the binary pulsar B1913+16 are presented. Since 1978 the
leading component of the pulse profile has weakend dramatically by about 40%.
For the first time, a decrease in component separation is observed, consistent
with expectations of geodetic precession. Assuming the correctness of general
relativity and a circular hollow-cone like beam, a fully consistent model for
the system geometry is developed. The misalignment angle between pulsar spin
and orbital momentum is determined giving direct evidence for an asymmetric
kick during the second supernova explosion. It is argued that the orbital
inclination angle is 132\fdg8 (rather than 47\fdg2). A prediction of this
model is that PSR B1913+16 will not be observable anymore after the year 2025.Comment: 16 pages, incl. 5 figures, accepted for publication in Ap
Recycled Pulsars Discovered at High Radio Frequency
We present the timing parameters of nine pulsars discovered in a survey of
intermediate Galactic latitudes at 1400 MHz with the Parkes radio telescope.
Eight of these pulsars possess small pulse periods and period derivatives
thought to be indicative of ``recycling''. Six of the pulsars are in circular
binary systems, including two with relatively massive white dwarf companions.
We discuss the implications of these new systems for theories of binary
formation and evolution. One long-period pulsar (J1410-7404) has a moderately
weak magnetic field and an exceedingly narrow average pulse profile, similar to
other recycled pulsars.Comment: 9 pages, 4 figures. Accepted for publication in Ap
MeerTime - the MeerKAT Key Science Program on Pulsar Timing
The MeerKAT telescope represents an outstanding opportunity for radio pulsar
timing science with its unique combination of a large collecting area and
aperture efficiency (effective area 7500 m), system temperature
(K), high slew speeds (1-2 deg/s), large bandwidths (770 MHz at 20cm
wavelengths), southern hemisphere location (latitude ) and
ability to form up to four sub-arrays. The MeerTime project is a five-year
program on the MeerKAT array by an international consortium that will regularly
time over 1000 radio pulsars to perform tests of relativistic gravity, search
for the gravitational wave signature induced by supermassive black hole
binaries in the timing residuals of millisecond pulsars, explore the interiors
of neutron stars through a pulsar glitch monitoring programme, explore the
origin and evolution of binary pulsars, monitor the swarms of pulsars that
inhabit globular clusters and monitor radio magnetars. In addition to these
primary programmes, over 1000 pulsars will have their arrival times monitored
and the data made immediately public. The MeerTime pulsar backend comprises two
server-class machines each of which possess four Graphics Processing Units. Up
to four pulsars can be coherently dedispersed simultaneously up to dispersion
measures of over 1000 pc cm. All data will be provided in psrfits
format. The MeerTime backend will be capable of producing coherently
dedispersed filterbank data for timing multiple pulsars in the cores of
globular clusters that is useful for pulsar searches of tied array beams. All
MeerTime data will ultimately be made available for public use, and any
published results will include the arrival times and profiles used in the
results.Comment: 15 pages, MeerKAT Science: On the Pathway to the SKA, 25-27 May,
2016, Stellenbosch, South Africa, available at:
https://pos.sissa.it/277/011/pd
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