221 research outputs found
Accelerating incoherent dedispersion
Incoherent dedispersion is a computationally intensive problem that appears
frequently in pulsar and transient astronomy. For current and future transient
pipelines, dedispersion can dominate the total execution time, meaning its
computational speed acts as a constraint on the quality and quantity of science
results. It is thus critical that the algorithm be able to take advantage of
trends in commodity computing hardware. With this goal in mind, we present
analysis of the 'direct', 'tree' and 'sub-band' dedispersion algorithms with
respect to their potential for efficient execution on modern graphics
processing units (GPUs). We find all three to be excellent candidates, and
proceed to describe implementations in C for CUDA using insight gained from the
analysis. Using recent CPU and GPU hardware, the transition to the GPU provides
a speed-up of 9x for the direct algorithm when compared to an optimised
quad-core CPU code. For realistic recent survey parameters, these speeds are
high enough that further optimisation is unnecessary to achieve real-time
processing. Where further speed-ups are desirable, we find that the tree and
sub-band algorithms are able to provide 3-7x better performance at the cost of
certain smearing, memory consumption and development time trade-offs. We finish
with a discussion of the implications of these results for future transient
surveys. Our GPU dedispersion code is publicly available as a C library at:
http://dedisp.googlecode.com/Comment: 15 pages, 4 figures, 2 tables, accepted for publication in MNRA
Discovery of 28 pulsars using new techniques for sorting pulsar candidates
Modern pulsar surveys produce many millions of candidate pulsars, far more
than can be individually inspected. Traditional methods for filtering these
candidates, based upon the signal-to-noise ratio of the detection, cannot
easily distinguish between interference signals and pulsars. We have developed
a new method of scoring candidates using a series of heuristics which test for
pulsar-like properties of the signal. This significantly increases the
sensitivity to weak pulsars and pulsars with periods close to interference
signals. By applying this and other techniques for ranking candidates from a
previous processing of the Parkes Multi-beam Pulsar Survey, 28 previously
unknown pulsars have been discovered. These include an eccentric binary system
and a young pulsar which is spatially coincident with a known supernova
remnant.Comment: To be published in Monthly Notices of the Royal Astronomical Society.
11 pages, 9 figure
Profile and polarization characteristics of energetic pulsars
In this paper we compare the characteristics of pulsars with a high spin-down
energy loss rate (Edot) against those with a low Edot. We show that the
differences in the total intensity pulse morphology between the two classes are
in general rather subtle. A much more significant difference is the fractional
polarization which is very high for high Edot pulsars and low for low Edot
pulsars. The Edot at the transition is very similar to the death line predicted
for curvature radiation. This suggests a possible link between high energy and
radio emission in pulsars and could imply that gamma-ray efficiency is
correlated with the degree of linear polarization in the radio band. The degree
of circular polarization is in general higher in the second component of
doubles, which is possibly caused by the effect of co-rotation on the curvature
of the field lines in the inertial observer frame.
The most direct link between the high energy emission and the radio emission
could be the sub-group of pulsars which we call the energetic wide beam
pulsars. These young pulsars have very wide profiles with steep edges and are
likely to be emitted from a single magnetic pole. The similarities with the
high energy profiles suggest that both types of emission are produced at the
same extended height range in the magnetosphere. Alternatively, the beams of
the energetic wide beam pulsars could be magnified by propagation effects in
the magnetosphere. This would naturally lead to decoupling of the wave modes,
which could explain the high degree of linear polarization. As part of this
study, we have discovered three previous unknown interpulse pulsars (and we
detected one for the first time at 20 cm). We also obtained rotation measures
for 18 pulsars whose values had not previously been measured.Comment: Corrected typo in pulsar name. 26 pages, 11 figures, accepted for
publication in MNRAS. Astro-ph version is missing 528 figures due to file
size restrictions. Please download complete paper from
http://www.atnf.csiro.au/people/pulsar/wj08b.pd
Selection of radio pulsar candidates using artificial neural networks
Radio pulsar surveys are producing many more pulsar candidates than can be
inspected by human experts in a practical length of time. Here we present a
technique to automatically identify credible pulsar candidates from pulsar
surveys using an artificial neural network. The technique has been applied to
candidates from a recent re-analysis of the Parkes multi-beam pulsar survey
resulting in the discovery of a previously unidentified pulsar.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society. 9 pages, 7 figures, and 1 tabl
The High Time Resolution Universe Pulsar Survey I: System configuration and initial discoveries
We have embarked on a survey for pulsars and fast transients using the
13-beam Multibeam receiver on the Parkes radio telescope. Installation of a
digital backend allows us to record 400 MHz of bandwidth for each beam, split
into 1024 channels and sampled every 64 us. Limits of the receiver package
restrict us to a 340 MHz observing band centred at 1352 MHz. The factor of
eight improvement in frequency resolution over previous multibeam surveys
allows us to probe deeper into the Galactic plane for short duration signals
such as the pulses from millisecond pulsars. We plan to survey the entire
southern sky in 42641 pointings, split into low, mid and high Galactic latitude
regions, with integration times of 4200, 540 and 270 s respectively.
Simulations suggest that we will discover 400 pulsars, of which 75 will be
millisecond pulsars. With ~30% of the mid-latitude survey complete, we have
re-detected 223 previously known pulsars and discovered 27 pulsars, 5 of which
are millisecond pulsars. The newly discovered millisecond pulsars tend to have
larger dispersion measures than those discovered in previous surveys, as
expected from the improved time and frequency resolution of our instrument.Comment: Updated author list. 10 pages, 7 figures. For publication in MNRA
Observations of radio pulses from CU Virginis
The magnetic chemically peculiar star CU Virginis is a unique astrophysical
laboratory for stellar magnetospheres and coherent emission processes. It is
the only known main sequence star to emit a radio pulse every rotation period.
Here we report on new observations of the CU Virginis pulse profile in the 13
and 20\,cm radio bands. The profile is known to be characterised by two peaks
of 100 circularly polarised emission that are thought to arise in an
electron-cyclotron maser mechanism. We find that the trailing peak is stable at
both 13 and 20\,cm, whereas the leading peak is intermittent at 13\,cm. Our
measured pulse arrival times confirm the discrepancy previously reported
between the putative stellar rotation rates measured with optical data and with
radio observations. We suggest that this period discrepancy might be caused by
an unknown companion or by instabilities in the emission region. Regular
long-term pulse timing and simultaneous multi-wavelength observations are
essential to clarify the behaviour of this emerging class of transient radio
source.Comment: Accepted by MNRAS Letters; 5 pages, 2 figures, 3 table
On the pulse--width statistics in radio pulsars. I. Importance of the interpulse emission
We performed Monte Carlo simulations of different properties of pulsar radio
emission, such as: pulsar periods, pulse-widths, inclination angles and rates
of occurrence of interpulse emission (IP). We used recently available large
data sets of the pulsar periods P, the pulse profile widths W and the magnetic
inclination angle alpha. We also compiled the largest ever database of pulsars
with interpulse emission, divided into the double-pole (DP-IP) and the
single-pole (SP-IP) cases. Their distribution on the P - Pdot diagram strongly
suggests a secular alignment of the magnetic axis from the originally random
orientation. We derived possible parent distribution functions of important
pulsar parameters by means of the Kolmogorov-Smirnov significance test using
the available data sets (P, W, alpha and IP), different models of pulsar radio
beam rho = rho(P) as well as different trial distribution functions of pulsar
period and the inclination angles. The best suited parent period distribution
function is the log-normal distribution, although the gamma function
distribution cannot be excluded. The strongest constraint on derived model
distribution functions was the requirement that the numbers of interpulses were
exactly (within 1sigma errors) at the observed level of occurrences. We found
that a suitable model distribution function for the inclination angle is the
complicated trigonometric function which has two local maxima, one near 0 deg
and the other near 90 deg. The former and the latter implies the right rates of
IP occurrence. It is very unlikely that the pulsar beam deviates significantly
from the circular cross-section. We found that the upper limit for the average
beaming factor fb describing a fraction of the full sphere (called also beaming
fraction) covered by a pulsar beam is about 10%. This implies that the number
of the neutron stars in the Galaxy might be underestimated.Comment: 35 pages, 18 figure
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