217 research outputs found
Radio Searches for Pulsars and Short-Duration Transients
I discuss methods and current software packages for radio searches for
pulsars and short-duration transients. I then describe the properties of the
current pulsar population and the status of and predictions for ongoing and
future surveys. The presently observed pulsar population numbers around 2000
and is expected to roughly double over the next five years, with the number of
millisecond pulsars expected to more than triple. Finally, I discuss individual
objects discovered in the Green Bank Telescope 350-MHz Drift-Scan Survey and
the Arecibo Pulsar ALFA Survey.Comment: 8 pages, 3 figures, submitted to the proceedings for the ASTRONS 2010
meetin
Detection of Dispersed Radio Pulses: A machine learning approach to candidate identification and classification
Searching for extraterrestrial, transient signals in astronomical data sets
is an active area of current research. However, machine learning techniques are
lacking in the literature concerning single-pulse detection. This paper
presents a new, two-stage approach for identifying and classifying dispersed
pulse groups (DPGs) in single-pulse search output. The first stage identified
DPGs and extracted features to characterize them using a new peak
identification algorithm which tracks sloping tendencies around local maxima in
plots of signal-to-noise ratio vs. dispersion measure. The second stage used
supervised machine learning to classify DPGs. We created four benchmark data
sets: one unbalanced and three balanced versions using three different
imbalance treatments.We empirically evaluated 48 classifiers by training and
testing binary and multiclass versions of six machine learning algorithms on
each of the four benchmark versions. While each classifier had advantages and
disadvantages, all classifiers with imbalance treatments had higher recall
values than those with unbalanced data, regardless of the machine learning
algorithm used. Based on the benchmarking results, we selected a subset of
classifiers to classify the full, unlabelled data set of over 1.5 million DPGs
identified in 42,405 observations made by the Green Bank Telescope. Overall,
the classifiers using a multiclass ensemble tree learner in combination with
two oversampling imbalance treatments were the most efficient; they identified
additional known pulsars not in the benchmark data set and provided six
potential discoveries, with significantly less false positives than the other
classifiers.Comment: 13 pages, accepted for publication in MNRAS, ref. MN-15-1713-MJ.R
Probing fundamental physics with pulsars
Pulsars provide a wealth of information about General Relativity, the
equation of state of superdense matter, relativistic particle acceleration in
high magnetic fields, the Galaxy's interstellar medium and magnetic field,
stellar and binary evolution, celestial mechanics, planetary physics and even
cosmology. The wide variety of physical applications currently being
investigated through studies of radio pulsars rely on: (i) finding interesting
objects to study via large-scale and targeted surveys; (ii) high-precision
timing measurements which exploit their remarkable clock-like stability. We
review current surveys and the principles of pulsar timing and highlight
progress made in the rotating radio transients, intermittent pulsars, tests of
relativity, understanding pulsar evolution, measuring neutron star masses and
the pulsar timing array.Comment: 6 pages, 1 figure, to appear in the proceedings of IAU XXVII GA - JD3
- Neutron Stars: Timing in Extreme Environments XXVII IAU General Assembly,
Rio de Janeiro, Brazil, 3-14 August 200
A Study of Single Pulses in the Parkes Multibeam Pulsar Survey
We reprocessed the Parkes Multibeam Pulsar Survey, searching for single
pulses out to a DM of 5000 pc cm with widths of up to one second. We
recorded single pulses from 264 known pulsars and 14 Rotating Radio Transients.
We produced amplitude distributions for each pulsar which we fit with
log-normal distributions, power-law tails, and a power-law function divided by
an exponential function, finding that some pulsars show a deviation from a
log-normal distribution in the form of an excess of high-energy pulses. We
found that a function consisting of a power-law divided by an exponential fit
the distributions of most pulsars better than either log-normal or power-law
functions. For pulsars that were detected in a periodicity search, we computed
the ratio of their single-pulse signal-to-noise ratios to their signal-to-noise
ratios from a Fourier transform and looked for correlations between this ratio
and physical parameters of the pulsars. The only correlation found is the
expected relationship between this ratio and the spin period. Fitting
log-normal distributions to the amplitudes of pulses from RRATs showed similar
behaviour for most RRATs. Here, however, there seem to be two distinct
distributions of pulses, with the lower-energy distribution being consistent
with noise. Pulse-energy distributions for two of the RRATS processed were
consistent with those found for normal pulsars, suggesting that pulsars and
RRATs have a common emission mechanism, but other factors influence the
specific emission properties of each source class.Comment: 11 pages, 6 figures, 3 tables, accepted for publication in MNRA
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