2,837 research outputs found
The Transition between Nonorthogonal Polarization Modes in PSR B2016+28 at 1404 MHz
Polarization observations of the radio emission from PSR B2016+28 at 1404 MHz
reveal properties that are consistent with two, very different, interpretations
of the pulsar's viewing geometry. The pulsar's average polarization properties
show a rapid change in position angle (PA) near the pulse center, suggesting
that the observer's sightline nearly intersects the star's magnetic pole. But
single pulse, polarization observations of the pulsar show nearly orthogonal
modes of polarization following relatively flat and parallel PA trajectories
across the pulse, suggesting that the sightline is far from the pole.
Additionally, PA histograms reveal a "modal connecting bridge", of unknown
origin, joining the modal PA trajectories over much of the pulse and following
the rapid PA change shown in the average data. The nonorthogonality of
polarization modes is incorporated in a statistical model of radio polarization
to account for the deviations from mode orthogonality that are observed in the
pulsar. The model is used to interpret the rapid PA change and modal connecting
bridge as a longitudinally-resolved transition between modes of nonorthogonal
polarization. Thus, the modal PA trajectories are argued to reflect the
pulsar's true viewing geometry. This interpretation is consistent with the
pulsar's morphological classification, preserves the Radhakrishnan & Cooke
model of pulsar radio emission, and avoids the complication that the modal
connecting bridge might be produced by some other emission mechanism. The
statistical model's ability to simulate the rich variety of polarization
properties observed in the emission lends additional support to the model's
applicability and its underlying assumption that the polarization modes occur
simultaneously.Comment: Accepted for publication in Ap
The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper Belt
The New Horizons spacecraft’s encounter with the cold classical Kuiper Belt object (486958) Arrokoth (provisional designation 2014 MU₆₉) revealed a contact-binary planetesimal. We investigate how Arrokoth formed, finding it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing cloud of solid particles. The geometric alignment of the lobes indicates they were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly due to dynamical friction and collisions within the cloud or later gas drag. Arrokoth’s contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper Belt, so informs the accretion processes that operated in the early Solar System
Increasing the analysis rate of automatic analysers by subtractively correcting for specimen interaction
Self-aligned fabrication process for silicon quantum computer devices
We describe a fabrication process for devices with few quantum bits (qubits),
which are suitable for proof-of-principle demonstrations of silicon-based
quantum computation. The devices follow the Kane proposal to use the nuclear
spins of 31P donors in 28Si as qubits, controlled by metal surface gates and
measured using single electron transistors (SETs). The accurate registration of
31P donors to control gates and read-out SETs is achieved through the use of a
self-aligned process which incorporates electron beam patterning, ion
implantation and triple-angle shadow-mask metal evaporation
Coherently Dedispersed Polarimetry of Millisecond Pulsars
We present a large sample of high-precision, coherently-dedispersed
polarization profiles of millisecond pulsars (MSPs) at frequencies between 410
and 1414 MHz. These data include the first polarimetric observations of several
of the pulsars, and the first low-frequency polarization profiles for others.
Our observations support previous suggestions that the pulse shapes and
polarimetry of MSPs are more complex than those of their slower relatives. An
immediate conclusion is that polarimetry-based classification schemes proposed
for young pulsars are of only limited use when applied to millisecond pulsars.Comment: 28 pages, 10 figures. Text matches version that appeared in ApJS.
Full paper with high-resolution figures available at
ftp://ftp.jb.man.ac.uk/pub/psr/papers/msppolpton.ps.g
Profile instabilities of the millisecond pulsar PSR J1022+1001
We present evidence that the integrated profiles of some millisecond pulsars
exhibit severe changes that are inconsistent with the moding phenomenon as
known from slowly rotating pulsars. We study these profile instabilities in
particular for PSR J1022+1001 and show that they occur smoothly, exhibiting
longer time constants than those associated with moding. In addition, the
profile changes of this pulsar seem to be associated with a relatively
narrow-band variation of the pulse shape. Only parts of the integrated profile
participate in this process which suggests that the origin of this phenomenon
is intrinsic to the pulsar magnetosphere and unrelated to the interstellar
medium. A polarization study rules out profile changes due to geometrical
effects produced by any sort of precession. However, changes are observed in
the circularly polarized radiation component. In total we identify four
recycled pulsars which also exhibit instabilities in the total power or
polarization profiles due to an unknown phenomenon (PSRs J1022+1001,
J1730-2304, B1821-24, J2145-0750).
The consequences for high precision pulsar timing are discussed in view of
the standard assumption that the integrated profiles of millisecond pulsars are
stable. As a result we present a new method to determine pulse times-of-arrival
that involves an adjustment of relative component amplitudes of the template
profile. Applying this method to PSR J1022+1001, we obtain an improved timing
solution with a proper motion measurement of -17 \pm 2 mas/yr in ecliptic
longitude. Assuming a distance to the pulsar as inferred from the dispersion
measure this corresponds to an one-dimensional space velocity of 50 km/s.Comment: 29 pages, 12 figures, accepted for publication in Ap
Optimising partner notification outcomes for bacterial sexually transmitted infections: a deliberative process and consensus
Partner notification (PN) is an essential element of sexually transmitted infection (STI) control. It enables identification, treatment and advice for sexual contacts who may benefit from additional preventive interventions, such as HIV pre-exposure prophylaxis (PrEP). PN is most effective in reducing STI transmission in a population when it reaches individuals who are most likely to have a STI, and to engage in sexual behaviour that facilitates STI transmission, including having multiple and/or new sex partners. Outcomes of PN practice need to be measurable in order to inform standards. They need to address all five stages in the cascade of care: elicitation of partners, establishing contactable partners, notification, testing and treatment. In the United Kingdom, established outcome measures cover only the first three stages and do not take into account the type of sexual partnership. We report on an evidence-based process used to develop new PN outcomes and inform standards of care. We undertook a systematic literature review, evaluation of published information on types of sexual partnership, and a modified Delphi process to reach consensus. We propose six new PN outcome measures at five stages of the cascade, including stratification for sex partnership type. Our framework for PN outcome measurement has potential to contribute in other domains, notably Covid-19
Frequency dependence of orthogonal polarisation modes in pulsars
We have carried out a study of the orthogonal polarisation mode behaviour as
a function of frequency of 18 pulsars, using average pulsar data from the
European Pulsar Network (EPN). Assuming that the radiation consists of two 100%
polarised completely orthogonal superposed modes we separated these modes,
resulting in average pulse profiles of each mode at multiple frequencies for
each pulsar. Furthermore, we studied the frequency dependence of the relative
intensity of these modes. We found in many pulsars that the average pulse
profiles of the two modes differ in their dependence on frequency. In
particular, we found that pulse components that are dominated by one mode tend
to increase in intensity with increasing frequency with respect to the rest of
the profile.Comment: 31 pages, 24 figures, 1 table, accepted by A&A; added references in
introductio
The Heavy Photon Search beamline and its performance
The Heavy Photon Search (HPS) is an experiment to search for a hidden sector
photon, aka a heavy photon or dark photon, in fixed target electroproduction at
the Thomas Jefferson National Accelerator Facility (JLab). The HPS experiment
searches for the ee decay of the heavy photon with bump hunt and
detached vertex strategies using a compact, large acceptance forward
spectrometer, consisting of a silicon microstrip detector (SVT) for tracking
and vertexing, and a PbWO electromagnetic calorimeter for energy
measurement and fast triggering. To achieve large acceptance and good vertexing
resolution, the first layer of silicon detectors is placed just 10 cm
downstream of the target with the sensor edges only 500 m above and below
the beam. Placing the SVT in such close proximity to the beam puts stringent
requirements on the beam profile and beam position stability. As part of an
approved engineering run, HPS took data in 2015 and 2016 at 1.05 GeV and 2.3
GeV beam energies, respectively. This paper describes the beam line and its
performance during that data taking
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