3,216 research outputs found
PSR J1453+1902 and the radio luminosities of solitary versus binary millisecond pulsars
We present 3 yr of timing observations for PSR J1453+1902, a 5.79-ms pulsar
discovered during a 430-MHz drift-scan survey with the Arecibo telescope. Our
observations show that PSR J1453+1902 is solitary and has a proper motion of
8(2) mas/yr. At the nominal distance of 1.2 kpc estimated from the pulsar's
dispersion measure, this corresponds to a transverse speed of 46(11) km/s,
typical of the millisecond pulsar population. We analyse the current sample of
55 millisecond pulsars in the Galactic disk and revisit the question of whether
the luminosities of isolated millisecond pulsars are different from their
binary counterparts. We demonstrate that the apparent differences in the
luminosity distributions seen in samples selected from 430-MHz surveys can be
explained by small-number statistics and observational selection biases. An
examination of the sample from 1400-MHz surveys shows no differences in the
distributions. The simplest conclusion from the current data is that the spin,
kinematic, spatial and luminosity distributions of isolated and binary
millisecond pulsars are consistent with a single homogeneous population.Comment: 8 pages, 5 figures and 3 tables, accepted for publication by MNRA
Can we see pulsars around Sgr A*? - The latest searches with the Effelsberg telescope
Radio pulsars in relativistic binary systems are unique tools to study the
curved space-time around massive compact objects. The discovery of a pulsar
closely orbiting the super-massive black hole at the centre of our Galaxy, Sgr
A*, would provide a superb test-bed for gravitational physics. To date, the
absence of any radio pulsar discoveries within a few arc minutes of Sgr A* has
been explained by one principal factor: extreme scattering of radio waves
caused by inhomogeneities in the ionized component of the interstellar medium
in the central 100 pc around Sgr A*. Scattering, which causes temporal
broadening of pulses, can only be mitigated by observing at higher frequencies.
Here we describe recent searches of the Galactic centre region performed at a
frequency of 18.95 GHz with the Effelsberg radio telescope.Comment: 3 pages, 2 figures, Proceedings of IAUS 291 "Neutron Stars and
Pulsars: Challenges and Opportunities after 80 years", 201
Probing vibrational modes in silica glass using inelastic neutron scattering with mass contrast
The effective vibrational density of states (VDOS) has been derived from inelastic neutron-scattering data, for isotopically substituted Si O 18 2 and Si O 16 2 glasses, to gain information about the relative contribution to the Si and O partial VDOS. This is a necessary point of comparison for vibrational mode analyses of molecular-dynamics models. The mass contrast has led to a measurable shift between vibrational mode frequencies in the effective VDOS of Si O 18 2 and Si O 16 2, which is well reproduced in an ab initio simulation. The vibrational band centered at 100.2 meV is confirmed to have significantly lower contribution from the oxygen partial VDOS, than the higher (150.3 and 135.8 meV) and lower energy bands (53.3 meV)
New Binary and Millisecond Pulsars from Arecibo Drift-Scan Searches
We discuss four recycled pulsars found in Arecibo drift-scan searches. PSR
J1944+0907 has a spin period of 5.2 ms and is isolated. The 5.8-ms pulsar
J1453+19 may have a low-mass companion. We discuss these pulsars in the context
of isolated millisecond pulsar formation and the minimum spin period of neutron
stars. The isolated 56-ms pulsar J0609+2130 is possibly the remnant of a
disrupted double neutron star binary. The 41-ms pulsar J1829+2456 is in a
relativistic orbit. Its companion is most likely another neutron star, making
this the eighth known double neutron star binary system.Comment: 6 pages, 3 figures, to appear in proceedings of Aspen Center for
Physics Conference on ``Binary Radio Pulsars'' Eds. F. Rasio and I. Stair
Discovery of 59ms Pulsations from 1RXS J141256.0+792204 (Calvera)
We report on a multi-wavelength study of the compact object candidate 1RXS
J141256.0+792204 (Calvera). Calvera was observed in the X-rays with XMM/EPIC
twice for a total exposure time of ~50 ks. The source spectrum is thermal and
well reproduced by a two component model composed of either two hydrogen
atmosphere models, or two blackbodies (kT_1~ 55/150 eV, kT_2~ 80/250 eV,
respectively, as measured at infinity). Evidence was found for an absorption
feature at ~0.65 keV; no power-law high-energy tail is statistically required.
Using pn and MOS data we discovered pulsations in the X-ray emission at a
period P=59.2 ms. The detection is highly significant (> 11 sigma), and
unambiguously confirms the neutron star nature of Calvera. The pulse profile is
nearly sinusoidal, with a pulsed fraction of ~18%. We looked for the timing
signature of Calvera in the Fermi Large Area Telescope (LAT) database and found
a significant (~5 sigma) pulsed signal at a period coincident with the X-ray
value. The gamma-ray timing analysis yielded a tight upper limit on the period
derivative, dP/dt < 5E-18 s/s (dE_rot/dt <1E33 erg/s, B<5E10 G for magneto-
dipolar spin-down). Radio searches at 1.36 GHz with the 100-m Effelsberg radio
telescope yielded negative results, with a deep upper limit on the pulsed flux
of 0.05 mJy. Diffuse, soft (< 1 keV) X-ray emission about 13' west of the
Calvera position is present both in our pointed observations and in archive
ROSAT all-sky survey images, but is unlikely associated with the X-ray pulsar.
Its spectrum is compatible with an old supernova remnant (SNR); no evidence for
diffuse emission in the radio and optical bands was found. The most likely
interpretations are that Calvera is either a central compact object escaped
from a SNR or a mildly recycled pulsar; in both cases the source would be the
first ever member of the class detected at gamma-ray energies.Comment: 20 pages, 15 figures and 4 tables. Accepted for publication in MNRA
XY checkerboard antiferromagnet in external field
Ordering by thermal fluctuations is studied for the classical XY
antiferromagnet on a checkerboard lattice in zero and finite magnetic fields by
means of analytical and Monte Carlo methods. The model exhibits a variety of
novel broken symmetries including states with nematic ordering in zero field
and with triatic order parameter at high fields.Comment: 6 page
Managing action research: the PEArL framework
The difficulty of managing and validating Action Research field studies has been widely discussed. Several different approaches to Action Research have emerged, and one of the most widely used models is Checklandâs FMA model, where a framework is provided to facilitate interested individuals in ârecoveringâ the route of the inquiry. In this paper, I argue that the FMA model is a valuable tool for planning the application of theoretical ideas in a practical situation, but that, as a guide to Action Research, it still fails to provide a sense of the manner in which an inquiry is undertaken. The PEArL mnemonic has been previously offered as a guide to facilitate researchers, participants, and those interested in gaining an appreciation of the manner in which an inquiry is conducted. In this paper, it is argued that applying the PEArL elements does not provide insight into the dynamic nature of collaborative inquiry. In order to gain a sense of the manner in which an inquiry was undertaken it is necessary to apply the PEArL mnemonic alongside a framework that facilitates the flow of the action research cycle. To illustrate the framework, an Action Research field study is described that was undertaken with residents and key workers in a shelter for the homeless, where the aim was to create a shared understanding of complex needs and support requirements
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