4,829 research outputs found
Magnon spin Hall magnetoresistance of a gapped quantum paramagnet
Motivated by recent experimental work, we consider spin transport between a
normal metal and a gapped quantum paramagnet. We model the latter as the
magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We
evaluate the spin current mediated by the interface exchange coupling between
the ferromagnet and the adjacent normal metal. For the strongly interacting
magnons that we consider, this spin current gives rise to a spin Hall
magnetoresistance that strongly depends on the magnitude of the magnetic field,
rather than its direction. This Letter may motivate electrical detection of the
phases of quantum magnets and the incorporation of such materials into
spintronic devices.Comment: 5 pages, 5 figure
Discovery of the energetic pulsar J1747-2809 in the supernova remnant G0.9+0.1
The supernova remnant G0.9+0.1 has long been inferred to contain a central
energetic pulsar. In observations with the NRAO Green Bank Telescope at 2 GHz,
we have detected radio pulsations from PSR J1747-2809. The pulsar has a
rotation period of 52 ms, and a spin-down luminosity of 4.3e37 erg/s, the
second largest among known Galactic pulsars. With a dispersion measure of 1133
pc/cc, PSR J1747-2809 is distant, at ~13 kpc according to the NE2001 electron
density model, although it could be located as close as the Galactic center.
The pulse profile is greatly scatter-broadened at a frequency of 2 GHz, so that
it is effectively undetectable at 1.4 GHz, and is very faint, with
period-averaged flux density of 40 uJy at 2 GHz.Comment: minor changes from v1 - matches published versio
Quark-nova remnants IV: Application to radio emitting AXP transients
(Abridged) XTE J1810-197 and 1E 1547.0-5408 are two transient AXPs exhibiting
radio emission with unusual properties. In addition, their spin down rates
during outburst show opposite trends, which so far has no explanation. Here, we
extend our quark-nova model for AXPs to include transient AXPs, in which the
outbursts are caused by transient accretion events from a Keplerian (iron-rich)
degenerate ring. For a ring with inner and outer radii of 23.5 km and 26.5 km,
respectively, our model gives a good fit to the observed X-ray outburst from
XTE J1810-197 and the behavior of temperature, luminosity, and area of the two
X-ray blackbodies with time. The two blackbodies in our model are related to a
heat front (i.e. Bohm diffusion front) propagating along the ring's surface and
an accretion hot spot on the quark star surface. Radio pulsations in our model
are caused by dissipation at the light cylinder of magnetic bubbles, produced
near the ring during the X-ray outburst. The delay between X-ray peak emission
and radio emission in our model is related to the propagation time of these
bubbles to the light cylinder. We predict a ~1 year and ~1 month delay for XTE
J1810-197 and 1E 1547.0-5408, respectively. The observed flat spectrum, erratic
pulse profile, and the pulse duration are all explained in our model as a
result of X-point reconnection events induced by the dissipation of the bubbles
at the light cylinder. The spin down rate of the central quark star can either
increase or decrease depending on how the radial drift velocity of the magnetic
islands changes with distance from the central star. We suggest an evolutionary
connection between transient AXPs and typical AXPs in our model.Comment: 16 journal pages, 4 figures and 1 table [Version accepted for
publication in A&A
Timing of pulsars found in a deep Parkes multibeam survey
We have carried out a sensitive radio pulsar survey along the northern
Galactic plane ( and |b| \lapp 2^{\circ}) using
the Parkes 20-cm multibeam system. We observed each position for 70-min on two
separate epochs. Our analyses to date have so far resulted in the detection of
32 pulsars, of which 17 were previously unknown. Here we summarize the
observations and analysis and present the timing observations of 11 pulsars and
discovery parameters for a further 6 pulsars. We also present a timing solution
for the 166-ms bursting pulsar, PSR~J1938+2213, previously discovered during an
Arecibo drift-scan survey. Our survey data for this pulsar show that the
emission can be described by a steady pulse component with bursting emission,
which lasts for typically 20--25 pulse periods, superposed. Other new
discoveries are the young 80.1-ms pulsar PSR~J1935+2025 which exhibits a
significant amount of unmodeled low-frequency noise in its timing residuals,
and the 4.2-ms pulsar PSR~J1935+1726 which is in a low-mass binary system with
a 90.7-day circular orbit.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Text authorship identified using the dynamics of word co-occurrence networks
The identification of authorship in disputed documents still requires human
expertise, which is now unfeasible for many tasks owing to the large volumes of
text and authors in practical applications. In this study, we introduce a
methodology based on the dynamics of word co-occurrence networks representing
written texts to classify a corpus of 80 texts by 8 authors. The texts were
divided into sections with equal number of linguistic tokens, from which time
series were created for 12 topological metrics. The series were proven to be
stationary (p-value>0.05), which permits to use distribution moments as
learning attributes. With an optimized supervised learning procedure using a
Radial Basis Function Network, 68 out of 80 texts were correctly classified,
i.e. a remarkable 85% author matching success rate. Therefore, fluctuations in
purely dynamic network metrics were found to characterize authorship, thus
opening the way for the description of texts in terms of small evolving
networks. Moreover, the approach introduced allows for comparison of texts with
diverse characteristics in a simple, fast fashion
Heartbeat of the Mouse: a young radio pulsar associated with the axisymmetric nebula G359.23-0.82
We report the discovery of PSR J1747-2958, a radio pulsar with period P = 98
ms and dispersion measure DM = 101 pc/cc, in a deep observation with the Parkes
telescope of the axially-symmetric "Mouse" radio nebula (G359.23-0.82). Timing
measurements of the newly discovered pulsar reveal a characteristic age Pdt/2dP
= 25 kyr and spin-down luminosity dE/dt = 2.5e36 erg/s. The pulsar (timing)
position is consistent with that of the Mouse's "head". The distance derived
from the DM, ~2 kpc, is consistent with the Mouse's distance limit from HI
absorption, < 5.5 kpc. Also, the X-ray energetics of the Mouse are compatible
with being powered by the pulsar. Therefore we argue that PSR J1747-2958,
moving at supersonic speed through the local interstellar medium, powers this
unusual non-thermal nebula. The pulsar is a weak radio source, with
period-averaged flux density at 1374 MHz of 0.25 mJy and luminosity ~1 mJy
kpc^2.Comment: 6 pages, 2 figures, accepted for publication in ApJ Letter
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