19,326 research outputs found
Versatile liquid helium scintillation counter of large volume design
Design and performance of large liquid helium scintillation counter for meson experiment
Electromagnetic emission from long-lived binary neutron star merger remnants II: lightcurves and spectra
Recent observations indicate that in a large fraction of binary neutron star (BNS) mergers a long-lived neutron star (NS) may be formed rather than a black hole. Unambiguous electromagnetic (EM) signatures of such a scenario would strongly impact our knowledge on how short gamma-ray bursts (SGRBs) and their afterglow radiation are generated. Furthermore, such EM signals would have profound implications for multimessenger astronomy with joint EM and gravitational-wave (GW) observations of BNS mergers, which will soon become reality with the ground-based advanced LIGO/Virgo GW detector network starting its first science run this year. Here we explore such EM signatures based on the model presented in a companion paper, which provides a self-consistent evolution of the post-merger system and its EM emission starting from an early baryonic wind phase and resulting in a final pulsar wind nebula that is confined by the previously ejected material. Lightcurves and spectra are computed for a wide range of post-merger physical properties and particular attention is paid to the emission in the X-ray band. In the context of SGRB afterglow modeling, we present X-ray lightcurves corresponding to the 'standard' and the recently proposed 'time-reversal' scenario (SGRB prompt emission produced at the time of merger or at the time of collapse of the long-lived NS). The resulting afterglow lightcurve morphologies include, in particular, single and two-plateau features with timescales and luminosities that are in good agreement with the observations by the Swift satellite. Furthermore, we compute the X-ray signal that should precede the SGRB in the time-reversal scenario. If found, such a signal would represent smoking-gun evidence for this scenario. Finally, we find a bright, highly isotropic EM transient signal peaking in the X-ray band ..
Magnetically-induced outflows from binary neutron star merger remnants
Recent observations by the Swift satellite have revealed long-lasting (), "plateau-like" X-ray afterglows in the vast majority of short gamma-ray bursts events. This has put forward the idea of a long-lived millisecond magnetar central engine being generated in a binary neutron star (BNS) merger and being responsible for the sustained energy injection over these timescales ("magnetar model"). We elaborate here on recent simulations that investigate the early evolution of such a merger remnant in general-relativistic magnetohydrodynamics. These simulations reveal very different conditions than those usually assumed for dipole spin-down emission in the magnetar model. In particular, the surrounding of the newly formed NS is polluted by baryons due to a dense, highly magnetized and isotropic wind from the stellar surface that is induced by magnetic field amplification in the interior of the star. The timescales and luminosities of this wind are compatible with early X-ray afterglows, such as the "extended emission". These isotropic winds are a generic feature of BNS merger remnants and thus represent an attractive alternative to current models of early X-ray afterglows. Further implications to BNS mergers and short gamma-ray bursts are discussed
High efficiency deterministic Josephson Vortex Ratchet
We investigate experimentally a Josephson vortex ratchet -- a fluxon in an
asymmetric periodic potential driven by a deterministic force with zero time
average. The highly asymmetric periodic potential is created in an underdamped
annular long Josephson junction by means of a current injector providing
efficiency of the device up to 91%. We measured the ratchet effect for driving
forces with different spectral content. For monochromatic high-frequency drive
the rectified voltage becomes quantized. At high driving frequencies we also
observe chaos, sub-harmonic dynamics and voltage reversal due to the inertial
mass of a fluxon.Comment: accepted by PRL. To see status click on
http://134.2.74.170:88/cnt/cond-mat_0506754.htm
Subcritical Superstrings
We introduce the Liouville mode into the Green-Schwarz superstring. Like
massive supersymmetry without central charges, there is no kappa symmetry.
However, the second-class constraints (and corresponding Wess-Zumino term)
remain, and can be solved by (twisted) chiral superspace in dimensions D=4 and
6. The matter conformal anomaly is c = 4-D < 1. It thus can be canceled for
physical dimensions by the usual Liouville methods, unlike the bosonic string
(for which the consistency condition is c = D <= 1).Comment: 9 pg., compressed postscript file (.ps.Z), other formats (.dvi, .ps,
.ps.Z, 8-bit .tex) available at
http://insti.physics.sunysb.edu/~siegel/preprints/ or at
ftp://max.physics.sunysb.edu/preprints/siege
Lie Superalgebra Stability and Branes
The algebra of the generators of translations in superspace is unstable, in
the sense that infinitesimal perturbations of its structure constants lead to
non-isomorphic algebras. We show how superspace extensions remedy this
situation (after arguing that remedy is indeed needed) and review the benefits
reaped in the description of branes of all kinds in the presence of the extra
dimensions.Comment: Talk given at the conference ``Brane New World and Non-commutative
Geometry'', held in Torino, October 2000. To appear in the proceedings by
World Scientific. 10 pages, 1 figur
Suppression of dissipation in Nb thin films with triangular antidot arrays by random removal of pinning sites
The depinning current Ic versus applied magnetic field B close to the
transition temperature Tc of Nb thin films with randomly diluted triangular
arrays of antidots is investigated. % Our experiments confirm essential
features in Ic(B) as predicted by Reichhardt and Olson Reichhardt [Phys.Rev. B
76, 094512 (2007)]. % We show that, by introducing disorder into periodic
pinning arrays, Ic can be enhanced. % In particular, for arrays with fixed
density n_p of antidots, an increase in dilution Pd induces an increase in Ic
and decrease of the flux-flow voltage for B>Bp=n_p Phi_0.Comment: 5 pages, 4 figure
Direct current superconducting quantum interferometers with asymmetric shunt resistors
We have investigated asymmetrically shunted Nb/Al-AlO/Nb direct current
(dc) superconducting quantum interference devices (SQUIDs). While keeping the
total resistance identical to a comparable symmetric SQUID with , we shunted only one of the two Josephson junctions with
. Simulations predict that the optimum energy resolution
and thus also the noise performance of such an asymmetric SQUID can
be 3--4 times better than that of its symmetric counterpart. Experiments at a
temperature of 4.2\,K yielded for an asymmetric
SQUID with an inductance of . For a comparable symmetric device
was achieved, confirming our simulation results.Comment: 5 pages, 4 figure
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