2,725 research outputs found
Early Advanced LIGO binary neutron-star sky localization and parameter estimation
2015 will see the first observations of Advanced LIGO and the start of the
gravitational-wave (GW) advanced-detector era. One of the most promising
sources for ground-based GW detectors are binary neutron-star (BNS)
coalescences. In order to use any detections for astrophysics, we must
understand the capabilities of our parameter-estimation analysis. By simulating
the GWs from an astrophysically motivated population of BNSs, we examine the
accuracy of parameter inferences in the early advanced-detector era. We find
that sky location, which is important for electromagnetic follow-up, can be
determined rapidly (~5 s), but that sky areas may be hundreds of square
degrees. The degeneracy between component mass and spin means there is
significant uncertainty for measurements of the individual masses and spins;
however, the chirp mass is well measured (typically better than 0.1%).Comment: 4 pages, 2 figures. Published in the proceedings of Amaldi 1
Modeling the Redshift Evolution of the Normal Galaxy X-ray Luminosity Function
Emission from X-ray binaries (XRBs) is a major component of the total X-ray
luminosity of normal galaxies, so X-ray studies of high redshift galaxies allow
us to probe the formation and evolution of X-ray binaries on very long
timescales. In this paper, we present results from large-scale population
synthesis models of binary populations in galaxies from z = 0 to 20. We use as
input into our modeling the Millennium II Cosmological Simulation and the
updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently
account for the star formation history (SFH) and metallicity evolution of each
galaxy. We run a grid of 192 models, varying all the parameters known from
previous studies to affect the evolution of XRBs. We use our models and
observationally derived prescriptions for hot gas emission to create
theoretical galaxy X-ray luminosity functions (XLFs) for several redshift bins.
Models with low CE efficiencies, a 50% twins mass ratio distribution, a steeper
IMF exponent, and high stellar wind mass loss rates best match observational
results from Tzanavaris & Georgantopoulos (2008), though they significantly
underproduce bright early-type and very bright (Lx > 10d41) late-type galaxies.
These discrepancies are likely caused by uncertainties in hot gas emission and
SFHs, AGN contamination, and a lack of dynamically formed Low-mass XRBs. In our
highest likelihood models, we find that hot gas emission dominates the emission
for most bright galaxies. We also find that the evolution of the normal galaxy
X-ray luminosity density out to z = 4 is driven largely by XRBs in galaxies
with X-ray luminosities between 10d40 and 10d41 erg/s.Comment: Accepted into ApJ, 17 pages, 3 tables, 7 figures. Text updated to
address referee's comment
Supplement: Going the Distance: Mapping Host Galaxies of LIGO and Virgo Sources in Three Dimensions Using Local Cosmography and Targeted Follow-up
This is a supplement to the Letter of Singer et al.
(https://arxiv.org/abs/1603.07333), in which we demonstrated a rapid algorithm
for obtaining joint 3D estimates of sky location and luminosity distance from
observations of binary neutron star mergers with Advanced LIGO and Virgo. We
argued that combining the reconstructed volumes with positions and redshifts of
possible host galaxies can provide large-aperture but small field of view
instruments with a manageable list of targets to search for optical or infrared
emission. In this Supplement, we document the new HEALPix-based file format for
3D localizations of gravitational-wave transients. We include Python sample
code to show the reader how to perform simple manipulations of the 3D sky maps
and extract ranked lists of likely host galaxies. Finally, we include
mathematical details of the rapid volume reconstruction algorithm.Comment: For associated data release, see
http://asd.gsfc.nasa.gov/Leo.Singer/going-the-distanc
Binary evolution with LOFT
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of very faint X-ray binaries,
orbital period distribution of black hole X-ray binaries and neutron star spin
up. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timing. (v2 few typos corrected
DC fault ride-through capability and STATCOM operation of a HVDC hybrid voltage source converter
HVDC transmission systems are becoming increasingly popular when compared to conventional AC transmission methods. HVDC voltage source converters (VSC) can offer advantages over traditional HVDC current source converter topologies; as such, it is expected that HVDC-VSCs will be further exploited with the growth of HVDC transmission. This paper presents the DC fault ride through capability and new STATCOM modes of operation for the recently published Alternate Arm Converter (AAC), intended for the HVDC market. Operation and fault ride through of the converter during a local terminal to terminal short circuit of the DC-Link is demonstrated; during the fault STATCOM operation is also demonstrated
Ultra-light hierarchical meta-materials on a body-centred cubic lattice
Modern fabrication techniques offer the freedom to design and manufacture structures with complex geometry on many lengthscales, offering many potential advantages. For example, fractal/hierarchical struts have been shown to be exceptionally strong and yet light (Rayneau-Kirkhope D. et al., Phys. Rev. Lett., 109 (2012) 204301). In this letter, we propose a new class of meta-material, constructed from fractal or hierarchical struts linking a specific set of lattice points. We present a mechanical analysis of this meta-material resulting from a body-centred cubic (BCC) lattice. We show that, through the use of hierarchy, the material usage follows an enhanced scaling relation, and both material property and overall efficiency can be optimised for a specific applied stress. Such a design has the potential of providing the next generation of lightweight, buckling-resistant meta-materials
Highly multimode memory in a crystal
We experimentally demonstrate the storage of 1060 temporal modes onto a
thulium-doped crystal using an atomic frequency comb (AFC). The comb covers
0.93 GHz defining the storage bandwidth. As compared to previous AFC
preparation methods (pulse sequences i.e. amplitude modulation), we only use
frequency modulation to produce the desired optical pumping spectrum. To ensure
an accurate spectrally selective optical pumping, the frequency modulated laser
is self-locked on the atomic comb. Our approach is general and should be
applicable to a wide range of rare-earth doped material in the context of
multimode quantum memory
Time evolution of a non-singular primordial black hole
There is growing notion that black holes may not contain curvature
singularities (and that indeed nature in general may abhor such spacetime
defects). This notion could have implications on our understanding of the
evolution of primordial black holes (PBHs) and possibly on their contribution
to cosmic energy. This paper discusses the evolution of a non-singular black
hole (NSBH) based on a recent model [1]. We begin with a study of the
thermodynamic process of the black hole in this model, and demonstrate the
existence of a maximum horizon temperature T_{max}, corresponding to a unique
mass value. At this mass value the specific heat capacity C changes signs to
positive and the body begins to lose its black hole characteristics. With no
loss of generality, the model is used to discuss the time evolution of a
primordial black hole (PBH), through the early radiation era of the universe to
present, under the assumption that PBHs are non-singular. In particular, we
track the evolution of two benchmark PBHs, namely the one radiating up to the
end of the cosmic radiation domination era, and the one stopping to radiate
currently, and in each case determine some useful features including the
initial mass m_{f} and the corresponding time of formation t_{f}. It is found
that along the evolutionary history of the universe the distribution of PBH
remnant masses (PBH-RM) PBH-RMs follows a power law. We believe such a result
can be a useful step in a study to establish current abundance of PBH-MRs.Comment: To appear in Int. J. Mod. Phys.
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