3,311 research outputs found
The Mock LISA Data Challenges: from Challenge 3 to Challenge 4
The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis
capabilities and to encourage their development. Each round of challenges
consists of one or more datasets containing simulated instrument noise and
gravitational waves from sources of undisclosed parameters. Participants
analyze the datasets and report best-fit solutions for the source parameters.
Here we present the results of the third challenge, issued in Apr 2008, which
demonstrated the positive recovery of signals from chirping Galactic binaries,
from spinning supermassive--black-hole binaries (with optimal SNRs between ~ 10
and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10-50), from
cosmic-string-cusp bursts (SNRs of 10-100), and from a relatively loud
isotropic background with Omega_gw(f) ~ 10^-11, slightly below the LISA
instrument noise.Comment: 12 pages, 2 figures, proceedings of the 8th Edoardo Amaldi Conference
on Gravitational Waves, New York, June 21-26, 200
The Mock LISA Data Challenges: from challenge 3 to challenge 4
The Mock LISA Data Challenges are a program to demonstrate LISA data-analysis capabilities and to encourage their development. Each round of challenges consists of one or more datasets containing simulated instrument noise and gravitational waves from sources of undisclosed parameters. Participants analyze the datasets and report best-fit solutions for the source parameters. Here we present the results of the third challenge, issued in April 2008, which demonstrated the positive recovery of signals from chirping galactic binaries, from spinning supermassive-black-hole binaries (with optimal SNRs between ~10 and 2000), from simultaneous extreme-mass-ratio inspirals (SNRs of 10–50), from cosmic-string-cusp bursts (SNRs of 10–100), and from a relatively loud isotropic background with Ω_(gw)(f) ~ 10^(−11), slightly below the LISA instrument noise
Detection of a Fully-resolved Compton Shoulder of the Iron K-alpha Line in the Chandra X-ray Spectrum of GX 301-2
We report the detection of a fully-resolved, Compton-scattered emission line
in the X-ray spectrum of the massive binary GX 301-2 obtained with the High
Energy Transmission Grating Spectrometer onboard the Chandra X-ray Observatory.
The iron K-alpha fluorescence line complex observed in this system consists of
an intense narrow component centered at an energy of E = 6.40 keV and a redward
shoulder that extends down to ~6.24 keV, which corresponds to an energy shift
of a Compton back-scattered iron K-alpha photon. From detailed Monte Carlo
simulations and comparisons with the observed spectra, we are able to directly
constrain the physical properties of the scattering medium, including the
electron temperature and column density, as well as an estimate for the metal
abundance.Comment: 13 pages, 4 figures, 1 table, accepted for publication in ApJ Lette
Filaments of the radio cosmic web: opportunities and challenges for SKA
The detection of the diffuse gas component of the cosmic web remains a
formidable challenge. In this work we study synchrotron emission from the
cosmic web with simulated SKA1 observations, which can represent an fundamental
probe of the warm-hot intergalactic medium. We investigate radio emission
originated by relativistic electrons accelerated by shocks surrounding cosmic
filaments, assuming diffusive shock acceleration and as a function of the
(unknown) large-scale magnetic fields. The detection of the brightest parts of
large () filaments of the cosmic web should be within reach of the
SKA1-LOW, if the magnetic field is at the level of a percent
equipartition with the thermal gas, corresponding to for the
most massive filaments in simulations. In the course of a 2-years survey with
SKA1-LOW, this will enable a first detection of the "tip of the iceberg" of the
radio cosmic web, and allow for the use of the SKA as a powerful tool to study
the origin of cosmic magnetism in large-scale structures. On the other hand,
the SKA1-MID and SKA1-SUR seem less suited for this science case at low
redshift (), owing to the missing short baselines and the
consequent lack of signal from the large-scale brightness fluctuations
associated with the filaments. In this case only very long exposures ( hr) may enable the detection of filament for field of view in
the SKA1-SUR PAF Band1.Comment: 10 pages, 4 figures, to appear in Proceedings of 'Advancing
Astrophysics with the SKA (AASKA14) - Cosmic Magnetism' Chapter
The Optimal Gravitational Lens Telescope
Given an observed gravitational lens mirage produced by a foreground
deflector (cf. galaxy, quasar, cluster,...), it is possible via numerical lens
inversion to retrieve the real source image, taking full advantage of the
magnifying power of the cosmic lens. This has been achieved in the past for
several remarkable gravitational lens systems. Instead, we propose here to
invert an observed multiply imaged source directly at the telescope using an
ad-hoc optical instrument which is described in the present paper. Compared to
the previous method, this should allow one to detect fainter source features as
well as to use such an optimal gravitational lens telescope to explore even
fainter objects located behind and near the lens. Laboratory and numerical
experiments illustrate this new approach
Bayesian optimisation for likelihood-free cosmological inference
Many cosmological models have only a finite number of parameters of interest,
but a very expensive data-generating process and an intractable likelihood
function. We address the problem of performing likelihood-free Bayesian
inference from such black-box simulation-based models, under the constraint of
a very limited simulation budget (typically a few thousand). To do so, we adopt
an approach based on the likelihood of an alternative parametric model.
Conventional approaches to approximate Bayesian computation such as
likelihood-free rejection sampling are impractical for the considered problem,
due to the lack of knowledge about how the parameters affect the discrepancy
between observed and simulated data. As a response, we make use of a strategy
previously developed in the machine learning literature (Bayesian optimisation
for likelihood-free inference, BOLFI), which combines Gaussian process
regression of the discrepancy to build a surrogate surface with Bayesian
optimisation to actively acquire training data. We extend the method by
deriving an acquisition function tailored for the purpose of minimising the
expected uncertainty in the approximate posterior density, in the parametric
approach. The resulting algorithm is applied to the problems of summarising
Gaussian signals and inferring cosmological parameters from the Joint
Lightcurve Analysis supernovae data. We show that the number of required
simulations is reduced by several orders of magnitude, and that the proposed
acquisition function produces more accurate posterior approximations, as
compared to common strategies.Comment: 16+9 pages, 12 figures. Matches PRD published version after minor
modification
Time-ordered data simulation and map-making for the PIXIE Fourier transform spectrometer
We develop a time-ordered data simulator and map-maker for the proposed PIXIE
Fourier transform spectrometer and use them to investigate the impact of
polarization leakage, imperfect collimation, elliptical beams, sub-pixel
effects, correlated noise and spectrometer mirror jitter on the PIXIE data
analysis. We find that PIXIE is robust to all of these effects, with the
exception of mirror jitter which could become the dominant source of noise in
the experiment if the jitter is not kept significantly below . Source code is available at https://github.com/amaurea/pixie.Comment: 27 pages, 15 figures. Accepted for publication in JCA
The InfraRed Imaging Spectrograph (IRIS) for TMT: latest science cases and simulations
The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared
Imaging Spectrograph) will complete its preliminary design phase in 2016. The
IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral
field spectrograph (IFS) and imager that are able to conduct simultaneous
diffraction-limited observations behind the advanced adaptive optics system
NFIRAOS. The IRIS science cases have continued to be developed and new science
studies have been investigated to aid in technical performance and design
requirements. In this development phase, the IRIS science team has paid
particular attention to the selection of filters, gratings, sensitivities of
the entire system, and science cases that will benefit from the parallel mode
of the IFS and imaging camera. We present new science cases for IRIS using the
latest end-to-end data simulator on the following topics: Solar System bodies,
the Galactic center, active galactic nuclei (AGN), and distant
gravitationally-lensed galaxies. We then briefly discuss the necessity of an
advanced data management system and data reduction pipeline.Comment: 15 pages, 7 figures, SPIE (2016) 9909-0
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