33,312 research outputs found
Highlights from galactic observations with MAGIC
MAGIC is one of the main instruments for exploring the galactic gamma-ray sky
from ground in the energy range of 50 GeV - 50 TeV. It consists of two 17 m
diameter imaging atmospheric Cherenkov telescopes located at the Roque de los
Muchachos Observatory, on the Canary island of La Palma. Thanks to its
excellent sensitivity, MAGIC has conducted relevant studies on galactic objects
of different types at Very High Energies. Among them, the Crab pulsar up to TeV
energies, the spectral cut-off of the supernova remnant Cassiopeia A, the
super-orbital variability of the binary system LSI +61 303, the search for
microqusars, multi-year observations of the Galactic Center and follow-up
studies of unidentified HAWC sources. In many cases, the results from these
observations challenge our understanding of the underlying emission mechanisms.
Here we review the latest results from the observation of these galactic
sources with MAGIC.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea (arXiv:1708.05153
Robust phase retrieval with the swept approximate message passing (prSAMP) algorithm
In phase retrieval, the goal is to recover a complex signal from the
magnitude of its linear measurements. While many well-known algorithms
guarantee deterministic recovery of the unknown signal using i.i.d. random
measurement matrices, they suffer serious convergence issues some
ill-conditioned matrices. As an example, this happens in optical imagers using
binary intensity-only spatial light modulators to shape the input wavefront.
The problem of ill-conditioned measurement matrices has also been a topic of
interest for compressed sensing researchers during the past decade. In this
paper, using recent advances in generic compressed sensing, we propose a new
phase retrieval algorithm that well-adopts for both Gaussian i.i.d. and binary
matrices using both sparse and dense input signals. This algorithm is also
robust to the strong noise levels found in some imaging applications
Gravitational waves: search results, data analysis and parameter estimation
The Amaldi 10 Parallel Session C2 on gravitational wave (GW) search results, data analysis and parameter estimation included three lively sessions of lectures by 13 presenters, and 34 posters. The talks and posters covered a huge range of material, including results and analysis techniques for ground-based GW detectors, targeting anticipated signals from different astrophysical sources: compact binary inspiral, merger and ringdown; GW bursts from intermediate mass binary black hole mergers, cosmic string cusps, core-collapse supernovae, and other unmodeled sources; continuous waves from spinning neutron stars; and a stochastic GW background. There was considerable emphasis on Bayesian techniques for estimating the parameters of coalescing compact binary systems from the gravitational waveforms extracted from the data from the advanced detector network. This included methods to distinguish deviations of the signals from what is expected in the context of General Relativity
Proceedings of the second "international Traveling Workshop on Interactions between Sparse models and Technology" (iTWIST'14)
The implicit objective of the biennial "international - Traveling Workshop on
Interactions between Sparse models and Technology" (iTWIST) is to foster
collaboration between international scientific teams by disseminating ideas
through both specific oral/poster presentations and free discussions. For its
second edition, the iTWIST workshop took place in the medieval and picturesque
town of Namur in Belgium, from Wednesday August 27th till Friday August 29th,
2014. The workshop was conveniently located in "The Arsenal" building within
walking distance of both hotels and town center. iTWIST'14 has gathered about
70 international participants and has featured 9 invited talks, 10 oral
presentations, and 14 posters on the following themes, all related to the
theory, application and generalization of the "sparsity paradigm":
Sparsity-driven data sensing and processing; Union of low dimensional
subspaces; Beyond linear and convex inverse problem; Matrix/manifold/graph
sensing/processing; Blind inverse problems and dictionary learning; Sparsity
and computational neuroscience; Information theory, geometry and randomness;
Complexity/accuracy tradeoffs in numerical methods; Sparsity? What's next?;
Sparse machine learning and inference.Comment: 69 pages, 24 extended abstracts, iTWIST'14 website:
http://sites.google.com/site/itwist1
Towards optical intensity interferometry for high angular resolution stellar astrophysics
Most neighboring stars are still detected as point sources and are beyond the
angular resolution reach of current observatories. Methods to improve our
understanding of stars at high angular resolution are investigated. Air
Cherenkov telescopes (ACTs), primarily used for Gamma-ray astronomy, enable us
to increase our understanding of the circumstellar environment of a particular
system. When used as optical intensity interferometers, future ACT arrays will
allow us to detect stars as extended objects and image their surfaces at high
angular resolution.
Optical stellar intensity interferometry (SII) with ACT arrays, composed of
nearly 100 telescopes, will provide means to measure fundamental stellar
parameters and also open the possibility of model-independent imaging. A data
analysis algorithm is developed and permits the reconstruction of high angular
resolution images from simulated SII data. The capabilities and limitations of
future ACT arrays used for high angular resolution imaging are investigated via
Monte-Carlo simulations. Simple stellar objects as well as stellar surfaces
with localized hot or cool regions can be accurately imaged.
Finally, experimental efforts to measure intensity correlations are
expounded. The functionality of analog and digital correlators is demonstrated.
Intensity correlations have been measured for a simulated star emitting
pseudo-thermal light, resulting in angular diameter measurements. The StarBase
observatory, consisting of a pair of 3 m telescopes separated by 23 m, is
described.Comment: PhD dissertatio
A "nu" look at gravitational waves: The black hole birth rate from neutrinos combined with the merger rate from LIGO
We make projections for measuring the black hole birth rate from the diffuse
supernova neutrino background (DSNB) by future neutrino experiments, and
constrain the black hole merger fraction , when combined with
information on the black hole merger rate from gravitational wave experiments
such as LIGO. The DSNB originates from neutrinos emitted by all the supernovae
in the Universe, and is expected to be made up of two components: neutrinos
from neutron-star-forming supernovae, and a sub-dominant component at higher
energies from black-hole-forming "unnovae". We perform a Markov Chain Monte
Carlo analysis of simulated data of the DSNB in an experiment similar to
Hyper-Kamiokande, focusing on this second component. Since all knowledge of the
neutrino emission from unnovae comes from simulations of collapsing stars, we
choose two sets of priors: one where the unnovae are well-understood and one
where their neutrino emission is poorly known. By combining the black hole
birth rate from the DSNB with projected measurements of the black hole merger
rate from LIGO, we show that the fraction of black holes which lead to binary
mergers observed today could be constrained to be within the range
at confidence,
after ten years of running an experiment like Hyper-Kamiokande.Comment: 19 pages, 6 figures. v3: Matches version accepted to JCA
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