Search results for "Astrophysics - Instrumentation and Methods"
showing 10 items of 215 documents
New method to observe gravitational waves emitted by core collapse supernovae
2018
While gravitational waves have been detected from mergers of binary black holes and binary neutron stars, signals from core collapse supernovae, the most energetic explosions in the modern Universe, have not been detected yet. Here we present a new method to analyse the data of the LIGO, Virgo, and KAGRA network to enhance the detection efficiency of this category of signals. The method takes advantage of a peculiarity of the gravitational wave signal emitted in the core collapse supernova and it is based on a classification procedure of the time-frequency images of the network data performed by a convolutional neural network trained to perform the task to recognize the signal. We validate …
Total-variation methods for gravitational-wave denoising: Performance tests on Advanced LIGO data
2018
We assess total-variation methods to denoise gravitational-wave signals in real noise conditions, by injecting numerical-relativity waveforms from core-collapse supernovae and binary black hole mergers in data from the first observing run of Advanced LIGO. This work is an extension of our previous investigation where only Gaussian noise was used. Since the quality of the results depends on the regularization parameter of the model, we perform an heuristic search for the value that produces the best results. We discuss various approaches for the selection of this parameter, either based on the optimal, mean, or multiple values, and compare the results of the denoising upon these choices. Mor…
Toward early-warning detection of gravitational waves from compact binary coalescence
2012
Rapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from (CBC). We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.
Cosmic magnetic fields with masclet: an application to galaxy clusters
2020
We describe and test a new version of the adaptive mesh refinement (AMR) cosmological code MASCLET. The new version of the code includes all the ingredients of its previous version plus a description of the evolution of the magnetic field under the approximation of the ideal magneto-hydrodynamics (MHD). To preserve the divergence-free condition of MHD, the original divergence cleaning algorithm of Dedner et al. (2002) is implemented. We present a set of well-known 1D and 2D tests, such as several shock-tube problems, the fast rotor and the Orszag-Tang vortex. The performance of the code in all the tests is excellent with estimated median relative errors of $\nabla \cdot {\bf B}$ in the 2D t…
Unravelling cosmic velocity flows: a Helmholtz-Hodge decomposition algorithm for cosmological simulations
2021
In the context of intra-cluster medium turbulence, it is essential to be able to split the turbulent velocity field in a compressive and a solenoidal component. We describe and implement a new method for this aim, i.e., performing a Helmholtz-Hodge decomposition, in multi-grid, multi-resolution descriptions, focusing on (but not being restricted to) the outputs of AMR cosmological simulations. The method is based on solving elliptic equations for a scalar and a vector potential, from which the compressive and the solenoidal velocity fields, respectively, are derived through differentiation. These equations are addressed using a combination of Fourier (for the base grid) and iterative (for t…
On the Measurements of Numerical Viscosity and Resistivity in Eulerian MHD Codes
2016
We propose a simple ansatz for estimating the value of the numerical resistivity and the numerical viscosity of any Eulerian MHD code. We test this ansatz with the help of simulations of the propagation of (magneto)sonic waves, Alfven waves, and the tearing mode instability using the MHD code Aenus. By comparing the simu- lation results with analytical solutions of the resistive-viscous MHD equations and an empirical ansatz for the growth rate of tearing modes we measure the numerical viscosity and resistivity of Aenus. The comparison shows that the fast-magnetosonic speed and wavelength are the characteristic velocity and length, respectively, of the aforementioned (relatively simple) syst…
Novel signatures of dark matter in laser-interferometric gravitational-wave detectors
2019
Dark matter may induce apparent temporal variations in the physical "constants", including the electromagnetic fine-structure constant and fermion masses. In particular, a coherently oscillating classical dark-matter field may induce apparent oscillations of physical constants in time, while the passage of macroscopic dark-matter objects (such as topological defects) may induce apparent transient variations in the physical constants. In this paper, we point out several new signatures of the aforementioned types of dark matter that can arise due to the geometric asymmetry created by the beam-splitter in a two-arm laser interferometer. These new signatures include dark-matter-induced time-var…
Magnetic shielding of soft protons in future X-ray telescopes: the case of the ATHENA Wide Field Imager
2018
Both the interplanetary space and the Earth magnetosphere are populated by low energy ($\leq300$ keV) protons that are potentially able to scatter on the reflecting surface of Wolter-I optics of X-ray focusing telescopes and reach the focal plane. This phenomenon, depending on the X-ray instrumentation, can dramatically increase the background level, reducing the sensitivity or, in the most extreme cases, compromising the observation itself. The use of a magnetic diverter, deflecting protons away from the field of view, requires a detailed characterization of their angular and energy distribution when exiting the mirror. We present the first end-to-end Geant4 simulation of proton scattering…
OCTOCAM: A fast multichannel imager and spectrograph for the 10.4m GTC
2010
OCTOCAM is a multi-channel imager and spectrograph that has been proposed for the 10.4m GTC telescope. It will use dichroics to split the incoming light to produce simultaneous observations in 8 different bands, ranging from the ultraviolet to the near-infrared. The imaging mode will have a field of view of 2' x 2' in u, g, r, i, z, J, H and Ks bands, whereas the long-slit spectroscopic mode will cover the complete range from 4,000 to 23,000 {\AA} with a resolution of 700 - 1,700 (depending on the arm and slit width). An additional mode, using an image slicer, will deliver a spectral resolution of over 3,000. As a further feature, it will use state of the art detectors to reach high readout…
Denoising of gravitational wave signals via dictionary learning algorithms
2016
Gravitational wave astronomy has become a reality after the historical detections accomplished during the first observing run of the two advanced LIGO detectors. In the following years, the number of detections is expected to increase significantly with the full commissioning of the advanced LIGO, advanced Virgo and KAGRA detectors. The development of sophisticated data analysis techniques to improve the opportunities of detection for low signal-to-noise-ratio events is, hence, a most crucial effort. In this paper, we present one such technique, dictionary-learning algorithms, which have been extensively developed in the last few years and successfully applied mostly in the context of image…