A5002624839- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Astrophysics and Star Formation Studies
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- High-pressure geophysics and materials
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Ionosphere and magnetosphere dynamics
- Astronomy and Astrophysical Research
- Magnetic confinement fusion research
- Geomagnetism and Paleomagnetism Studies
- Radio Wave Propagation Studies
- Geophysics and Gravity Measurements
- Mechanics and Biomechanics Studies
- Antenna Design and Optimization
- Particle Accelerators and Free-Electron Lasers
- Lightning and Electromagnetic Phenomena
- Particle accelerators and beam dynamics
- Spectroscopy and Laser Applications
- Superconducting and THz Device Technology
Centre National de la Recherche Scientifique
2012-2021
Université d'Orléans
2012-2021
Laboratoire de Physique et Chimie de l’Environnement et de l’Espace
2012-2021
Laboratoire Chimie de l'Environnement
2009-2021
Université Paris Sciences et Lettres
2021
Astrophysique, Instrumentation et Modélisation
1998-2016
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2000-2016
CEA Paris-Saclay
2000-2016
Centre de Gestion Scientifique
2012-2015
Netherlands Institute for Radio Astronomy
2014
Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is new interferometer operating in the lowest 4 octaves ionospheric "radio window": 10-240MHz, that will greatly facilitate observing pulsars at low frequencies. Through huge collecting area, long baselines, and flexible digital hardware, it expected LOFAR revolutionize astronomy frequencies visible from Earth. next-generation telescope pathfinder Square...
Faraday rotation measurements using the current and next generation of low-frequency radio telescopes will provide a powerful probe astronomical magnetic fields. However, achieving full potential these requires accurate removal time-variable ionospheric contribution. We present ionFR, code that calculates amount for specific epoch, geographic location, line-of-sight. ionFR uses number publicly available, GPS-derived total electron content maps most recent release International Geomagnetic...
Pulsars emit low-frequency radio waves through to high-energy gamma-rays that are generated anywhere from the surface out edges of magnetosphere. Detecting correlated mode changes in multi-wavelength emission is therefore key understanding physical relationship between these sites. Through simultaneous observations, we have detected synchronous switching and X-ray properties PSR B0943+10. When pulsar a sustained 'bright' mode, X-rays show only an un-pulsed, non-thermal component. Conversely,...
The aim of the LOFAR Epoch Reionization (EoR) project is to detect spectral fluctuations redshifted HI 21cm signal. This signal weaker by several orders magnitude than astrophysical foreground signals and hence, in order achieve this, very long integrations, accurate calibration for stations ionosphere reliable removal are essential. One prospective observing windows EoR will be centered at North Celestial Pole (NCP). We present results from observations NCP window using highband antenna...
Context. The LOw Frequency ARray (LOFAR) radio telescope is a giant digital phased array interferometer with multiple antennas distributed in Europe. It provides discrete sets of Fourier components the sky brightness. Recovering original brightness distribution aperture synthesis forms an inverse problem that can be solved by various deconvolution and minimization methods Aims. Recent papers have established clear link between nature interferometry measurement "compressed sensing" (CS)...
Models of the accretion disks Young Stellar Objects show that they should not be ionized at a few AU from star, and thus subject to MHD turbulence believed cause accretion. This has been suggested create "Dead Zone" where remains unexplained. Here we existence Dead Zone self-consistently creates density profile favorable Rossby Wave Instability Lovelace et al. (1999, ApJ, 513, 805). instability will sustain vortices in disk which could lead enhanced planet formation.
view Abstract Citations (128) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nonlinear Coupling of Galactic Spiral Modes Tagger, M. ; Sygnet, J. F. Athanassoula, E. Pellat, R. The authors have worked out the nonlinear coupling modes with different pattern speeds and propose that it explains some salient features recent galactic simulations. This mechanism may provide a new key for understanding long-term evolution spirals in galaxies....
<i>Context. <i/>The formation of vortices in accretion disks is high interest various astrophysical contexts, particular for planet or the compact objects. But despite numerous attempts it has thus far not been possible to produce strong fully three-dimensional simulations disks.<i>Aims. aim this paper present first 3D simulation a vortex, established across vertically stratified structure disk by Rossby wave instability.<i>Methods. <i/>Using ersatile advection code (VAC), we set up...
M87 is a giant elliptical galaxy located in the centre of Virgo cluster, which harbours supermassive black hole mass 6.4x10^9 M_sun, whose activity responsible for extended (80 kpc) radio lobes that surround galaxy. The energy generated by matter falling onto central ejected and transferred to intra-cluster medium via relativistic jet morphologically complex systems buoyant bubbles, rise towards edges halo. Here we present first observations made with new Low-Frequency Array (LOFAR) at...
The characteristic outer scale of turbulence and the ratio random to ordered components magnetic field are key parameters characterise in interstellar gas, which affects propagation cosmic rays within Galaxy. We provide new constraints those two parameters. use LOw Frequency ARray (LOFAR) image diffuse continuum emission Fan region at (l,b) (137.0,+7.0) 80"x70" resolution range [146,174] MHz. detect multi-scale fluctuations Galactic synchrotron compute their power spectrum. Applying...
Dispersion in the interstellar medium is a well known phenomenon that follows simple relationship, which has been used to predict time delay of dispersed radio pulses since late 1960s. We performed wide-band simultaneous observations four pulsars with LOFAR (at 40-190 MHz), 76-m Lovell Telescope 1400 MHz) and Effelsberg 100-m 8000 test accuracy dispersion law over broad frequency range. In this paper we present results these show accurate better than 1 part 100000 across our observing band....
We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz here report on first low-frequency fast-radio burst limit discovery of new pulsars. The survey, LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction northern sky, ~1.4 x 10^4 sq. deg, 1-hr dwell times. Each observation covered ~75 deg using 7 independent fields formed by incoherently summing high-band antenna fields. second Tied-Array (LOTAS), spanned ~600...
Aims. This paper discusses the spectral occupancy for performing radio astronomy with Low-Frequency Array (LOFAR), a focus on imaging observations.
This study aims to characterise the polarized foreground emission in ELAIS-N1 field and address its possible implications for extraction of cosmological 21-cm signal from Low-Frequency Array - Epoch Reionization (LOFAR-EoR) data. We use high band antennas LOFAR image this region RM-synthesis unravel structures at Galactic latitudes. The brightness temperature detected is on average 4 K intensity covers range -10 +13rad m^-2 Faraday depth. total polarization angle show a wide morphological...
The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2000 km, has the unique capability achieving sub-arcsecond resolution at frequencies below 200 MHz. However, it technically and logistically challenging process data this resolution. To date only a handful publications have exploited capability. Here we present calibration strategy that builds on previous high-resolution work LOFAR. It implemented in pipeline using mostly...
This Letter is devoted to the still open problem of evolution a three-dimensional coronal flux tube embedded in low-beta ideal plasma and having its footpoints twisted by slow photospheric motions. Such process has been simulated with recently developed magnetohydrodynamic code. In particular calculation reported here, system occupies large cubic box. The field initially potential, being generated an underlying horizontal dipole, it two vortices located on lower face {z = 0} box, both sides...
Abell 2256 is one of the best known examples a galaxy cluster hosting large-scale diffuse radio emission that unrelated to individual galaxies. It contains both giant halo and relic, as well number head-tail sources smaller steep-spectrum sources. The origin halos relics still being debated, but over last years it has become clear presence these closely related merger events. Here we present results from first LOFAR Low band antenna (LBA) observations between 18 67 MHz. To our knowledge,...
The low-frequency radio spectra of the hotspots within powerful galaxies can provide valuable information about physical processes operating at site jet termination. These are responsible for dissipation kinetic energy, particle acceleration, and magnetic-field generation. Here, we report new observations galaxy Cygnus A using Low Frequency Array (LOFAR) between 109 183 MHz, an angular resolution ∼3.5 arcsec. emission lobes is found to have a complex spectral index distribution, with...
Context. Observing Jupiter's synchrotron emission from the Earth remains today sole method to scrutinize distribution and dynamical behavior of ultra energetic electrons magnetically trapped around planet (because in-situ particle data are limited in inner magnetosphere). Aims. We perform first resolved low-frequency imaging with LOFAR at 127 MHz. The radiation comes low energy (~1-30 MeV) which map a broad region magnetosphere. Methods (see article for complete abstract) Results. images...