Entity

Time filter

Source Type


Liu K.,CNRS Nancay Radioastronomy Station | Liu K.,French National Center for Scientific Research | Liu K.,Max Planck Institute for Radio Astronomy | Eatough R.P.,Max Planck Institute for Radio Astronomy | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The anticipated discovery of a pulsar in orbit with a black hole is expected to provide a unique laboratory for black hole physics and gravity. In this context, the next generation of radio telescopes, like the Five-hundred-meter Aperture Spherical radio Telescope (FAST) and the Square Kilometre Array (SKA), with their unprecedented sensitivity, will play a key role. In this paper, we investigate the capability of future radio telescopes to probe the space-time of a black hole and test gravity theories by timing a pulsar orbiting a stellar-mass black hole (SBH). Based on mock data simulations, we show that a few years of timing observations of a sufficiently compact pulsar-SBH (PSR-SBH) system with future radio telescopes would allow precise measurements of the black hole mass and spin. A measurement precision of 1 per cent can be expected for the spin. Measuring the quadrupole moment of the black hole, needed to test general relativity's (GR's) no-hair theorem, requires extreme system configurations with compact orbits and a large SBH mass. Additionally, we show that a PSR-SBH system can lead to greatly improved constraints on alternative gravity theories even if they predict black holes (practically) identical to GR's. This is demonstrated for a specific class of scalar-tensor theories. Finally, we investigate the requirements for searching for PSR-SBH systems. It is shown that the high sensitivity of the next generation of radio telescopes is key for discovering compact PSR-SBH systems, as it will allow for sufficiently short survey integration times. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Johnson T.J.,National Academy of science | Johnson T.J.,U.S. Navy | Venter C.,North West University South Africa | Harding A.K.,NASA | And 12 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

Millisecond pulsars (MSPs) are a growing class of gamma-ray emitters. Pulsed gamma-ray signals have been detected from more than 40 MSPs with the Fermi Large Area Telescope (LAT). The wider radio beams and more compact magnetospheres of MSPs enable studies of emission geometries over a broader range of phase space than non-recycled radio-loud gamma-ray pulsars. We have modeled the gamma-ray light curves of 40 LAT-detected MSPs using geometric emission models assuming a vacuum retarded-dipole magnetic field. We modeled the radio profiles using a single-altitude hollow-cone beam, with a core component when indicated by polarimetry; however, for MSPs with gamma-ray and radio light curve peaks occurring at nearly the same rotational phase, we assume that the radio emission is co-located with the gamma rays and caustic in nature. The best-fit parameters and confidence intervals are determined using a maximum likelihood technique. We divide the light curves into three model classes, with gamma-ray peaks trailing (Class I), aligned (Class II), or leading (Class III) the radio peaks. Outer gap and slot gap (two-pole caustic) models best fit roughly equal numbers of Class I and II, while Class III are exclusively fit with pair-starved polar cap models. Distinguishing between the model classes based on typical derived parameters is difficult. We explore the evolution of the magnetic inclination angle with period and spin-down power, finding possible correlations. While the presence of significant off-peak emission can often be used as a discriminator between outer gap and slot gap models, a hybrid model may be needed. © 2014. The American Astronomical Society. All rights reserved. Source


Lehnert M.D.,CNRS Paris Institute of Astrophysics | Van Driel W.,University Paris Diderot | Van Driel W.,CNRS Nancay Radioastronomy Station | Minchin R.,National Astronomy and Ionosphere Center
Astronomy and Astrophysics | Year: 2016

Local galaxies with specific star-formation rates (star-formation rate per unit mass; sSFR - 0.2-10 Gyr-1) that are as high as distant galaxies (z ≈ 1-3), are very rich in Hi. Those with low stellar masses, M∗ = 108-9 M⊙, for example, have MHI/M∗ ≈ 5-30. Using continuity arguments, whereby the specific merger rate is hypothesized to be proportional to the specific star-formation rate, along with Hi gas mass measurements for local galaxies with high sSFR, we estimate that moderate-mass galaxies, M∗ = 109-10.5 M⊙, can acquire enough gas through minor mergers (stellar mass ratios ∼4-100) to sustain their star formation rates at z ∼ 2. The relative fraction of the gas accreted through minor mergers declines with increasing stellar mass, and for the most massive galaxies considered, M↠= 1010.5-11 M⊙, this accretion rate is insufficient to sustain their star formation. We checked our minor merger hypothesis at z = 0 using the same methodology, but now with relations for local normal galaxies, and find that minor mergers cannot account for their specific growth rates, in agreement with observations of Hi-rich satellites around nearby spirals. We discuss a number of attractive features, such as a natural downsizing effect, in using minor mergers with extended Hi disks to support star formation at high redshift. The answer to the question posed by the title, "Can galaxy growth be sustained through Hi-rich minor mergers?", is "maybe", but only for relatively low-mass galaxies and at high redshift. © 2016 ESO. Source


Martin L.,Ecole des Mines de Nantes | Martin L.,CNRS Nancay Radioastronomy Station
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2014

Our knowledge on ultra-high energy cosmic rays and their underlying sources and acceleration mechanisms is steadily improving thanks to the large observatories nowadays in operation. However the need for a next generation instrument is emerging from their experimental limitations and the scientific questions currently out of reach within a reasonable time line. Within this scope, the main features of the radio detection of extensive air showers are investigated and confronted to these challenging requirements. CODALEMA is the last experiment currently running in Europe dedicated to the cosmic ray detection using the observation of its induced radio electric field. The latest experimental upgrade and the synthesis of its operation features and the upcoming technical developments are presented. The main results of CODALEMA will be presented with special emphasis put on some of the new aspects of the data analysis offered by the CODALEMA3 autonomous station array. Finally, the opportunities provided by the Nançay observatory for efficient R&D activities and especially the upcoming technical developments are listed. © 2013 Elsevier B.V. All rights reserved. Source


Pickett J.S.,University of Iowa | Grison B.,ASCR Institute of Physics Prague | Omura Y.,Kyoto University | Engebretson M.J.,Augsburg College | And 9 more authors.
Geophysical Research Letters | Year: 2010

The Cluster spacecraft were favorably positioned on the nightside near the equatorial plasmapause of Earth at L ∼ 4.3 on 30 March 2002 to observe electromagnetic ion cyclotron (EMIC) rising tone emissions in association with Pc1 waves at 1.5 Hz. The EMIC rising tone emissions were found to be left-hand, circularly polarized, dispersive, and propagating away from the equator. Their burstiness and dispersion of ∼30s/Hz rising out of the 1.5 Hz Pc1 waves are consistent with their identification as EMIC triggered chorus emissions, the first to be reported through in situ observations near the plasmapause. Along with the expected H+ ring current ions seen at higher energies (>300 eV), lower energy ions (300 eV and less) were observed during the most intense EMIC triggered emission events. Nonlinear wave-particle interactions via cyclotron resonance between the ∼2-10 keV H+ ions with temperature anisotropy and the linearly-amplified Pc1 waves are suggested as a possible generation mechanism for the EMIC triggered emissions. Copyright © 2010 by the American Geophysical Union. Source

Discover hidden collaborations