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- Algaba, Juan-Carlos, et al.
(author)
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Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
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Research review (peer-reviewed)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
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| 2. |
- Campbell, Charles, et al.
(author)
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Bridging model and real catalysts: general discussion
- 2016
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In: Faraday Discussions. - 1359-6640 .- 1364-5498. ; 188, s. 565-589
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Journal article (other academic/artistic)abstract
- Charles Campbell opened the discussion of the paper by Hans-JoachimFreund: If you have a 3D gold particle and it spreads out to be a 2D particle whenyou adsorb CO2, it must gain energy stability. Did you estimate the energy changeof the overall process to do that?
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| 6. |
- Bossini, D., et al.
(author)
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Magnetoelectrics and multiferroics : theory, synthesis, characterisation, preliminary results and perspectives for all-optical manipulations
- 2023
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 56:27
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Research review (peer-reviewed)abstract
- Solid state compounds exhibiting multiple and coupled macroscopic orders, named multiferroics, represent a challenge for both theoretical and experimental modern condensed-matter physics. Spins and the electric polarisation in conventional magnetic and ferroelectric materials can be manipulated on their fundamental timescales, by means of femtosecond laser pulses. In view of the resounding success and popularity of the all-optical approach, it is only natural to wonder about the application of this scheme to study the intrinsic coupling between spins and charges in multiferroics. Deeply fundamental questions arise: can ultrashort laser pulses deterministically activate, enhance or suppress the magnetoelectric coupling on the femtosecond timescale? Can these processes be triggered in a fully coherent fashion, thus being unrestrained by any thermal load? Which mechanism of spin-charge coupling is most favourable to overcome these overarching and daunting challenges? This problem is interdisciplinary in nature, requiring contributions from materials science and condensed matter physics from both theoretical and experimental perspectives. High-quality materials suitable for optical investigations have to be identified, synthetized and characterised. General and valid models offer then a guide to the plethora of possible light-induced processes, resulting in the desired ultrafast multiferroic manipulations. Finally, healthy experimental schemes, able to unambiguously track the ultrafast dynamics of either the ferroelectric or the magnetic order parameter have to be developed and implemented. Our motivation to write this review is to lay a broad and multidisciplinary foundation, which may be employed as a starting point for non-equilibrium approaches to the manipulation of the multiferroicity on the femtosecond timescale. This was also one of the main goals of the COST Action MAGNETOFON, whose network constitutes the core of the authors of this review. The present work thus represents a part of the scientific legacy of MAGNETOFON itself.
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| 7. |
- Joffrin, E., et al.
(author)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
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In: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Research review (peer-reviewed)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 8. |
- Psaridi, A., et al.
(author)
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Discovery of two warm mini-Neptunes with contrasting densities orbiting the young K3V star TOI-815
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
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Journal article (peer-reviewed)abstract
- We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K–M binary system. Analysis of its spectra and rotation period reveal the star to be young, with an age of 200+−400200 Myr. TOI-815b has a 11.2-day period and a radius of 2.94 ± 0.05 R+ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62 ± 0.10 R+, based on observations of three nonconsecutive transits with TESS; targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6 ± 1.5 M+ (ρP = 1.64+−003331 g cm−3) and 23.5 ± 2.4 M+ (ρP = 7.2+−1110 g cm−3), respectively. Thus, the planets have very different masses, which is unusual for compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those undergoing strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere that constitutes a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3σ level. This emphasizes the peculiarity of the system’s orbital architecture, and probably hints at an eventful dynamical history.
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