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All-sky search for long-duration gravitational-wave transients in the first part of the fourth LIGO-Virgo-KAGRA Observing run
No full textInternational audienceWe present an all-sky search for long-duration gravitational waves (GWs) from the first part of the LIGO-Virgo-KAGRA fourth observing run (O4), called O4a and comprising data taken between 24 May 2023 and 16 January 2024. The GW signals targeted by this search are the so-called "long-duration" (> 1 s) transients expected from a variety of astrophysical processes, including non-axisymmetric deformations in magnetars or eccentric binary coalescences. We make minimal assumptions on the emitted GW waveforms in terms of morphologies and durations. Overall, our search targets signals with durations ~1-1000 s and frequency content in the range 16-2048 Hz. In the absence of significant detections, we report the sensitivity limits of our search in terms of root-sum-square signal amplitude (hrss) of reference waveforms. These limits improve upon the results from the third LIGO-Virgo-KAGRA observing run (O3) by about 30% on average. Moreover, this analysis demonstrates substantial progress in our ability to search for long-duration GW signals owing to enhancements in pipeline detection efficiencies. As detector sensitivities continue to advance and observational runs grow longer, unmodeled long-duration searches will increasingly be able to explore a range of compelling astrophysical scenarios involving neutron stars and black holes
150 years of ground-based solar instrumentation at Meudon observatory (1876-2026)
No full textCe document est la version ANGLAISE du document en françaishttps://cnrs.hal.science/hal-05466472The Sun has been observed through a telescope for four centuries. However, its study made a prodigious leap at the end of the nineteenth century with the appearance of photography and spectroscopy, then at the beginning of the following century with the invention of the coronagraph and monochromatic filters, and finally in the second half of the twentieth century with the advent of large ground-based telescopes and space exploration. This article retraces the main stages of solar instrumental developments in Meudon, from its foundation by Jules Janssen in 1876 to the present day, limited to ground-based or balloon instrumentation, designed in Meudon and installed there or in other places (Nançay, Pic du Midi, Canary Islands). The Meudon astronomers played a pioneering role in the history of solar physics through the experimentation of innovative techniques. After the golden age of inventions, came the time of large instruments, studied in Meudon but often installed in more favourable sites, and that of space, in a framework of international collaboration, but this is not discussed here
150 ans d’instrumentation solaire sol à l’Observatoire de Meudon (1876-2026)
No full textDocument d'histoire des sciences relatant 150 ans d'instrumentation pour l'observation du Soleil à l'observatoire de Meudon, section d'Astrophysique de l'observatoire de Paris, à l'occasion des 150 ans du site de Meudon en 2026Le Soleil est observé à la lunette depuis quatre siècles. Cependant, son étude a fait un bond prodigieux à la fin du XIX ème siècle avec l'apparition de la photographie et de la spectroscopie, puis au début du siècle suivant avec l'invention du coronographe et des filtres monochromatiques, et enfin dans la seconde moitié du XX ème avec l'avènement des grands télescopes au sol et de l'exploration spatiale. Cet article retrace les grandes étapes des développements instrumentaux solaires à Meudon, depuis sa fondation par Jules Janssen en 1876 jusqu'à nos jours, en se limitant à l'instrumentation sol ou ballon, conçue à Meudon et installée à Meudon ou en d'autres lieux (Nançay, Pic du Midi, Canaries). Les Meudonnais ont joué un rôle pionnier dans l'histoire de la physique solaire par l'expérimentation de techniques innovantes. Après l'âge d'or des inventions, vint le temps des grands instruments, étudiés à Meudon mais souvent installés dans des sites plus favorables, et celui du spatial, dans un cadre de collaboration internationale, mais que nous n'abordons pas ici
Cygnus X-3: A variable petaelectronvolt gamma-ray source
No full textInternational audienceWe report the discovery of variable -rays up to petaelectronvolt from Cygnus X-3, an iconic X-ray binary. The -ray signal was detected with a statistical significance of approximately 10 by the Large High Altitude Air Shower Observatory (LHAASO). Its intrinsic spectral energy distribution (SED), extending from 0.06 to 3.7 PeV, shows a pronounced rise toward 1 PeV after accounting for absorption by the cosmic microwave background radiation. The detected month-scale variability,together with a 3.2 evidence for orbital modulation, suggests that the PeV -rays originate within, or in close proximity to, the binary system itself. The observed energy spectrum and temporal modulation can be naturally explained by -ray production through photomeson processes in the innermost region of the relativistic jet, where protons need to be accelerated to tens of PeV energies
Unified and consistent structure growth measurements from joint ACT, SPT and CMB lensing
No full textInternational audienceWe present the tightest cosmic microwave background (CMB) lensing constraints to date on the growth of structure by combining CMB lensing measurements from the Atacama Cosmology Telescope (ACT), the South Pole Telescope (SPT) and \textit{Planck}. Each of these surveys individually provides lensing measurements with similarly high statistical power, achieving signal-to-noise ratios of approximately 40. The combined lensing bandpowers represent the most precise CMB lensing power spectrum measurement to date with a signal-to-noise ratio of 61 and an amplitude of with respect to the theory prediction from the best-fit CMB \textit{Planck}-ACT cosmology. The bandpowers from all three lensing datasets, analyzed jointly, yield a measurement of the parameter combination . Including Dark Energy Spectroscopic Instrument (DESI) Baryon Acoustic Oscillation (BAO) data improves the constraint on the amplitude of matter fluctuations to (a determination). When combining with uncalibrated supernovae from \texttt{Pantheon+}, we present a sound-horizon-independent estimate of . The joint lensing constraints on structure growth and present-day Hubble rate are fully consistent with a CDM model fit to the primary CMB data from \textit{Planck} and ACT. While the precise upper limit is sensitive to the choice of data and underlying model assumptions, when varying the neutrino mass sum within the cosmological model, the combination of primary CMB, BAO and CMB lensing drives the probable upper limit for the mass sum towards lower values, comparable to the minimum mass prior required by neutrino oscillation experiments
Stellar properties indicating the presence of hyperons in neutron stars
No full textInternational audienceWe describe distinctive stellar features indicating the presence of hyperons in neutron stars. A strongly negative curvature of the mass-radius relation R(M) is characteristic of hyperons, which can be determined from measurements of neutron stars with three different masses. Similarly, a reduced second derivative of the tidal deformability as function of mass points to hyperonic degrees of freedom in NS matter. The slopes of such curves R(M) and λ(M) can distinguish a hyperonic equation of state from purely nucleonic models if they appear increased (decreased for λ(M)) relative to the maximum mass of neutron stars
Euclid: An emulator for baryonic effects on the matter bispectrum
No full textInternational audienceThe Euclid mission and other next-generation large-scale structure surveys will enable high-precision measurements of the cosmic matter distribution. Understanding the impact of baryonic processes such as star formation and AGN feedback on matter clustering is crucial to ensure precise and unbiased cosmological inference. Most theoretical models of baryonic effects to date focus on two-point statistics, neglecting higher-order contributions. This work develops a fast and accurate emulator for baryonic effects on the matter bispectrum, a key non-Gaussian statistic in the nonlinear regime. We employ high-resolution -body simulations from the BACCO suite and apply a combination of cutting-edge techniques such as cosmology scaling and baryonification to efficiently span a large cosmological and astrophysical parameter space. A deep neural network is trained to emulate baryonic effects on the matter bispectrum measured in simulations, capturing modifications across various scales and redshifts relevant to Euclid. We validate the emulator accuracy and robustness using an analysis of \Euclid mock data, employing predictions from the state-of-the-art FLAMINGO hydrodynamical simulations. The emulator reproduces baryonic suppression in the bispectrum to better than 2 for the percentile across most triangle configurations for and ensures consistency between cosmological posteriors inferred from second- and third-order weak lensing statistics
High Energy Emission from the Galactic Center
No full textInternational audienceThe center of the Galaxy is a prominent source in X-rays and gamma-rays. The study of its high-energy (HE) emission is crucial in understanding the physical phenomena taking place in this dense and extreme environment, where the closest supermassive black hole (SMBH) to us, Sgr A*, is lurking nearly invisible, today, in most of the energy spectrum. These phenomena are probably common to other galactic nuclei and may explain the feedback processes between nuclear regions and galaxies, so important for the overall evolution of the Universe. The Galactic center HE emission is very complex and consists of both thermal and non thermal radiation produced by compact and extended sources, surrounded by more diffuse components. All these objects and media are interacting with each other in the narrow and dense Central Molecular Zone (CMZ). Some of them also show relevant extensions towards the Galactic poles, indicating energetic outflows that seem to link the center to the recently observed large Galactic polar structures. In spite of the fundamental advances obtained in the last twenty five years with the most sensitive X-ray and gamma-ray observatories, several questions remain open to investigations. We review here the main observational results and the open issues on the high-energy diagnostics of the Galactic nuclear activity, focusing on processes that take place in the CMZ, and in particular discussing the role of the present and past SMBH activities in powering this region and possibly the whole Galaxy
Evidence of an Extended Alfvén Wing System at Enceladus: Cassini's Multi‐Instrument Observations
No full textInternational audienceWe report in situ evidence for Enceladus' Alfvén wing system and its coupling with Saturn's ionosphere, based on multi-instrument observations from the Cassini spacecraft. Analysis of 36 events, including 13 from non-flyby paths, confirms the existence of a Main Alfvén Wing (MAW) current system generated at Enceladus, and associated Reflected Alfvén Wings (RAWs) occurring both at Saturn's ionosphere and on the density gradient of Enceladus' plasma torus, extending longitudinally to at least ∼ 120°(∼2,000 moon radii) downstream of the moon. Additionally, the observations reveal the systematic existence of a filamentation process of these large-scale Alfvénic perturbations (MAW and RAWs) during their propagation at any distance from their source. These findings demonstrate a more extensive electrodynamic coupling than previously reported for Enceladus and more generally for any moon-magnetosphere interaction. Moreover, the observation of energetic electron depletions and water-group ion signatures at longitudes even further from the moon supports the interpretation of an extended and persistent interaction region. These results highlight Enceladus' role in shaping Saturn's magnetospheric environment and underscore the importance of future missions to exhaustively analyze this type of complex interaction between a moon and a planet. Plain Language Summary Saturn's small icy moon Enceladus interacts with the planet's magnetic field, generating intermittent aurora in Saturn's upper atmosphere and electromagnetic waves that travel along invisible magnetic connections between them. During its 13-year mission, the Cassini spacecraft repeatedly crossed these magnetic field lines linked to Enceladus. We used data from several Cassini instruments to study how energy and particles move between the moon and Saturn. We detected wave activity characteristic of Alfvén waves (similar to vibrations on a string), forming as Saturn's magnetic field flows past Enceladus. Due to a complex system of reflection at both Saturn's ionosphere and the boundary of Enceladus' torus, these waves were found not only near the moon but also trailing far behind it, extending more than 504,000 km (over 2,000 times the moon's radius) behind it. This is the first time that Alfvén waves have been observed to be directly linked to the charged particles associated with Enceladus. This shows that Enceladus plays a much bigger role in shaping Saturn's space environment than previously thought, and reveals how moons can influence their host planet across vast distances
Constraints on gravitational waves from the 2024 Vela pulsar glitch
No full textInternational audienceAmong known neutron stars, the Vela pulsar is one of the best targets for gravitational-wave searches. It is also one of the most prolific in terms of glitches, sudden frequency changes in a pulsar's rotation. Such glitches could cause a variety of transient gravitational-wave signals. Here we search for signals associated with a Vela glitch on 29 April 2024 in data of the two LIGO detectors from the fourth LIGO--Virgo--KAGRA observing run. We search both for seconds-scale burst-like emission, primarily from fundamental (f-)mode oscillations, and for longer quasi-monochromatic transients up to four months in duration, primarily from quasi-static quadrupolar deformations. We find no significant detection candidates, but for the first time we set direct observational upper limits on gravitational strain amplitude that are stricter than what can be indirectly inferred from the overall glitch energy scale. We discuss the short- and long-duration observational constraints in the context of specific emission models. These results demonstrate the potential of gravitational-wave probes of glitching pulsars as detector sensitivity continues to improve