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Bright Cosmic-Ray Source as a Solution to Auger-TA Tensions
No full textInternational audienceThe ultra-high-energy cosmic ray (UHECR) spectra measured by the Pierre Auger Observatory (Auger) and the Telescope Array (TA) agree very well below eV but differ significantly at higher energies. We show that these differences can be explained by a single nearby source superimposed on a nearly isotropic background. Taking into account deflections in Galactic and extragalactic magnetic fields, such a source can account for the excess in the TA spectrum without producing excessive anisotropy. The required hard spectrum of the source and intermediate-mass composition are consistent with previous fits of the Auger-only spectrum and composition. This scenario offers several additional advantages: (i) the source produces a broad excess partially overlapping the TA hotspots, suggesting their possible explanation; (ii) without additional tuning, it reproduces the shift in dipole direction observed between the Auger-only and combined Auger-TA analyses; and (iii) the best-fit position of the source lies near M82, the brightest nearby starburst galaxy, making it a plausible source of the UHECR
Search for steady and flaring neutrino emission from cosmic sources using the complete ANTARES dataset
No full textInternational audienceANTARES, a neutrino detector located in the depths of the Mediterranean Sea, operated successfully for over 15 years before being decommissioned in 2022. The telescope offered an ideal vantage view of the Southern Sky and benefited from optimal water properties for enhanced angular resolution. This study makes use of data collected over the entire operational period of ANTARES to search for sources of high-energy cosmic neutrinos, considering both steady and flaring emission scenarios. First, a time-integrated search for high-energy neutrino clustering across the celestial sphere is conducted. The most significant accumulation is found at coordinates with a post-trial p-value equal to 0.38. A dedicated search in the Galactic Plane is also performed for extended sources, yielding no significant excess. Additionally, a list of potential neutrino sources are investigated. The blazar MG3 J225517+2409 is identified as the most significant object, yet the excess remains compatible with background fluctuations. A mild local excess of 2.4 is found for the blazar TXS 0506+056. The full sky is also examined for the presence of flaring neutrino emissions. The most significant excess in this case corresponds to a 4-day flare from the direction , with a post-trial p-value of 0.30. Finally, the directions of sources highlighted in IceCube's time-dependent searches are investigated. Temporal overlaps between ANTARES and IceCube flares are identified for PKS 1502+106 and TXS 0506+056, with an estimated chance probability of about 0.02%, making this observation particularly noteworthy
A novel double-rim forebaffle design for centimeter to sub-millimeter astrophysical observations
No full textInternational audienceStray radiation of various origin is a major source of degradation of centimeter to sub-millimeter astronomical observations. This is particularly problematic for the detection of signals such as faint cosmic microwave background polarization B modes, or for mapping large-scale extragalactic or Galactic diffuse emission. In this paper, we propose a double-rim forebaffle design to reduce the impact of such stray radiation contamination. Using qualitative arguments and numerical simulations, we show that such a design has the potential to substantially improve the quality of future observations
Identifying rocky planets and water worlds among sub-Neptune-sized exoplanets with the Habitable Worlds Observatory
No full textInternational audienceHabitable Worlds Observatory (HWO) Science Case Development Document (SCDD), presented at the "Towards the Habitable Worlds Observatory: Visionary Science and Transformational Technology" conference in July 2025, and to be published in the conference proceeding
Forward modelling of passive microwave emissivities over snow-covered areas at continental scale
No full textInternational audienceTo assimilate passive microwave data in numerical weather prediction, a comprehensive understanding of the components of the radiative transfer equation is essential. Given the significant variability of emissivity in snow-covered regions — affected by frequency, polarisation, and the macro- and microstructural properties of snow — attention must be paid to the design of a forward model. However, existing physical models are unsuitable for global-scale studies due to their reliance on numerous inputs, such as snow grain size across different layers, which are typically unavailable at larger scales. In this study, we propose a method that utilises geophysical properties accessible at the continental scale to derive accurate emissivity values for frequencies ranging from 1 GHz to 90 GHz, in both vertical and horizontal polarisations, with a focus on the incident angles of conical scanners (approximately 50°). Our approach employs neural networks to obtain a robust forward model using geophysical variables as input data. A training dataset was developed based on satellite-derived surface emissivity from the SMOS and AMSR2 instruments by subtracting atmospheric components and surface temperature modulation. The results, which accounts for the actual geophysical state of the surface and its temporal variability, outperform the emissivity climatologies. We achieved snow-covered surface emissivities at the continental scale with a correlation coefficient above 0.9 and a RMSE below 0.02 for frequencies up to 18.7 GHz, and around 0.03 for higher frequencies. Additionally, we demonstrate that, in a typical tundra snowpack where the macro- and microstructural properties of snow can be obtained, the emissivities retrieved by our neural network-based forward model are consistent with results from the physical model (SMRT). This proposed model will also support preparations for the CIMR mission
Measuring short range stray electric fields with a force quantum sensor
No full textInternational audienceWe use a quantum sensor based on trapped atom interferometry, and designed for probing short range atom-surface interactions, to characterize parasitic electric fields produced by adsorbed atoms or surface charges on a dielectric mirror. Applying controlled external fields with in-situ electrodes allows measuring electric field gradients with a relative uncertainty of order of 1% via variations of the force induced onto the atoms. More, our sensor can also be configured as a trapped microwave clock, allowing for direct measurements of the electric field amplitude via the Stark shift of the hyperfine transition frequency. Such measurements of the electric field amplitudes and gradients as a function of the atom-surface distance can be used to construct a model for the spatial distribution of the atoms adsorbed onto the surface of the mirror, and to accurately correct local force measurements, such as related to the Casimir–Polder interaction, from the detrimental impact of adsorbed atoms or stray charges.Nous utilisons un capteur quantique basé sur l’interférométrie à atomes piégés, et conçu pour sonder les interactions atomes-surface à courte distance, pour caractériser les champs électriques parasites produits par des atomes adsorbés ou des charges de surface sur un miroir diélectrique. L’application à l’aide d’électrodes in situ de champs externes contrôlés permet de mesurer les gradients de champ électrique avec une incertitude relative de l’ordre de 1 % grâce aux variations de la force induite sur les atomes. En outre, notre capteur peut également être configuré comme une horloge micro-onde piégée, ce qui permet de mesurer directement l’amplitude du champ électrique par le biais du décalage Stark de la fréquence de la transition hyperfine. Ces mesures des amplitudes et des gradients du champ électrique en fonction de la distance atomes-surface peuvent être utilisées pour construire un modèle de distribution spatiale des atomes adsorbés sur la surface du miroir et pour corriger avec précision les mesures de force locale, telles que celles liées à l’interaction Casimir–Polder, de l’impact préjudiciable d’atomes adsorbés ou de charges parasites
2D fully kinetic simulations of dayside magnetic reconnection in the presence of cold ions and a moderate guide field.
No full textInternational audienceThe standard conditions considered for magnetic reconnection to occur are usually antiparallel magnetic field configurations with a shear angle of 180◦. Reconnection is often observed with an additional out-of-plane component of the magnetic field (guide field). We performed two sets of 2D fully kinetic simulations using SMILEI code of asymmetric reconnection. The first set was performed initially by Dargent et al., 2017 with and without cold ions. While the second set with and without cold ions each conducted in the presence of a moderate guide field. The simulation domain size is set to (xmax , ymax) = (320, 128) di, enabling us to study these effects in the electron diffusion region (EDR) as well as the coupling across different scales, including ion diffusion region (IDR), outflow jets, and extended separatrices far from diffusion region. When the density gradient is combined with a guide field component at the magnetopause, it was suggested by Swisdak et al., 2003 that the electron diamagnetic drift governs the motion of the X-line.Our simulations reveal the development of an asymmetry in the reconnection plane as expected and a motion of the X-line in the opposite direction of the electron diamagnetic drift. This finding challenges the previously proposed explanation. We also report our progress in investigating the impact of cold ions in reinforcing the electron dynamics and further investigate the impact of adding a moderate guide field in their presence. These effects are expected to influence the energization, energy partitioning across scales, and potentially the suppression of reconnection. Fluid scales coupling with smaller ion scales aligns with the primary objective of the Plasma Observatory (PO) mission which aims to study plasma energization and energy transport. Our findings will contribute to the preparation of the PO mission and aim at improving its science return
Energy calibration of LHAASO-KM2A using the cosmic ray Moon shadow
No full textInternational audienceWe present a precise measurement of the westward, rigidity-dependent shift of the Moon's shadow using three and a half years of cosmic-ray data collected by the Kilometer Square Array (KM2A) of the Large High Altitude Air Shower Observatory (LHAASO). These measurements enable us to calibrate the detector energy response in the range 20-260 TeV, with results showing excellent agreement with the response derived from Monte Carlo (MC) simulations of the KM2A detector. We also measure a best-fit parameter , corresponding to a 95% confidence interval of [-14%, +17%] for the energy-scale estimation. This result establishes the exceptional accuracy of the KM2A-MC in simulating the detector's response within this energy range
Euclid Quick Data Release (Q1). Exploring galaxy morphology across cosmic time through Sersic fits
No full textInternational audienceWe present the results of the single-component Sérsic profile fitting for the magnitude-limited sample of \IE<23 galaxies within the 63.1 deg area of the Euclid Quick Data Release (Q1). The associated morphological catalogue includes two sets of structural parameters fitted using \texttt{SourceXtractor++}: one for VIS \IE images and one for a combination of three NISP images in \YE, \JE and \HE bands. We compare the resulting Sérsic parameters to other morphological measurements provided in the Q1 data release, and to the equivalent parameters based on higher-resolution \HST imaging. These comparisons confirm the consistency and the reliability of the fits to Q1 data. Our analysis of colour gradients shows that NISP profiles have systematically smaller effective radii () and larger Sérsic indices () than in VIS. In addition, we highlight trends in NISP-to-VIS parameter ratios with both magnitude and . From the 2D bimodality of the colour- plane, we define a that separates early- and late-type galaxies (ETGs and LTGs). We use the two subpopulations to examine the variations of across well-known scaling relations at z<1. ETGs display a steeper size--stellar mass relation than LTGs, indicating a difference in the main drivers of their mass assembly. Similarly, LTGs and ETGs occupy different parts of the stellar mass--star-formation rate plane, with ETGs at higher masses than LTGs, and further down below the Main Sequence of star-forming galaxies. This clear separation highlights the link known between the shutdown of star formation and morphological transformations in the Euclid imaging data set. In conclusion, our analysis demonstrates both the robustness of the Sérsic fits available in the Q1 morphological catalogue and the wealth of information they provide for studies of galaxy evolution with Euclid
On the impacts of halo model implementations in Sunyaev-Zeldovich cross-correlation analyses
No full textInternational audienceStatistical studies of the circumgalactic medium (CGM) using Sunyaev-Zeldovich (SZ) observations offer a promising method of studying the gas properties of galaxies and the astrophysics that govern their evolution. Forward modeling profiles from theory and simulations allows them to be refined directly off of data, but there are currently significant differences between the thermal SZ (tSZ) observations of the CGM and the predicted tSZ signal. While these discrepancies could be real, they could also be the result of decisions in the forward modeling used to build statistical measures from theory. In order to see effects of this, we compare an analysis utilizing halo occupancy distributions (HODs) implemented in halo models to simulate the galaxy distribution against previous studies, which weighted their results to match the CMASS galaxy sample, which contains nearly one million galaxies, mainly centrals of group-sized halos, selected for relatively uniform stellar mass across redshifts between 0.4 < z < 0.7. We review some of the implementation differences that can account for changes, such as miscentering, one-halo/two-halo cutoff radii, and mass ranges, all of which will need to be given the proper attention in future high-signal-to-noise studies. We find that our more thorough model predicts a signal with a 33% improved fit than the one from previous studies on the exact same sample. Additionally, we find that modifications that change the satellite fraction even by just a few percent, such as editing the halo mass range and certain HOD parameters, result in strong changes in the final signal. Although significant, this discrepancy from the modeling choices is not large enough to completely account for the existing disagreements between simulations and measurements