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The Close AGN Reference Survey (CARS). Long-term spectral variability study of the changing look AGN Mrk 1018
No full textInternational audienceChanging-look AGNs (CLAGN) are accreting supermassive black hole systems that undergo variations in optical spectral type, driven by major changes in accretion rate. Mrk 1018 has undergone two transitions, a brightening event in the 1980s and a transition back to a faint state over the course of 2-3 years in the early 2010s. We characterize the evolving physical properties of the source's inner accretion flow, particularly during the bright-to-faint transition, as well as the morphological properties of its parsec-scale circumnuclear gas. We model archival X-ray spectra from XMM-Newton, Chandra, Suzaku, and Swift, using physically-motivated models to characterize X-ray spectral variations and track Fe Kalpha line flux. We also quantify Mrk 1018's long-term multi-wavelength spectral variability from optical/UV to the X-rays. Over the duration of the bright-to-faint transition, the UV and hard X-ray flux fell by differing factors, roughly 24 and 8, respectively. The soft X-ray excess faded, and was not detected by 2021. In the faint state, when the Eddington ratio drops to log Lbol/LEdd < -1.7, the hot X-ray corona photon index shows a 'softer-when-fainter' trend, similar to that seen in some black hole X-ray binaries and samples of low-luminosity AGNs. Finally, the Fe Kalpha line flux has dropped by only half the factor of the drop in the X-ray continuum. The transition from the bright state to the faint state is consistent with the inner accretion flow transitioning from a geometrically-thin disk to an ADAF-dominated state, with the warm corona disintegrating or becoming energetically negligible, while the X-ray-emitting hot flow becoming energetically dominant. Meanwhile, narrow Fe Kalpha emission has not yet fully responded to the drop in its driving continuum, likely because its emitter extends up to roughly 10 pc
Weak lensing mass-richness relation of redMaPPer clusters in LSST DESC DC2 simulations
No full textInternational audienceContext. Cluster scaling relations are key ingredients in cluster abundance-based cosmological studies. In optical cluster cosmology, where clusters are detected through their richness, cluster-weak gravitational lensing has proven to be a powerful tool to constrain the cluster mass-richness relation. This work is conducted as part of the Dark Energy Science Collaboration (DESC), which aims to analyze the Legacy Survey of Space and Time (LSST) of the Vera C. Rubin Observatory, starting in 2026.Aims. Cluster properties inferred from weak lensing, such as mass, suffer from several sources of bias. In this paper, we aim to test the impact of modeling choices and observational systematics in cluster lensing on the inference of the mass-richness relation.Methods. We constrained the mass-richness relation of 3600 clusters detected by the redMaPPer algorithm in the cosmoDC2 extragalactic mock catalog of the LSST DESC DC2 simulation, covering 440 deg2, using number count measurements and either stacked weak lensing profiles or mean cluster masses in several intervals of richness (20 ≤ λ ≤ 200) and redshift (0.2 ≤ z ≤ 1).Results. We provide the first constraints on the redMaPPer cluster mass-richness relation detected in cosmoDC2. We find that for an LSST-like source galaxy density, our constraints are robust to changes in the concentration-mass relation, as well as the dark matter density profile modeling choices, when source redshifts and shapes are perfectly known. We find that photometric redshift uncertainties can introduce bias at the 1σ level, which could be mitigated by an overall correction factor fitted jointly with the scaling parameters. We find that including positive shear-richness covariance in the fit shifts the results by up to 0.5σ. Our constraints also offer a fair comparison to a fiducial mass-richness relation, obtained from matching cosmoDC2 halo masses to redMaPPer-detected cluster richness results
BepiColombo cruise science: overview of the mission contribution to heliophysics
No full textInternational audienceBepiColombo, the joint ESA/JAXA mission to Mercury, was launched in October 2018 and is scheduled to arrive at Mercury in November 2026 after an 8-year cruise. Like other planetary missions, its scientific objectives focus mostly on the nominal, orbiting phase of the mission. However, due to the long duration of the cruise phase covering distances between 1.2 and 0.3 AU, the BepiColombo mission has been able to outstandingly contribute to characterise the solar wind and transient events encountered by the spacecraft, as well as planetary environments during the flybys of Earth, Venus, and Mercury, and contribute to the characterisation of the space radiation environment in the inner Solar System and its evolution with solar activity. In this paper, we provide an overview of the cruise observations of BepiColombo, highlighting the most relevant science cases, with the aim of demonstrating the importance of planetary missions to perform cruise observations, to contribute to a broader understanding of Space Weather in the Solar System, and in turn, increase the scientific return of the mission
Late gas released in the young Kuiper belt could have significantly contributed to the carbon enrichment of the atmospheres of Neptune and Uranus
No full textInternational audienceContext. Exo-Kuiper belts have been observed for decades, but the recent detection of gas in some of them may change our view of the Solar System’s youth. Late gas produced by the sublimation of CO (or CO2) ices after the dissipation of the primordial gas could be the norm in young planetesimal belts. Hence, a gas-rich Kuiper belt could have been present in the Solar System. The high C/H ratios observed on Uranus and Neptune could be a clue to the existence of such late gas that could have been accreted onto young icy giants.Aims. The aim of this paper is to estimate the carbon enrichment of the atmospheres of Uranus and Neptune caused by the accretion of the gas released from a putative gas-rich Kuiper belt. We want to test whether a young, massive Kuiper belt such as that usually assumed by state-of-the-art models can explain the current C/H values of ~50–80 times the protosolar abundance for Uranus and Neptune.Methods. We developed a model that can follow the gas released in the Kuiper belt, as well as its viscous evolution and its capture onto planets. We calculated the final C/H ratio and compared it to observations. We studied the influence of several important parameters such as the initial mass of the belt, the viscosity of the disc, and the accretion efficiency.Results. We find that the assumption of a primordial Kuiper belt with a mass of tens of Earth masses leads to significant CO gas accretion onto the giants, which can lead to high C/H ratios, especially for Uranus and Neptune. We find that an initial Kuiper belt of ~50 M⊕ could entirely account for the present-day C/H enrichment in the atmospheres of Uranus and Neptune. However, given the fact that S/H is also significantly enriched in the deep atmospheres of these planets, but still less enriched than C/H, a more likely scenario is that these planets first accreted an envelope enriched in C/H and S/H in similar amounts, and that the sublimation of CO from the Kuiper belt led to an additional enrichment in C/H of perhaps 30 times the protosolar value in Neptune, and 20 times in Uranus. For the same model, the additional enrichments in C/H are 2 and 0.2 in Saturn and Jupiter, respectively.Conclusions. Our model shows that a relatively massive gas-rich Kuiper belt could have existed in the Solar System’s youth, which significantly enriched the atmospheres of Uranus and Neptune with carbon. Late gas accretion and its effect on the metallicities of the outer giant planets could be a universal scenario that also occurs in extrasolar systems. Observations of sub-Jupiter exoplanets could provide very useful information to better constrain this scenario, with an enrichment in carbon and oxygen (for sufficiently war planets) compared to other elements that should be inversely proportional to their envelope mass
The physical properties of candidate neutrino-emitter blazars
No full textInternational audienceThe processes governing the production of astrophysical high-energy neutrinos are still debated, and the sources originating them remain an open question. Among the putative emitters, active galactic nuclei have gained increasing attention. Blazars, in particular, stand out due to their ability to accelerate particles in environments with external radiation fields. Recent observations suggest they may contribute to the neutrino flux detected by IceCube. We study the physical properties of a subsample of 52 blazars proposed as candidate neutrino emitters, based on a positional cross-correlation analysis between IceCube hotspots and the 5BZCat catalog. We aim to provide a first characterization of their central engines and physical nature, to explore the potential link with neutrino production. We analyze the optical spectroscopic properties of the 52 candidate neutrino-emitter blazars to infer their accretion regime. The study is complemented by radio and -ray data, which trace the intrinsic jet power. We compare the sample to other blazar populations in the literature, perform statistical tests, and explore, through simulations, the applicability of methods that include censored data. Overall, the target sample shows properties compatible with the reference samples. We observe a mild tendency to prefer objects with intense radiation fields, typical of radiatively efficient accretors, and high radio power. Among them, 24 are detected by Fermi-LAT, spanning various -ray luminosities. We also show that statistical tests commonly used in the literature need to be handled with caution, as they are sensitive to the number of censored data and the sample size
A Radio-quiet AGN as a candidate counterpart to neutrino event IceCube-200615A
No full textInternational audienceFollow-up observations of neutrino events have been a promising method for identifying sources of very-high-energy cosmic rays. Neutrinos are unambiguous tracers of hadronic interactions and cosmic rays. On June 15, 2020, IceCube detected a neutrino event with an 82.8% probability of being astrophysical in origin. To identify the astrophysical source of the neutrino, we used X-ray tiling observations to identify potential counterpart sources. We performed additional multiwavelength follow-up with NuSTAR and the VLA in order to construct a broadband spectral energy distribution (SED) of the most likely counterpart. From the SED, we calculate an estimate for the neutrinos we expect to detect from the source. While the source does not have a high predicted neutrino flux, it is still a plausible neutrino emitter. It is important to note that the other bright X-ray candidate sources consistent with the neutrino event are also radio-quiet AGN. A statistical analysis shows that 1RXS J093117.6+033146 is the most likely counterpart (87.5%) if the neutrino is cosmic in origin and if it is among X-ray detectable sources. This results adds to previous results suggesting a connection between radio-quiet AGN and IceCube neutrino events
Infalling Ultra Faint Dwarfs as Emissaries of the Axiverse?
No full textInternational audienceRecent discoveries of Ultra Faint dwarf galaxies (UFG's) infalling onto the Milky Way, namely Leo K & M at kpc, considerably strengthens the case that UFG's constitute a distinct galaxy class that is inherently smaller, fainter and metal poor compared to the classical dwarf spheroidals (dSph). This distinction is at odds with the inherent continuity of galaxy halo masses formed under scale-free gravity for any standard dark matter model. Here we show that distinct galaxy classes do evolve in cosmological simulations of multiple light bosons representing the 'Axiverse' proposal of String Theory, where a discrete mass spectrum of axions is generically predicted to span many decades in mass. In this context, the observed UFG class we show corresponds to a relatively heavy boson of eV, including Leo K & M, whereas a lighter axion of eV comprises the bulk of dark matter in all larger galaxies including the dSph's. Although Leo M is larger in size than Leo K, we predict its velocity dispersion to be smaller km/s, compared to km/s for Leo K, since soliton cores are required by the Uncertainty Principle to be wider at lower momentum. This scenario can be definitively tested using millisecond pulsars close to the Galactic center, where the Compton frequencies of the heavy and light bosons imprint monotone timing residuals that may be detected by SKA on timescales of approximately 1 week and 4 months, respectively
Search for single production of vector-like quarks decaying into in collisions at TeV with the ATLAS detector
No full textInternational audienceA search for single production of a vector-like quark , which could be either a singlet , with charge , or a from a triplet, with charge , is performed using data from proton-proton collisions at a centre-of-mass energy of 13 TeV. The data correspond to the full integrated luminosity of 140 fb recorded with the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis targets decays where the boson decays leptonically. The data are found to be consistent with the expected Standard Model background, so upper limits are set on the cross-section times branching ratio, and on the coupling of the to the Standard Model sector for these two benchmark models. Effects of interference with the Standard Model background are taken into account. For the singlet , the 95% confidence level limit on the coupling strength ranges between 0.22 and 0.52 for masses from 1150 to 2300 GeV. For the triplet, the limits on vary from 0.14 to 0.46 for masses from 1150 to 2600 GeV
Building confidence in models for complex barrier systems for radionuclides
No full textInternational audienceThe modeling and simulation of the Cement–clay Interaction–Diffusion field (CI-D) experiment at the Mont Terri site in Switzerland presented here demonstrates that it is possible to capture the multiscale physical and chemical features of natural and engineered barrier systems for radionuclides. The simulations are successfully carried out with the newly developed CrunchODiTi high-performance computing software that accounts for multiple continua, including a continuum representing the electrical double layer (EDL) developed along negatively charged clay particles in clay rock. The simulation also accounts for both the complex three-dimensional (3D) geometry, expected as the norm in a geological waste repository, and the anisotropy of the geological formation. In addition, the high resolution of the model makes it possible to include “skin effects” developed at the interface between highly reactive materials, in this case between the high pH cement and the circumneutral but electrostatic Opalinus Clay. The successful history matching with the field experiment demonstrates that the distinct geochemical and physical properties of the cement and the Opalinus Clay in the CI-D experiment can be accounted for. Such analyses are essential for developing a defensible safety case for the underground storage of radioactive waste
Evidence for a sub-Jovian planet in the young TWA 7 disk
No full textInternational audiencePlanets are thought to form from dust and gas in protoplanetary disks, with debris disks being the remnants of planet formation. Aged a few million up to a few billion years, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies1,2. Tens of debris disks, with sizes of tens, sometimes hundreds, of astronomical units have been resolved with high-spatial-resolution, high-contrast imagers at optical and near-infrared or (sub)millimetre interferometers3,4. They commonly show cavities, ring-like structures and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals2,5. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2–10 MJ) of high-contrast imaging instruments (see, for example, refs. 6,7,8,9) before the James Webb Space Telescope. Here we have used the unprecedented sensitivity of the James Webb Space Telescope’s Mid-Infrared Instrument10,11 in the thermal infrared to search for such planets in the disk of the approximately 6.4-Myr-old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arcsec from the star, which is best interpreted as a cold, sub-Jupiter-mass planet. Its estimated mass (about 0.3 MJ) and position (about 52 au, de-projected) can thoroughly account for the main disk structures