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GWTC-4.0: Searches for Gravitational-Wave Lensing Signatures
No full textInternational audienceGravitational waves can be gravitationally lensed by massive objects along their path. Depending on the lens mass and the lens--source geometry, this can lead to the observation of a single distorted signal or multiple repeated events with the same frequency evolution. We present the results for gravitational-wave lensing searches on the data from the first part of the fourth LIGO--Virgo--KAGRA observing run (O4a). We search for strongly lensed events in the newly acquired data by (1) searching for an overall phase shift present in an image formed at a saddle point of the lens potential, (2) looking for pairs of detected candidates with consistent frequency evolution, and (3) identifying sub-threshold counterpart candidates to the detected signals. Beyond strong lensing, we also look for lensing-induced distortions in all detected signals using an isolated point-mass model. We do not find evidence for strongly lensed gravitational-wave signals and use this result to constrain the rate of detectable strongly lensed events and the merger rate density of binary black holes at high redshift. In the search for single distorted lensed signals, we find one outlier: GW231123_135430, for which we report more detailed investigations. While this event is interesting, the associated waveform uncertainties make its interpretation complicated, and future observations of the populations of binary black holes and of gravitational lenses will help determine the probability that this event could be lensed
The odyssey of the black hole low mass X-ray binary GX339-4: Five years of dense multi-wavelength monitoring
No full textInternational audienceWe present the longest and the densest quasi-simultaneous radio, X-ray and optical campaign of the black hole low mass X-ray binary GX339-4, covering five years of weekly GX339-4 monitoring with MeerKAT, Swift-XRT and MeerLICHT, respectively. Complementary high frequency radio data with the Australia Telescope Compact Array are presented to track in more detail the evolution of GX339-4 and its transient ejecta. During the five years, GX339-4 has been through two "hard-only" outbursts and two "full" outbursts, allowing us to densely sample the rise, quenching and re-activation of the compact jets. Strong radio flares were also observed close to the transition between the hard and the soft states. Following the radio flare, a transient optically thin ejection was spatially resolved during the 2020 outburst, and was observed for a month. We also discuss the radio/X-ray correlation of GX339-4 during this five year period, which covers several states in detail from the rising phase to the quiescent state. This campaign allowed us to follow ejection events and provide information on the jet proper motion and its intrinsic velocity. With this work we publicly release the weekly MeerKAT L-band radio maps from data taken between September 2018 and October 2023
Energetic particles accelerated via turbulent magnetic reconnection in protoplanetary discs - I. Ionisation rates
No full textInternational audienceContext. Ionisation controls the chemistry, thermal balance, and magnetic coupling in protoplanetary discs. However, standard ionisation vectors such as stellar UV, X-rays, Galactic cosmic rays (GCRs) might not be efficient enough, as UV/X-rays are attenuated rapidly with depth, while GCRs are modulated. Turbulence-induced magnetic reconnection in disc atmospheric layers offers a physically motivated, in situ source of energetic particles (EPs) that has never been considered. Aims. We quantify the ionisation and heating produced by EPs accelerated by turbulent reconnection, identify where they dominate over X-rays and GCRs, and determine energetic thresholds for their relevance. We provide scalable diagnostics tied to the local energy budget. Methods. We adopt a Fermi-like acceleration model with parameters linked to a turbulent reconnection geometry trigger by the magneto-rotational instability, yielding a steady-state energy distribution of the EP forming a power-law of index . We propagate electrons and protons through the disc and compute primary and secondary ionisation and associated heating on a fiducial T Tauri disc model background. The non-thermal normalisation is set by the fraction of local viscous accretion energy dissipation channelled to EPs, parametrised by . Results. For , EPs ionisation overpass standard ionisation sources in the disc atmosphere and intermediate/deep layers out to radii of a few tens of astronomical units. Even at , EPs contribute at the few-percent level, thus are chemically and dynamically relevant. These results identify EPs accelerated by turbulence-induced magnetic reconnection as a rather robust, disc-internal ionisation channel that should be included in thermo-chemical models of protoplanetary discs
Impact of active galactic nuclei and nuclear star formation on the ISM turbulence of galaxies: Insights from JWST/MIRI spectroscopy
No full textInternational audienceActive galactic nuclei (AGNs), star formation (SF), and galaxy interactions can drive turbulence in the gas of the interstellar medium (ISM), which, in turn, plays a role in SF taking place within galaxies. The impact on molecular gas is of particular importance, as it serves as the primary fuel for SF. Our goal is to investigate the origin of turbulence and the emission of molecular gas, as well as low-and-intermediate-ionisation gas, in the inner few kpc of both AGN hosts and star-forming galaxies (SFGs). We used archival JWST MIRI/MRS observations of a sample consisting of 54 galaxies at z < 0.1. We present flux measurements for the H2 S(5)λ6.9091 μm, [ArII]λ6.9853 μm, [FeII]λ5.3403 μm, and [ArIII]λ8.9914 μm emission lines along with velocity dispersion estimated by the W80 parameter. For galaxies with coronal line emission, we included measurements of the [MgV]λ5.6098 μm line. We compared the line ratios to photoionisation and shock models to explore the origin of the gas emission. AGNs exhibit broader emission lines than SFGs, with the largest velocity dispersions observed in radio-strong (RS) AGNs. The H2 gas is less turbulent compared to ionised gas, while coronal gas presents higher velocity dispersions. The W80 values for the ionised gas show a decrease when going from the nucleus out to radii of approximately 0.5–1 kpc, followed by an outward increase up to 2–3 kpc. In contrast, the H2 line widths generally display increasing profiles with distance from the center. Correlations between the W80 parameter and line ratios such as H2S(5)/[Ar II] and [Fe II]/[Ar II] indicate that the most turbulent gas is associated with shocks, enhancing H2 and [Fe II] emissions. Based on the observed line ratios and velocity dispersions, the [FeII] emission is consistent with predictions of fast shock models, while the H2 emission is likely associated with molecules formed in the post-shock region. We speculate that these shocked gas regions are produced by AGN outflows and jet-cloud interactions in AGN-dominated sources; whereas in SFGs, they might be created through stellar winds and mergers. This shock-induced gas heating may be an important mechanism of AGN (or stellar) feedback, preventing the gas from cooling and forming new stars.Key words: galaxies: active / galaxies: evolution / galaxies: ISM / galaxies: kinematics and dynamic
Effect of noise characterization on the detection of mHz stochastic gravitational waves
No full textInternational audiencePulsar timing arrays' hint for a stochastic gravitational-wave background (SGWB) leverages the expectations of a future detection in the millihertz band, particularly with the LISA space mission. However, finding an SGWB with a single orbiting detector is challenging: It calls for cautious modelling of instrumental noise, which is also mainly stochastic. It was shown that agnostic noise reconstruction methods provide robustness in the detection process. We build on previous work to include more realistic instrumental simulations and additional degrees of freedom in the noise inference model and analyze the impact of LISA's sensitivity to SGWBs. Particularly, we model the two main types of noise sources with separate transfer functions and power spectral density spline fitting. We assess the detectability bounds and their dependence on the flexibility of the noise model and on the prior probability, allowing us to refine previously reported results
Euclid: Early Release Observations -- The extended stellar component of the IC10 dwarf galaxy
No full textInternational audienceWe present a detailed analysis of the old, extended stellar component of the Local Group dwarf galaxy IC 10 using deep resolved-star photometry in the VIS and NISP bands of the Euclid Early Release Observations. Leveraging Euclid's unique combination of wide field of view and high spatial resolution, we trace red giant branch (RGB) stars out to 8 kpc from the galaxy centre, reaching azimuthally-averaged surface brightness levels as faint as 29 mag arcsec. Our analysis reveals that IC 10's stellar distribution is significantly more extended than previously thought. After correcting for foreground extinction and subtracting contamination from Milky Way stars and background galaxies, we derive a radial stellar density profile from RGB star counts. The profile shows a marked flattening beyond 5 kpc, and is best fit by a two-component (Sersic + exponential) model, yielding a total stellar mass in old (age 1 Gyr) stars of . The origin of the outer stellar component is unclear. It may be accreted, even possibly associated with the counter-rotating HI gas in the outer regions of IC 10, or it may represent an ancient in-situ stellar halo. We tentatively detect two symmetric stellar overdensities at the edge of our imagery. These roughly align with the direction of IC 10's orbit around M31, suggesting that they may be signatures of tidal stripping. As part of our analysis, we derive a new distance to IC 10 based on the RGB tip, finding kpc and the distance modulus is
Euclid preparation. 3D reconstruction of the cosmic web with simulated Euclid Deep spectroscopic samples
No full textInternational audienceThe ongoing Euclid mission aims to measure spectroscopic redshifts for approximately two million galaxies using the H line emission detected in near-infrared slitless spectroscopic data from the Euclid Deep Fields (EDFs). These measurements will reach a flux limit of in the redshift range , opening the door to numerous investigations involving galaxy evolution, extending well beyond the mission's core objectives. The achieved H luminosity depth will lead to a sufficiently high sampling, enabling the reconstruction of the large-scale galaxy environment. We assess the quality of the reconstruction of the galaxy cosmic web environment with the expected spectroscopic dataset in EDFs. The analysis is carried out on the Flagship and GAEA galaxy mock catalogues. The quality of the reconstruction is first evaluated using geometrical and topological statistics measured on the cosmic web, namely the length of filaments, the area of walls, the volume of voids, and its connectivity and multiplicity. We then quantify how accurately gradients in galaxy properties with distance from filaments can be recovered. As expected, the small-scale redshift-space distortions, have a strong impact on filament lengths and connectivity, but can be mitigated by compressing galaxy groups before skeleton extraction. The cosmic web reconstruction is biased when relying solely on H emitters. This limitation can be mitigated by applying stellar mass weighting during the reconstruction. However, this approach introduces non-trivial biases that need to be accounted for when comparing to theoretical predictions. Redshift uncertainties pose the greatest challenge in recovering the expected dependence of galaxy properties, though the well-established stellar mass transverse gradients towards filaments can still be observed
What can be learnt from UHECR anisotropies observations Paper III: Update with new data and Galactic magnetic fields models
No full textInternational audienceContext. At large angular scales, the Pierre Auger Observatory has reported a significant dipole modulation in right ascension, while at intermediate angular scales, localized flux excesses have been identified by both the Auger and Telescope Array collaborations. These observations were investigated in the first two papers of this series. Aims. We examine the implications of these anisotropy measurements and assess to what extent they can be used to constrain the origin of UHECRs and the astrophysical or physical parameters of viable source scenarios. Methods. As in the first two papers of this series, we generate realistic UHECR sky maps for a wide range of astrophysical models consistent with current spectral and composition constraints, assuming that UHECR sources trace the distribution of galaxies in the Universe. We update our previous studies by incorporating the most recent models of the Galactic magnetic field and apply the same large- and intermediate-scale anisotropy analyses as those used by the Auger Collaboration to simulated datasets with current experimental exposure. Results. The main novelty of this third paper is the improved compatibility between simulations and data, in particular regarding the reconstructed dipole direction, when using several of the recently proposed Galactic magnetic field models. Despite this progress, our main conclusions remain unchanged: although the observed anisotropies are compatible with an extragalactic origin of UHECRs, present data and magnetic-field uncertainties do not allow strong constraints to be placed on the nature, spatial distribution, or density of UHECR sources. Conclusions. Further progress in the interpretation of UHECR anisotropies will require improved constraints on cosmic magnetic fields, advances in source modeling, and significantly larger experimental exposure
Looking for observational signatures of early binary black hole systems
No full textInternational audienceContext. A lot of recent studies have focused on the observables associated with near merger binary black-holes (BBHs) embedded in a circumbinary disk (CBD) but we still we lack knowledge of observables of BBHs in their early stage. In that stage the separation between the two black holes is so large that both black holes could potentially retain their individual accretion disk existing before the creation of the BBH. For such early BBH systems, it is interesting to look for observables originating in those individual disks whose structure is likely to differ from mini-disks often observed in simulations of later stages of BBHs. Aims. In a companion paper we presented a set of hydrodynamical simulations of an individual disk surrounding a primary black hole while being impacted by the presence of a secondary black-hole in an early BBH system, leading to the creation of three well-known characteristic features in the disk's structure. Here we explore the imprints of these three features on the observables associated with the thermal emission of the pre-existing black hole disk. The aim is two-fold, first to see which observables are best suited for detecting those early systems and, secondly, what could be extrapolated about these systems from observations. Methods. We used general relativistic ray-tracing in order to produce synthetic observations of the thermal emission emitted by early BBHs with different mass ratio and separations in order to search for distinctive observational features of early systems. Results. We found that in the case of early BBH with pre-existing disk(s) a necessary, although not unique, observational feature is the truncation of their disk(s). Conclusions. Such observable could be used for automated search of potential BBHs and discriminate some existing candidates
A HyperFlash and ECLAT view of the local environment and energetics of the repeating FRB 20240619D
No full textInternational audienceTime-variable propagation effects provide a window into the local plasma environments of repeating fast radio burst (FRB) sources. Here we report high-cadence observations of FRB 20240619D, as part of the HyperFlash and ÉCLAT programs. We observed for h and detected bursts, including bursts with high fluence ( Jy ms) and implied energy. We track burst-to-burst variations in dispersion measure (DM) and rotation measure (RM), from which we constrain the parallel magnetic field strength in the source's local environment: mG. Apparent DM variations between sub-bursts in a single bright event are interpreted as coming from plasma lensing or variable emission height. We also identify two distinct scintillation screens along the line of sight, one associated with the Milky Way and the other likely located in the FRB's host galaxy or local environment. Together, these (time-variable) propagation effects reveal that FRB 20240619D is embedded in a dense, turbulent and highly magnetised plasma. The source's environment is more dynamic than that measured for many other (repeating) FRB sources, but less extreme compared to several repeaters that are associated with a compact, persistent radio source. FRB 20240619D's cumulative burst fluence distribution shows a power-law break, with a flat tail at high energies. Along with previous studies, this emphasises a common feature in the burst energy distribution of hyperactive repeaters. Using the break in the burst fluence distribution, we estimate a source redshift of -. We discuss FRB 20240619D's nature in the context of similar studies of other repeating FRBs