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No full textLa journée PIF19 s’est déroulée le 15 novembre 2025 dans le grand amphithéâtre du site de la Bibliothèque nationale de France (BnF), qui les coorganise avec la SFP depuis l’an 2000. La rencontre a accueilli 135 personnes et 700 environ ont suivi les exposés en streaming
Prediction of rainfall noise radiated by sandwich panels using the Finite Transfer Matrix Method
No full textMultilayer elements, such as sandwich panels, are often used to form the roof of a building or car; hence validated prediction models are needed to determine the sound radiated by them during rainfall. To calculate the radiation efficiency of a sandwich panel formed from two plates and a porous material, the Finite Transfer Matrix Method (FTMM) has been used with an order-reduced integral equation and an additional term to account for nearfield radiation because, in comparison with homogeneous plates, sandwich panels tend to have high damping. Transfer mobility measurements on the sandwich panel showed that vibrational energy was concentrated near the point of excitation due to the panel being highly damped, and confirmed the validity of the limp porous material model for the foam that was used as the porous material. Experimental validation of the prediction models used artificial rain with drops impacting at approximately terminal velocity. This demonstrated that it was necessary to include the effect of nearfield radiation in the overall radiation efficiency. An assessment of existing empirical and semi-empirical models for the time-dependent force applied by liquid water drops showed that for this application of artificial rain in the laboratory it was reasonable to assume a dry surface when predicting the structure-borne sound power input
Looking for observational signatures of early binary black hole systems
No full textContext. Many recent studies have focused on the observables associated with near-merger binary black-holes (BBHs) embedded in a circumbinary disk, but we still lack knowledge of the observables of BBHs in their early stage. In this stage, the separation between the two black holes is so large that both black holes could potentially retain the individual accretion disks that existed before the BBH was created. For such early BBH systems, it is interesting to look for observables originating in these individual disks, as their structure is likely to differ from that of mini-disks that are often observed in simulations of later BBH stages.
Aims. In a companion paper, we presented a set of hydrodynamical simulations of an individual disk surrounding a primary black hole while it was affected by a secondary black hole in an early BBH system. This created three well-known characteristic features in the disk structure. Here, we explore the imprints of these three features on the observables associated with the thermal emission of the preexisting black hole disk. Our aim was twofold: we first determined which observables were best suited for detecting these early systems, and second, we determined what we might extrapolate about these systems based on 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 BBHs with preexisting disk(s), a necessary, although not unique, observational feature is the truncation of their disk(s).
Conclusions. This observable might be used for an automated search of potential BBHs and to potentially rule out some existing candidates
HR6819: a puffed-up stripped star system challenging stable mass transfer theory
No full textContext. HR6819 is the first system with a puffed-up low-mass stripped star + a classical Be star whose nature has been confirmed by optical interferometry. The system exhibits the most extreme mass ratio (15.7 ± 1.1), the lowest stripped star mass (0.270 ± 0.056 M⊙), and one of the shortest orbital periods (40.3266 ± 0.0016 days) compared to similar observed binaries. As a post mass transfer candidate, HR6819 offers a unique opportunity to test the physics of binary interaction, especially the fraction of mass accreted by the Be progenitor (the efficiency of the mass transfer) required to produce the system’s extreme mass ratio.
Aims. This work aims to reconstruct the possible evolutionary history of HR6819 in the context of stable mass transfer via Roche lobe overflow. We want to explore how the tight constraints on the system’s total mass, mass ratio and orbital period are limiting the range of possible progenitors of the system.
Methods. Based on analytical expectations for the orbital evolution, we build grids of MESA simulations designed to match the present-day orbital period and mass ratio of the system, with different mass transfer efficiencies from fully conservative to 50% efficient.
Results. We show that evolution via stable mass transfer cannot explain the combined extreme current mass ratio and tight orbital period of the system. There is a limit on how extreme the post-mass transfer mass ratio of the progenitor binary can be at a fixed detachment period, and this limit is dependent on the efficiency of the mass transfer episode: the less efficient the mass transfer episode, the less extreme the mass ratio at detachment. Even in the case of fully conservative mass transfer, the most extreme mass ratio we can produce with binary evolution simulations is q ∼ 11.5 at P ∼ 40 days, which is significantly below the observed value. We also show that the reported luminosities for each component significantly exceed the value expected from their mass. In particular, based on simple stripped star models, we find that the luminosity of the bloated stripped star requires a star with a mass of ∼0.7 M⊙, which is over twice the measured value.
Conclusions. Our work shows that the post-interaction properties of HR6819, especially its extreme mass ratio and orbital period, cannot be produced by stable mass transfer under standard assumptions
CTAO LST–1 observations of magnetar SGR 1935+2154: Deep limits on sub-second bursts and persistent tera-electronvolt emission
No full textContext. The Galactic magnetar SGR 1935+2154 has exhibited prolific high-energy (HE) bursting activity in recent years.
Aims. Investigating its potential tera-electronvolt counterpart could provide insights into the underlying mechanisms of magnetar emission and very high-energy (VHE) processes in extreme astrophysical environments. We aim to search for a possible tera-electronvolt counterpart to both its persistent and sub-second-scale burst emission.
Methods. We analysed over 25 hour of observations from the Large-Sized Telescope prototype (LST−1) of the Cherenkov Telescope Array Observatory (CTAO) during periods of HE activity from SGR 1935+2154 in 2021 and 2022 to search for persistent emission. For bursting emission, we selected and analysed nine 0.1 s time windows centred around known short X-ray bursts, targeting potential sub-second-scale tera-electronvolt counterparts in a low-photon-statistics regime.
Results. While no persistent or bursting emission was detected in our search, we establish upper limits for the tera-electronvolt emission of a short magnetar burst simultaneous to its soft gamma-ray flux. Specifically, for the brightest burst in our sample, the ratio between tera-electronvolt and X-ray flux is ≲10−3.
Conclusions. The non-detection of either persistent or bursting tera-electronvolt emission from SGR 1935+2154 suggests that if such components exist, they may occur under specific conditions not covered by our observations. This aligns with theoretical predictions of VHE components in magnetar-powered fast radio bursts and the detection of MeV–GeV emission in giant magnetar flares. These findings underscore the potential of magnetars, fast radio bursts, and other fast transients as promising candidates for future observations in the low-photon-statistics regime with Imaging Atmospheric Cherenkov Telescopes, particularly with the CTAO
The relationship between the emission line, continuum luminosity, and Baldwin effect in blazars
No full textAims. This study investigates the relationship between the Mg II λ2798 Å emission line and the 3000 Å continuum luminosity, as well as the Baldwin effect, in a sample of 40’,685 radio-quiet (RQ) quasars and 441 flat spectrum radio quasars (FSRQs).
Methods. We performed a comprehensive re-evaluation of the Mg II-3000 Å correlation, explicitly accounting for dispersion introduced by active galactic nucleus (AGN) variability. After excluding > 3000 radio-loud sources, we employed a binning technique to mitigate variability effects, yielding a refined empirical relation. We also further examined the nonthermal dominance (NTD) parameter, to investigate the dominant source of the continuum.
Results. Our analysis reveals statistically significant differences in the slopes of the line-continuum luminosity relation between RQ quasars and FSRQs, with a parallel discrepancy in the Baldwin effect. These findings imply either (1) intrinsic differences in the accretion disk spectra of RQ AGNs and FSRQs or (2) jet-induced continuum emission in FSRQs contributing to broad line region (BLR) ionization. We also find that a substantial fraction of both RQ quasars (43.8%) and blazars (55.5%) exhibit NTD < 1. For blazars, this suggests that the accretion disk alone cannot fully explain BLR ionization. On the other hand, we interpret NTD < 1 in radio-quiet quasars as a signature of several physical mechanisms: anomalies in the BLR structure (such as outflow or inflows), time lags between continuum and line variations, and the suppression of the UV continuum by a strong corona that diverts accretion power. Finally, we demonstrate that the Baldwin effect naturally emerges from the line-continuum luminosity relationship, requiring no additional physical mechanism to explain its origin