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The Radio Flare and Multiwavelength Afterglow of the Short GRB 231117A: Energy Injection from a Violent Shell Collision
No full textInternational audienceWe present the early radio detection and multiwavelength modeling of the short gamma-ray burst (GRB) 231117A at redshift z = 0.257. The Australia Telescope Compact Array automatically triggered a 9 hr observation of GRB 231117A at 5.5 and 9 GHz following its detection by the Neil Gehrels Swift Observatory just 1.3 hr post-burst. Splitting this observation into 1 hr time bins, the early radio afterglow exhibited flaring, scintillating and plateau phases. The scintillation allowed us to place the earliest upper limit (<10 hr) on the size of a GRB blast wave to date, constraining it to <1 × 10 16 cm. Multiwavelength modeling of the full afterglow required a period of significant energy injection between ∼0.02 and 1 day. The energy injection was modeled as a violent collision of two shells: a reverse shock passing through the injection shell explains the early radio plateau, while an X-ray flare is consistent with a shock passing through the leading impulsive shell. Beyond 1 day, the blast wave evolves as a classic decelerating forward shock with an electron distribution index of p = 1.66 ± 0.01. Our model also indicates a jet break at ∼2 days, and a half-opening angle of = °± °16.61 .1 j . Following the period of injection, the total energy is ζ ∼ 18 times the initial impulsive energy, with a final collimation-corrected energy of E Kf ∼ 5.7 × 10 49 erg. The minimum Lorentz factors this model requires are consistent with constraints from the early radio measurements of Γ > 35 to Γ > 5 between ∼0.1 and 1 day. These results demonstrate the importance of rapid and sensitive radio follow-up of GRBs for exploring their central engines and outflow behaviour.</p
2D hybrid simulations of Hall Thrusters: effect of self-consistently generated multiply charged ions
No full textInternational audienceHall Thrusters (HTs) enable in-space mobility using E × B plasma discharge principles. Presence of multiply charged ions in these devices has been repeatedly observed, and reported to affect thruster operation. In this study, we examine the impact of doubly charged ions using a two-dimensional hybrid particle-in-cell/Monte Carlo collision (PIC/MCC) simulation of the SPT-100 thruster. The simulation operates at an anode voltage of 500 V and a xenon mass flow rate of 5 mg/s. Double ionization of neutral xenon and single ionization of Xe+ are incorporated as mechanisms for self-consistent Xe2+ generation.Both processes are found to be of comparable significance. Breathing mode oscillations are captured by the model and shown to modulate differently the two Xe2+ production pathways. Results show that Xe2+ ions contribute approximately to 17 % of the total discharge current, and that their presence leads to higher discharge current, thrust, and specific impulse
Investigations of the Moon Phobos by Mars Express and Implications Towards Its Origin
No full textInternational audienceMars Express has opened a new chapter in the exploration of Phobos, thanks to its elliptical orbit that allows for regular flybys, sometimes as close as 50 km. Initially designed for studying Mars' surface and atmosphere, its instruments have provided a wealth of data, including precise geophysical bulk parameters, insights into Phobos' interior, high-resolution images, remote sensing data of its surface, and observations of interactions between Phobos and the space environment. This resurgence of interest in the Martian moons revolves around the fundamental question of how they formed. Despite the abundance of data gathered by Mars Express, Phobos' surface composition remains uncertain with many unresolved questions. This ambiguity prevents a definitive confirmation or refutation of the asteroid capture scenario, which likens Phobos to a D-type asteroid. This scenario contradicts the current orbits of the moons and poses other dynamical challenges. However, an alternative hypothesis suggests that Phobos and Deimos formed through the accretion of a rocky debris disk in Mars' orbit. Their refined shapes, low mass, and bulk density support this idea. The non-detection of MARSIS echoes implies a porous interior, aligning with the low bulk density, indicative of high porosity. The next phase of Phobos exploration will be led by JAXA's Mars Moon eXplorer (MMX) mission, set to quasi-orbit Phobos, land on its surface, and return a sample to Earth in 2029
Caractérisation des erreurs systématiques dues aux inhomogénéités d'intensité des faisceaux Raman dans un gravimètre absolu à atomes froids
No full textCorrelations between the internal and external degrees of freedom of neutral atoms enable state-of-the-art accuracy and sensitivity in inertial sensors. This thesis presents the latest developments in the absolute cold-atom gravimeter (CAG) of the LTE, based on momentum-state interferometry using Raman transitions in a freely falling atomic cloud of 87 Rb. We identify intensity inhomogeneities as a primary source of contrast loss in the CAG and highlight the role of non-resonant interactions resulting from the counter propagating geometry of the Raman beams. Following optimization of the optical setup, the interferometer contrast improved by nearly 10%, with local intensity-related features successfully eliminated. Additionally, we identified bias phases arising from intensity variations, predominantly during the mirror pulse. We introduce a dynamical method for evaluating these phase shifts, which generalizes the traditional adiabatic approximation. This method enables us to distinguish between phase shifts caused by two-photon processes and those of other origins. Crucially, it links the population of stray momentum states to the accumulation of nonlinear phase shifts at the interferometers output ports. We report a systematic bias in the measurement of g at the level of 5 × 10−9 g, attributed to intensity inhomogeneities, and a sensitivity of 20 × 10−9 g Hz−1/2.Les corrélations entre les degrés de liberté internes et externes des atomes neutres permettent d'atteindre une précision et une sensibilité de pointe dans les capteurs inertiels. Cette thèse présente les derniers développements réalisés sur le gravimètre absolu à atomes froids (CAG) du LTE, basé sur l'interférométrie d’états de moment via des transitions Raman dans un nuage d'atomes de 87 Rb en chute libre. Nous identifions les inhomogénéités d'intensité comme la principale source de perte de contraste dans le CAG, et mettons en évidence le rôle des interactions non résonantes induites par la géométrie contre-propagative des faisceaux Raman. Après optimisation du dispositif optique, le contraste de l'interféromètre s'est amélioré de près de 10 %, et les structures locales liées au champ ont été éliminées. Par ailleurs, nous avons identifié des phases de biais provenant des variations d'intensité laser, principalement pendant l'impulsion miroir. Nous introduisons une méthode dynamique pour évaluer ces déphasages, qui constitue une généralisation de l'approximation adiabatique classique. Cette approche permet de distinguer les déphasages causés par des processus à deux photons de ceux ayant une autre origine. Elle relie notamment la population d'états de moment indésirables à l'accumulation de phases non linéaires aux sorties de l'interféromètre. Nous rapportons un biais systématique dans la mesure de g de l'ordre de 5 × 10−9 g, attribué aux inhomogénéités d'intensité, ainsi qu'une sensibilité de 20 × 10−9 g Hz−1/2
Peeling at extreme black hole horizons
No full text33 pages, 3 figuresInternational audienceThe starting point of this work was an intriguing similarity between the behaviour of fields near a degenerate horizon and near the infinity of an asymptotically flat spacetime, as revealed by the scattering theory for Dirac fields in the ``exterior'' region of the extreme Kerr - de Sitter black hole, developed by one of the authors (JB). However, in that situation, the comparison was somewhat clouded by some of the analytical techniques used in intermediate steps of the proof. The aim of the present work is to clarify the comparison further by studying instead the peeling behaviour of solutions to the wave equation at an extremal horizon. We focus first on the extreme Reissner-Nordstr\"om black hole, for which the Couch-Torrence inversion (a global conformal isometry that exchanges the horizon and infinity) makes the analogy explicit. Then, we explore more general spherically symmetric situations using the Couch-Torrence inversion outside of its natural context
Galaxy formation with Wave/Fuzzy Dark Matter: The core-halo structure
No full textInternational audienceDark matter-dominated cores have long been claimed for the well-studied local group dwarf galaxies. More recently, extended stellar halos have been uncovered around several of these dwarfs through deeper imaging and spectroscopy. Such core-halo structures are not a feature of conventional cold dark matter (CDM), based on collisionless particles where smooth, scale-free profiles are predicted. In contrast, smooth and prominent dark matter cores are predicted for Warm and Fuzzy/Wave Dark Matter (WDM/DM) respectively. The question arises to what extent the visible stellar profiles should reflect this dark matter core structure. Here we compare cosmological hydrodynamical simulations of CDM, WDM DM, aiming to predict the stellar profiles for these three DM scenarios. We show that cores surrounded by extended halos are distinguishable for WDM and DM, with the most prominent cores in the case of DM, where the stellar density is enhanced in the core due to the presence of the relatively dense soliton. Our analysis demonstrates that such behavior does not appear in CDM, implying that the small-scale cut-off in the power spectrum present for WDM and DM provides a core-halo transition. Consequently, we estimate the mass of the DM particle at this core-halo transition point. Furthermore, we observe the anticipated asymmetry for DM due to the soliton's random walk, a distinctive characteristic not found in the symmetric distributions of stars in Warm and CDM models
Magnetic-induced force noise in LISA Pathfinder free-falling test masses
No full textInternational audienceLISA Pathfinder was a mission designed to test key technologies required for gravitational wave detection in space. Magnetically driven forces play a key role in the instrument sensitivity in the low-frequency regime, which corresponds to the measurement band of interest for future space-borne gravitational wave observatories. Magnetic-induced forces couple to the test mass motion, introducing a contribution to the relative acceleration noise between the free falling test masses. In this Letter we present the first complete estimate of this term of the instrument performance model. Our results set the magnetic-induced acceleration noise during the February 2017 noise run of at 1 mHz and at 0.1 mHz. We also discuss how the non-stationarities of the interplanetary magnetic field can affect these values during extreme space weather conditions
Euclid preparation. Sensitivity to non-standard particle dark matter model
No full textInternational audienceThe Euclid mission of the European Space Agency will provide weak gravitational lensing and galaxy clustering surveys that can be used to constrain the standard cosmological model and its extensions, with an opportunity to test the properties of dark matter beyond the minimal cold dark matter paradigm. We present forecasts from the combination of these surveys on the parameters describing four interesting and representative non-minimal dark matter models: a mixture of cold and warm dark matter relics; unstable dark matter decaying either into massless or massive relics; and dark matter experiencing feeble interactions with relativistic relics. We model these scenarios at the level of the non-linear matter power spectrum using emulators trained on dedicated N-body simulations. We use a mock Euclid likelihood to fit mock data and infer error bars on dark matter parameters marginalised over other parameters. We find that the Euclid photometric probe (alone or in combination with CMB data from the Planck satellite) will be sensitive to the effect of each of the four dark matter models considered here. The improvement will be particularly spectacular for decaying and interacting dark matter models. With Euclid, the bounds on some dark matter parameters can improve by up to two orders of magnitude compared to current limits. We discuss the dependence of predicted uncertainties on different assumptions: inclusion of photometric galaxy clustering data, minimum angular scale taken into account, modelling of baryonic feedback effects. We conclude that the Euclid mission will be able to measure quantities related to the dark sector of particle physics with unprecedented sensitivity. This will provide important information for model building in high-energy physics. Any hint of a deviation from the minimal cold dark matter paradigm would have profound implications for cosmology and particle physics
Euclid: Early Release Observations -- Globular clusters in the Fornax galaxy cluster, from dwarf galaxies to the intracluster field
No full textInternational audienceWe present an analysis of Euclid observations of a 0.5 deg field in the central region of the Fornax galaxy cluster that were acquired during the performance verification phase. With these data, we investigate the potential of Euclid for identifying GCs at 20 Mpc, and validate the search methods using artificial GCs and known GCs within the field from the literature. Our analysis of artificial GCs injected into the data shows that Euclid's data in band is 80% complete at about mag ( mag), and resolves GCs as small as pc. In the band, we detect more than 95% of the known GCs from previous spectroscopic surveys and GC candidates of the ACS Fornax Cluster Survey, of which more than 80% are resolved. We identify more than 5000 new GC candidates within the field of view down to mag, about 1.5 mag fainter than the typical GC luminosity function turn-over magnitude, and investigate their spatial distribution within the intracluster field. We then focus on the GC candidates around dwarf galaxies and investigate their numbers, stacked luminosity distribution and stacked radial distribution. While the overall GC properties are consistent with those in the literature, an interesting over-representation of relatively bright candidates is found within a small number of relatively GC-rich dwarf galaxies. Our work confirms the capabilities of Euclid data in detecting GCs and separating them from foreground and background contaminants at a distance of 20 Mpc, particularly for low-GC count systems such as dwarf galaxies