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SPECTROSCOPIE DES RAIES SOLAIRES AVEC UN CAPTEUR A FILTRES COLORES RVVB DE BAYER, QUELQUES LIMITATIONS
No full textNous étudions dans cet article les possibilités des capteurs à filtres colorés RVVB de Bayer en spectroscopie des raies solaires de la photosphère et de la chromosphère et présentons les principales limitations. La spectroscopie produisant une lumière quasi monochromatique, le choix d'un capteur monochrome (sensible à l'intensité de la lumière) s'impose naturellement ; néanmoins, nous verrons que l'emploi d'un capteur recouvert d'un filtre RVVB de Bayer est exploitable en spectroscopie si l'on accepte de perdre du flux et un facteur deux en résolution spatiale et spectrale
Euclid VI. NISP-P optical ghosts
No full textInternational audienceThe Near-Infrared Spectrometer and Photometer (NISP) onboard Euclid includes several optical elements in its path, which introduce artefacts into the data from non-nominal light paths. To ensure uncontaminated source photometry, these artefacts must be accurately accounted for. This paper focuses on two specific optical features in NISP's photometric data (NISP-P): ghosts caused by the telescope's dichroic beamsplitter, and the bandpass filters within the NISP fore-optics. Both ghost types exhibit a characteristic morphology and are offset from the originating stars. The offsets are well modelled using 2D polynomials, with only stars brighter than approximately 10 magnitudes in each filter producing significant ghost contributions. The masking radii for these ghosts depend on both the source-star brightness and the filter wavelength, ranging from 20 to 40 pixels. We present the final relations and models used in the near-infrared (NIR) data pipeline to mask these ghosts for Euclid's Quick Data Release (Q1)
Effect of the Kinetic Temperature of Plasma Electrons on Dispersion and Rotation Measures
No full textInternational audienceThe aim of this work is to analyze the impact of the kinetic temperature of electrons in a warm anisotropic plasma and the strength of its magnetic field on the integral characteristics of pulsar pulsed radio emission propagation, such as the dispersion measure (DM) and rotation measure (RM). An important aspect in this context is the presence of magnetic fields in the plasma, their strength, and their configuration relative to the line of sight. The approach uniquely accounts for polarization splitting into ordinary and extraordinary waves in pulsar pulsed radio emission and considers the limiting cases of quasi-longitudinal and quasi-transverse propagation of these waves in a medium with magnetic fields of various strengths, with or without scattering. This makes it possible to predict a possible dependence of the DM and RM on frequency (not previously anticipated), magnetic field strength, and electron kinetic temperature as well as the amplification of this dependence with increasing magnetic field strength. Notably, the frequency dependence of the DM and RM is more pronounced at low frequencies, with both measures increasing as frequency decreases. Accounting for these dependences when analyzing DM and RM toward different pulsars makes it possible to estimate cosmic magnetoactive plasma parameters, including the range of electron kinetic temperatures and the strengths of longitudinal and transverse magnetic field components along the path of polarized radiation propagation. Thus, using pulsar pulses as probing radio emission makes it possible to study warm magnetoactive plasma with magnetic field strengths of the order of 1–10 G or higher, such as the solar corona, the Jupiter–Io flux tube, and the Earth's ionosphere
Spatial and Temporal Evaluations of the Liquid Argon Purity in ProtoDUNE-SP
No full textInternational audienceLiquid argon time projection chambers (LArTPCs) rely on highly pure argon to ensure that ionization electrons produced by charged particles reach readout arrays. ProtoDUNE Single-Phase (ProtoDUNE-SP) was an approximately 700-ton liquid argon detector intended to prototype the Deep Underground Neutrino Experiment (DUNE) Far Detector Horizontal Drift module. It contains two drift volumes bisected by the cathode plane assembly, which is biased to create an almost uniform electric field in both volumes. The DUNE Far Detector modules must have robust cryogenic systems capable of filtering argon and supplying the TPC with clean liquid. This paper will explore comparisons of the argon purity measured by the purity monitors with those measured using muons in the TPC from October 2018 to November 2018. A new method is introduced to measure the liquid argon purity in the TPC using muons crossing both drift volumes of ProtoDUNE-SP. For extended periods on the timescale of weeks, the drift electron lifetime was measured to be above 30 ms using both systems. A particular focus will be placed on the measured purity of argon as a function of position in the detector
Gaps in stellar streams as a result of globular cluster flybys. The case of Palomar 5
No full textInternational audienceContext. Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. The literature commonly interprets the presence of underdensity regions, or gaps, along these streams as being due to the close passage of dark matter subhalos. Aims. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream generated by a cluster with characteristics (mass, size, and orbit) similar to those of Palomar 5, a well-known globular cluster in the Galactic halo that has particularly long tidal tails. Methods. For this purpose, we used a particle-test code to simulate the formation and evolution of the stream when subjected to the Galaxy's gravitational field plus its whole system of globular clusters. Results. Our study shows that such a stream can be strongly perturbed by the close passage of other clusters, in particular NGC 2808, NGC 7078, and NGC 104, and that these perturbations induce the formation of gaps in the tails. Conclusions. The results of this work show that globular clusters can induce gaps in cold streams-just as it has been demonstrated in the literature for that other baryonic components, such as giant molecular clouds and the Galactic bar. Therefore, a future work that attempts to infer the dark matter subhalo distribution from stellar stream gaps must include the contributions from globular clusters.</div
H.E.S.S. programme searching for VHE gamma rays associated with FRBs
No full textInternational audienceFast Radio Bursts (FRBs) are highly energetic, extremely short-lived bursts of radio flashes. Despite extensive research, the exact cause of these outbursts remains speculative. The high luminosity, short duration, and high dispersion measure of these events suggest they result from extreme, high-energy extragalactic sources, such as highly magnetized and rapidly spinning neutron stars known as magnetars. The number of detected FRBs, including repeating ones, has grown rapidly in recent years. Except for FRB 20200428D, and FRB-like radio burst that is associated to Galactic magnetar SGR 1935+2154, no multi-wavelength counterpart to any FRB has been detected yet. The High Energy Stereoscopic System (H.E.S.S.) telescope has developed a {program} to follow up FRBs searching for their gamma-ray counterparts, helping to uncover the nature of FRBs and FRB sources. This paper provides an overview of the searches for FRB sources conducted by H.E.S.S., including follow-up observations and simultaneous multi-wavelength campaigns with radio and X-ray observatories. Among the FRB sources observed by H.E.S.S., nine are localized with redshifts ranging between 0.11 and 0.492 from 2015 to 2022. No significant very high energy (VHE) emission was detected during these observations. We report constraints on the VHE luminosity ranging from erg s and erg s, placing limits on the FRB's region persistent VHE emission and potential FRB afterglow emission across timescales from hours to years
Revision of conservative lower bound on intergalactic magnetic field from Fermi and Cherenkov telescope observations of extreme blazars
No full textInternational audienceJoint observations of extreme blazars with Fermi Large Area Telescope (LAT) and Imaging Atmospheric Cherenkov telescopes (IACT) have been previously used to derive lower bounds on intergalactic magnetic field (IGMF). We update these previous bounds using a set of extreme blazars that are detected in the Very-High-Energy (VHE, photon energies above 100 GeV) band by both Fermi/LAT and IACTs. We measure IGMF-dependent suppression of secondary delayed gamma-ray flux from electron-positron pairs deposited in the intergalactic medium by VHE gamma-rays interacting with Extragalactic Background Light. From overall 22 extreme blazars detected by Fermi/LAT and IACTs in the VHE band, seven have their spectral characteristics inconsistent with the possibility of zero magnetic field along their lines of sight, even under the most restrictive assumption that the sources have only switched on at the start of VHE band observations. Adopting this assumption, we derive a "conservative" lower bound on the IGMF strength at the level of 2e-17 G. The tightest bound is imposed by the signal of 1ES 0502+675, a source that has not been considered in the IGMF analysis before. Our bound is comparable to the bound derived by MAGIC collaboration, but is weaker than that previously derived from analysis of Fermi/LAT and HESS telescope data, even though our dataset includes that data. We clarify the origin of this discrepancy
Probing the Higgs boson CP properties in vector-boson fusion production in the channel with the ATLAS detector
No full textInternational audienceThe CP properties of the Higgs boson are studied in the vector-boson fusion production mode. The analysis exploits the decay mode of the Higgs boson into two -leptons using 140 fb of proton-proton collision data at TeV collected by the ATLAS experiment at the Large Hadron Collider. Results are obtained using the Optimal Observable method. CP-violating interactions between the Higgs boson and electroweak gauge bosons are considered in the effective field theory framework, with the interaction strength described in the HISZ basis by , and in the Warsaw basis by , , and . No deviations relative to the Standard Model are observed, and limits are obtained on the strength parameters. The parameter is constrained to the interval [] at the 95% confidence level while is constrained to [], when considering both linear and quadratic effects of physics beyond the Standard Model
PrAICC: A Predictible Inter-Core Communication Model for AMP systems
No full textInternational audienc
The birth of Be star disks: I. From localized ejection to circularization
No full textInternational audienceContext. Classical Be stars are well known to eject mass to build up a disk, but the details governing the initial distribution and subsequent evolution of this matter into a disk are in general poorly constrained through observations.Aims. By combining high-cadence time-series spectroscopy with contemporaneous space photometry from the Transiting Exoplanet Survey Satellite (TESS), we have sampled about 30 mass ejection events in 13 Be stars. Our goal is to constrain the geometrical and kinematic properties of the ejecta as early as possible, facilitating the investigation into the material's initial conditions and evolution, and understanding its interactions with preexisting material.Methods. The photometric variability is analyzed together with measurements of the at-times rapidly changing emission features in order to identify the onset of outburst events and obtain information about the geometry of the ejecta and how it changes over time. Short-lived line asymmetries display oscillation cycles (Štefl frequencies), which are compared to photometric and stable spectroscopic frequencies.Results. All Be stars observed with sufficiently high cadence during an outburst are found to exhibit rapid oscillations of line asymmetry with a single frequency in the days following the start of the event. For a given star this circumstellar frequency may differ only slightly from event to event even when the outbursts they are associated with have different properties. These circumstellar frequencies are typically between 0.5 to 2 d−1, and are generally near photometric frequencies. They are slightly below prominent (generally stable) spectroscopic frequencies seen in photospheric absorption lines. The emission asymmetry cycles break down after roughly 5–10 cycles, with the emission line profile converging toward approximate symmetry shortly thereafter. In photometry, several frequencies typically emerge at relatively high amplitude at some point during the mass ejection process.Conclusions. In all observed cases, freshly ejected material was initially constrained within a narrow azimuthal range, indicating it was launched from a localized region on the stellar surface. The material orbits the star with a frequency consistent with the near-surface Keplerian orbital frequency. This material circularizes into a disk configuration after several orbital timescales. This is true whether or not there was a preexisting disk at the time of the observed outburst. We find no evidence for precursor phases prior to the ejection of mass in our sample. The several photometric frequencies that emerge during outburst are at least partially stellar in origin