Using cosmic-ray boron to carbon ratio (B/C) data recently released by the Ams-02 experiment, we find indications (decisive evidence, in Bayesian terms) in favor of a diffusive propagation origin for ...the broken power-law spectra found in protons (p) and helium nuclei (He). The result is robust with respect to currently estimated uncertainties in the cross sections, and in the presence of a small component of primary boron, expected because of spallation at the acceleration site. Reduced errors at high energy as well as further cosmic ray nuclei data (as absolute spectra of C, N, O, Li, Be) may definitively confirm this scenario.
Abstract
Gamma-ray astronomy has become one of the main experimental ways to test the modified dispersion relations (MDRs) of photons in vacuum, obtained in some attempts to formulate a theory of ...quantum gravity. The MDRs in use imply time delays that depend on the energy and that increase with distance following some function of redshift. The use of transient, or variable, distant and highly energetic sources already allows us to set stringent limits on the energy scale related to this phenomenon, usually thought to be of the order of the Planck energy, but robust conclusions on the existence of MDR-related propagation effects still require the analysis of a large population of sources. In order to gather the biggest sample of sources possible for MDR searches at teraelectronvolt energies, the H.E.S.S., MAGIC, and VERITAS collaborations enacted a joint task force to combine all their relevant data to constrain the quantum gravity energy scale. In the present article, the likelihood method used to combine the data and provide a common limit is described in detail and tested through simulations of recorded data sets for a gamma-ray burst, three flaring active galactic nuclei, and two pulsars. Statistical and systematic errors are assessed and included in the likelihood as nuisance parameters. In addition, a comparison of two different formalisms for distance dependence of the time lags is performed for the first time. In a second article, to appear later, the method will be applied to all relevant data from the three experiments.
The constituents of soft matter systems such as colloidal suspensions, emulsions, polymers, and biological tissues undergo microscopic random motion, due to thermal energy. They may also experience ...drift motion correlated over mesoscopic or macroscopic length scales, e.g. in response to an internal or applied stress or during flow. We present a new method for measuring simultaneously both the microscopic motion and the mesoscopic or macroscopic drift. The method is based on the analysis of spatio-temporal cross-correlation functions of speckle patterns taken in an imaging configuration. The method is tested on a translating Brownian suspension and a sheared colloidal glass.
In this work, we describe the optical properties of the single photoelectron (SPE) calibration system designed for NectarCAM, a camera proposed for the Medium Sized Telescopes (MST) of the Cherenkov ...Telescope Array (CTA). One of the goals of the SPE system, as integral part of the NectarCAM camera, consists in measuring with high accuracy the gain of its photo-detection chain. The SPE system is based on a white painted screen where light pulses are injected through a fishtail light guide from a dedicated flasher. The screen – placed 15 mm away from the focal plane – is mounted on an XY motorization that allows movements over all the camera plane. This allows in-situ measurements of the SPE spectra via a complete scan of the 1855 photo-multiplier tubes (PMTs) of NectarCAM. This calibration process will enable the reduction of the systematic uncertainties on the energy reconstruction of γ-rays coming from distant astronomical sources and detected by CTA.
We discuss the design of the screen used in the calibration system and we present its optical performances in terms of light homogeneity and timing of the signal.
AMS-02 est un spectromètre magnétique conçu pour la détection du rayonnement cosmique chargé et des photons gamma. La mesure en 2013 de la fraction de positons par AMS-02 a confirmé la présence d'une ...composante de positons primaires, nécessitant l'existence d'une source de positons dans notre Galaxie. Cette thèse s'est exclusivement consacrée à l'étude de ce phénomène, et à la recherche de cette source de positons. La fraction de positons, le flux de positons et le flux d'électrons sont mesurés à l'aide d'une méthode de fit multidimensionnel mis au point lors de cette thèse. Une étude particulière est réservé au phénomène de confusion de charge, important pour la mesure du signe de la charge à haute énergie. La fonction de réponse instrumentale du détecteur est évaluée à l'aide de simulations Monte Carlo et est corrigée par les données réelles du détecteur. Un travail phénoménologique est effectué afin d'interpréter les résultats mesurés. L'interprétation de ces résultats en termes de composante primaire issues d'un pulsar local et du halo galactique de matière noire est effectué. Les implications et l'espace des paramètres autorisé pour chacun des modèles est explicité. Une ré-évaluation des secondaires à l'aide des nouvelles données d'AMS-02, ainsi que l'étude de l'impact de l'erreur expérimentale d'AMS-02 sur ces résultats, est exécuté.
AMS-02 is a magnetic spectrometer design for the cosmic ray and gamma ray detection. The measurement in 2013 of the positron fraction by AMS-02 confirmed the presence of a primary positron component, which means the existence of a galactic primary source of positrons. This thesis is devoted exclusively to the study of this phenomenon. The positron fraction, the positron flux, and the electron flux are measured using a method of multidimensional fit developed during this thesis. The charge confusion phenomenon, which is important at the highest energies, is investigated. The instrumental response function of the detector is evaluated using Monte Carlo simulations and is corrected using the ISS data. A phenomenological work is done to interpret the measured results. The interpretation of these results in terms of primary component from a local pulsar and dark matter halo is done. The implications and the parameter space allowed for each model is detailed. A reevaluation of secondaries with the new AMS-02 data, and the study of the impact of the experimental error of AMS-02 on these results is performed.
The Cherenkov Telescope Array Observatory (CTAO) is the next generation of observatories employing the imaging air Cherenkov technique for the study of very high energy gamma rays. The deployment of ...deep learning methods for the reconstruction of physical attributes of incident particles has evinced promising outcomes when conducted on simulations. However, the transition of this approach to observational data is accompanied by challenges, as deep learning-based models are susceptible to domain shifts. In this paper, we integrate domain adaptation in the physics-based context of the CTAO and shed light on the gain in performance that these techniques bring using LST-1 real acquisitions.
The Large-Sized Telescopes (LSTs) of the Cherenkov Telescope Array Observatory (CTAO) will play a crucial role in the study of transient gamma-ray sources, such as gamma-ray bursts and flaring active ...galactic nuclei. The low energy threshold of LSTs makes them particularly well suited for the detection of these phenomena. The ability to detect and analyze gamma-ray transients in real-time is essential for quickly identifying and studying these rare and fleeting events. In this conference, we will present recent advances in the real-time analysis of data from the LST-1, the first prototype of LST located in the Canary island of La Palma. We will discuss in particular the development of new algorithms for event reconstruction and background rejection. These advances will enable rapid identification and follow-up observation of transient gamma-ray sources, making the LST-1 a powerful tool for the study of the dynamic universe. The implementation of this framework in the future Array Control and Data Acquisition System (ACADA) of CTAO will be discussed as well, based on the experience with LST.
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