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1.
Interpretation of the CALET Electron+Positron Spectrum concerning Dark Matter Signatures
Holger Motz, Yoichi Asaoka, Saptashwa Bhattacharyya, 2019, izvirni znanstveni članek

Opis: CALET (CALorimetric Electron Telescope) is in operation on the ISS since October 2015 and directly measures the electron+positron cosmic-ray spectrum up into the TeV-region with fine energy resolution and good proton rejection. Interpretations of the latest results published in [O. Adriani et al. PRL 120, 261102] regarding Dark Matter signatures are presented. Limits on annihilation and decay of Dark Matter were calculated based on an analytic parametrization of the local electron and positron spectra, including a term representing the flux from nearby pulsars as the extra electron-positron-pair source responsible for the positron excess, which is fitted to CALET data and positron flux/fraction data of AMS-02. The expected flux from Dark Matter is calculated with PYTHIA and DRAGON and added to the parametrization with increasing scale factor until reaching 95%CL exclusion, returning a limit on the annihilation cross-section or lifetime. By treating systematic uncertainties with known energy dependence as corrections to the fit function, limits were improved compared to all-random errors. Structures appear in the spectrum, which have been investigated as potential Dark Matter signatures by looking for an improvement of the fit quality with addition of flux from Dark Matter. Thereby, annihilation of ~350 GeV or decay of ~700 GeV Dark Matter to electron-positron pairs is identified as a possible explanation of a step-like structure around 350 GeV. The significance of this signature, Dark Matter explanations of other spectral features and possible astrophysical alternatives are discussed.
Ključne besede: Cosmic-rays, Dark Matter, CALET
Objavljeno v RUNG: 05.10.2023; Ogledov: 877; Prenosov: 5
.pdf Celotno besedilo (4,04 MB)
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2.
Searching for Anisotropy in Electron+Positron Cosmic Rays with CALET
Holger Motz, Yoichi Asaoka, Shoji Torii, Saptashwa Bhattacharyya, 2017, izvirni znanstveni članek

Opis: The ISS-based Calorimetric Electron Telescope (CALET) is directly measuring the energy spectrum and direction distribution of electron+positron cosmic-rays up to 20 TeV. A main goal of CALET is to identify a signature of a nearby supernova remnant (SNR) in electron+positron cosmic-rays. The Vela SNR has the highest potential to cause a spectral feature in the TeV region and/or a detectable anisotropy. Using the numerical cosmic-ray propagation code DRAGON, the spectrum and expected anisotropy of the Vela SNR together with background from more distant SNR was calculated depending on injection and propagation conditions. The results of these calculations were used to simulate CALET event sky-maps on which several analysis methods were employed to estimate the CALET sensitivity. Assuming that there is no anisotropy, the expected limits on the dipole amplitude from an all-sky search were calculated as a function of the selected energy range and the shape of the predicted spectra. However for the detection of a dipole anisotropy, the direction towards Vela is predetermined, and sensitivity is strongly boosted by a directed search. It is shown that with this method, CALET has a significant probability to identify an anisotropy signature from Vela. As it may disturb the Vela signature, the contribution to the local cosmic-ray anisotropy from several other nearby SNR and pulsars, as well as from the general source distribution in the galaxy was studied. It was found that Vela is expected to dominate and have a detectable signature, though there is some influence from other sources on direction and strength of the anisotropy. Furthermore, the implications of detecting an dipole anisotropy directed towards Vela for the local propagation parameters, such as the diffusion coefficient, are explained.
Ključne besede: cosmic-rays, CALET, cosmic-ray propagation
Objavljeno v RUNG: 05.10.2023; Ogledov: 702; Prenosov: 4
.pdf Celotno besedilo (7,60 MB)
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3.
Searching for cosmic-ray signals from decay of fermionic dark matter with CALET
Saptashwa Bhattacharyya, Holger Motz, Shoji Torii, Yoichi Asaoka, 2017, objavljeni znanstveni prispevek na konferenci

Ključne besede: dark matter, cosmic-rays, CALET
Objavljeno v RUNG: 08.02.2021; Ogledov: 2207; Prenosov: 0
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4.
An interpretation of the cosmic ray e + + e − spectrum from 10 GeV to 3 TeV measured by CALET on the ISS
Saptashwa Bhattacharyya, 2019, izvirni znanstveni članek

Ključne besede: CALET, cosmic rays, dark matter
Objavljeno v RUNG: 06.01.2021; Ogledov: 2250; Prenosov: 0
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