Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E10: Cosmic Ray Sources and AccelerationLive
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Sponsoring Units: DAP Chair: Alexander Moiseev, UMD |
Saturday, April 17, 2021 3:45PM - 3:57PM Live |
E10.00001: SuperTIGER Abundances of Galactic Cosmic Rays for the Atomic Number (Z) Interval 30 to 56 Nathan Walsh We report preliminary elemental abundance results from the 55-day long-duration-balloon flight of SuperTIGER (Super Trans-Iron Galactic Element Recorder) during the 2012-2013 austral summer. SuperTIGER measured the relative abundances of Galactic cosmic-ray (GCR) nuclei with high statistical precision and well resolved individual element peaks from $_{10}$Ne to $_{40}$Zr. SuperTIGER also made exploratory measurements of the relative abundances up to $_{56}$Ba. Although the statistics are low for elements heavier than $_{40}$Zr, we present preliminary relative abundance measurements of charges $Z=41-56$ with individual element resolution. GCR measurements up to $_{40}$Zr support a source acceleration model where supernovae in OB associations preferentially accelerate refractory elements that are more readily embedded in interstellar dust grains than volatiles. In addition, injection into the GCR for both refractory and volatile elements appears to follow a charge dependence consistent with their grain sputtering cross sections. Our preliminary measurements of the $Z=41-56$ range suggest the existence of an alternative GCR source or acceleration model for $Z>40$ elements. [Preview Abstract] |
Saturday, April 17, 2021 3:57PM - 4:09PM Live |
E10.00002: Steep Cosmic Ray Spectra in Supernova Remnants Rebecca Diesing, Damiano Caprioli Galactic cosmic rays (CRs) are accelerated at the forward shocks of supernova remnants (SNRs) via diffusive shock acceleration (DSA), an efficient acceleration mechanism that predicts power-law energy distributions of CRs. However, observations of nonthermal SNR emission imply CR energy distributions that are generally steeper than $E^{-2}$, the standard DSA prediction. Recent results from hybrid simulations suggest that such steep spectra may arise from the motion of magnetic structures with respect to the thermal plasma downstream of the shock. Using the Cosmic Ray Analytical Fast Tool (CRAFT), a semi-analytic model of non-linear DSA, we generalize this result to a wide range of SNRs. By accounting for the motion of magnetic structures in the downstream, we produce CR energy distributions that are substantially steeper than $E^{-2}$ and consistent with observations of a wide range of SNRs. Our formalism reproduces both the modestly steep spectra of historical supernova remnants ($\propto E^{-2.2}$) and the very steep spectra of young radio supernovae ($\propto E^{-3}$). [Preview Abstract] |
Saturday, April 17, 2021 4:09PM - 4:21PM Live |
E10.00003: Composition study of cosmic rays using machine-learning at the IceCube Neutrino Observatory Matthias Plum, Karen Andeen The IceCube Neutrino Observatory at the South Pole is a multi-component detector capable of measuring cosmic rays in the energy range from PeV to EeV. This energy region is typically thought to cover the transition from galactic to extragalactic sources. The IceTop array at the surface is sensitive to the electromagnetic part of an air shower while the deep in-ice array detects the high-energy (TeV) muonic component. By applying modern machine-learning and statistical methods to reconstructed cosmic-ray air showers passing through both arrays, the primary energy and the composition can be simultaneously measured. In this contribution, we will discuss the reconstruction technique and composition sensitivity of IceCube observables presently under development for future detector enhancements of IceCube Observatory. [Preview Abstract] |
Saturday, April 17, 2021 4:21PM - 4:33PM Live |
E10.00004: Testing Charge-, Sign- and Energy-Dependence of Cosmic-Ray Solar Modulation with AMS-02 Observations During Cycles 23 and 24 Ian McKinnon, Ilias Cholis, Dan Hooper, Tim Linden Our basic theoretical understanding of the sources of cosmic rays and their propagation through the interstellar medium is hindered by the Sun, that through the solar wind affects the observed cosmic-ray spectra. This effect is known as solar modulation. However recently released cosmic-ray data and publicly available measurements of the solar wind properties from ACS and the Wilcox observatory allow us to test the analytical modeling of the time-, charge- and energy-dependence of solar modulation. Using the well-established time-dependence of solar modulation we find evidence for its charge and energy dependence. [Preview Abstract] |
Saturday, April 17, 2021 4:33PM - 4:45PM Live |
E10.00005: The Imprint of Large Scale Structure on the Ultra-High-Energy Cosmic Ray Sky Chen Ding, Noemie Globus, Glennys Farrar We show how to use the large- and intermediate-angular-scale anisotropies of ultra-high-energy cosmic rays (UHECRs) observed by the Pierre Auger Observatory to infer the origin and composition of UHECRs. A good accounting of the magnitude, direction and energy dependence of the dipole anisotropy at energies above 8 EeV is obtained, with the postulation that the source distribution follows the matter distribution of the local Universe, and taking into account the impact of energy losses during propagation and deflections in the Galactic magnetic field. The observed dipole anisotropy is incompatible with a pure proton composition in this scenario. We demonstrate the importance of the accuracy of the treatment of energy losses, and we present the improved treatment which unleashes the power of the model in constraining the UHECR composition and properties of the extragalactic and Galactic magnetic fields, and potentially exposing individual UHECR sources in future updates. [Preview Abstract] |
Saturday, April 17, 2021 4:45PM - 4:57PM Live |
E10.00006: Ab-initio Simulations of Cosmic Ray Escape from Their Sources Damiano Caprioli, Benedikt Schroer, Oreste Pezzi, Colby Haggerty, Pasquale Blasi We explore the escape of energetic cosmic rays (CRs) from their sources via hybrid (kinetic protons-fluid electrons) plasma simulations. For the first time, we self-consistently find that the excitation of streaming instabilities leads to enhanced CR diffusivity and in turn to a large pressure gradient that causes the formation of expanding bubbles of gas and self-generated magnetic fields. This phenomenon is general and is expected to occur around any sufficiently powerful CR source in the Galaxy. Our results provide a theoretical framework for explaining recent observations of gamma-ray haloes around supernova remnants, stellar clusters and pulsar wind nebulae, which are interpreted as regions where the diffusion coefficient is 10-100 times smaller than the typical Galactic one. Finally, we outline the potential role of such regions for the feedback that CRs may exert on star formation. [Preview Abstract] |
Saturday, April 17, 2021 4:57PM - 5:09PM Live |
E10.00007: The Kinetic Plasma Physics of Cosmic Ray Streaming Instabilities: Hybrid Simulations of the Nonlinear Growth Colby Haggerty, Damiano Caprioli, Ellen Zweibel Cosmic Rays (CRs) are believed to amplify magnetic fields and heat thermal plasma throughout the galaxy via streaming instability. Both theoretical and numerical models of galaxy formation are sensitive to small changes in these plasma parameters, however most of the scientific understanding of the effects of CR streaming instabilities comes from analytical linear theory. We detail the linear and nonlinear effects of both the resonant and nonresonant (Bell) streaming instability using the relativistic kinetic hybrid code, dHybridR. ``Undriven'' simulations (i.e., where CRs are not continuously supplied) agree well with linear theory for a range of wave numbers but with several novel nonlinear features. Additionally, we examine the ``driven'' case (sustained CR injection) in which nonlinear effects are important as the background plasma begins to be heated and pushed, leading to the saturation of the instability. Finally, we extract from the simulations heating rates and self-generated diffusion coefficients, which can be implemented into galaxy formation models. [Preview Abstract] |
Saturday, April 17, 2021 5:09PM - 5:21PM Live |
E10.00008: Saturation of the Non-Resonant Cosmic Ray Streaming Instability Siddhartha Gupta, Georgios Zacharegkas, Colby Haggerty, Damiano Caprioli We perform both fully-kinetic and hybrid (kinetic protons-fluid electrons) plasma simulations to study the saturated amplified magnetic fields produced by the non-resonant (or Bell) instability driven by energetic particles (cosmic rays, CRs). Using a survey of 1D, 2D and 3D simulations, we connect initial plasma and CR parameters to the strength of the magnetic fields at saturation. A simple analytic theory is derived for such a saturation, which agrees well with the simulations. These results are important for understanding CR acceleration and transport in astrophysical systems, as well as beam-driven instabilities in laboratory experiments. [Preview Abstract] |
Saturday, April 17, 2021 5:21PM - 5:33PM Live |
E10.00009: Using Convolutional Neural Networks for the Classification of Radio Signals from Cosmic-Ray Air Showers. Abdul Rehman, Frank Schroeder, Alan Coleman In the past two decades, radio experiments around the world have shown that radio detection of cosmic-ray air showers is an effective and inexpensive technique for measuring the properties of primary cosmic rays: properties like the energy, direction, and composition of primary particles which can help us understand the exotic processes going on in the galactic and extragalactic objects. The irreducible Galactic and thermal backgrounds pose a significant challenge for radio detection of air showers. In an effort to improve the detection threshold, we want to mitigate the background by using machine learning techniques, namely convolutional neural networks. Inspired by previous work at Tunka-Rex, we test two different networks: a Classifier which would enable us to distinguish the radio signal traces from the pure background, and a Denoiser which will help us to recover the underlying cosmic-ray signal from the background. For training and testing of the network, we use simulations to generate radio signals from air showers in addition to modeled and measured background. These networks, once trained, will enable us to lower the detection threshold of radio experiments at Antarctica and to better reconstruct the properties of primary cosmic rays. [Preview Abstract] |
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