Explaining Tev Cosmic-Ray Anisotropies With Non-Diffusive Cosmic-Ray Propagation

Harding, J. Patrick; Fryer, Chris L.; Mendel, Susan

doi:10.3847/0004-637x/822/2/102

Cited by 15 publications

(35 citation statements)

References 50 publications

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“…Scattering processes with stochastic magnetic instabilities produce perturbations in the arrival directions within the scattering mean free path. Such perturbations may be observed as stochastic localized excess or deficit regions (Giacinti and Sigl, 2012;Biermann et al, 2013;Ahlers, 2014;Ahlers and Mertsch, 2015;Ló pez-Barquero et al, 2016a;Harding et al, 2016;Scherer et al, 2016).…”

Section: Anisotropy Of Local Cosmic Raysmentioning

confidence: 99%

Astrophysical neutrinos and cosmic rays observed by IceCube

Aartsen¹,

Ackermann²,

Adams³

et al. 2018

Advances in Space Research

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The core mission of the IceCube neutrino observatory is to study the origin and propagation of cosmic rays. IceCube, with its surface component IceTop, observes multiple signatures to accomplish this mission. Most important are the astrophysical neutrinos that are produced in interactions of cosmic rays, close to their sources and in interstellar space. IceCube is the first instrument that measures the properties of this astrophysical neutrino flux and constrains its origin. In addition, the spectrum, composition, and anisotropy of the local cosmic-ray flux are obtained from measurements of atmospheric muons and showers. Here we provide an overview of recent findings from the analysis of IceCube data, and their implications to our understanding of cosmic rays.

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Section: Anisotropy Of Local Cosmic Raysmentioning

confidence: 99%

Astrophysical neutrinos and cosmic rays observed by IceCube

Aartsen¹,

Ackermann²,

Adams³

et al. 2018

Advances in Space Research

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“…Solving Equation 9 is computationally expensive because of the number of directional changes the particle makes. Therefore, the code makes the common approximation that the particle simply follows the magnetic field line that it experiences (Harding et al 2016;Fitz Axen et al 2021). This is a valid approximation as long as r g changes on a much smaller scale than the magnetic field because of the assumption that solving Equation 9 would be unlikely to move the particle into a region with a different magnetic field.…”

Section: Methodsmentioning

confidence: 99%

“…If it does, the particle travels only to the edge of the cell, even if this distance is less than ∆x. When it enters a new cell its path length and travel distance are resampled and its motion continues along the previously determined direction (Harding et al 2016;Fitz Axen et al 2021).…”

Section: Methodsmentioning

confidence: 99%

Transport of Protostellar Cosmic Rays in Turbulent Dense Cores

Axen,

Offner,

Gaches

et al. 2021

Preprint

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Recent studies have suggested that low-energy cosmic rays (CRs) may be accelerated inside molecular clouds by the shocks associated with star formation. We use a Monte Carlo transport code to model the propagation of CRs accelerated by protostellar accretion shocks through protostellar cores. We calculate the CR attenuation and energy losses and compute the resulting flux and ionization rate as a function of both radial distance from the protostar and angular position. We show that protostellar cores have non-uniform CR fluxes that produce a broad range of CR ionization rates, with the maximum value being up to two orders of magnitude higher then the radial average at a given distance. In particular, the CR flux is focused in the direction of the outflow cavity, creating a 'flashlight' effect and allowing CRs to leak out of the core. The radially averaged ionization rates are less than the measured value for the Milky Way of ζ ≈ 10 −16 s −1 ; however, within r ≈ 0.03 pc from the protostar, the maximum ionization rates exceed this value. We show that variation in the protostellar parameters, particularly in the accretion rate, may produce ionization rates that are a couple of orders of magnitude higher or lower than our fiducial values. Finally, we use a statistical method to model unresolved sub-grid magnetic turbulence in the core. We show that turbulence modifies the CR spectrum and increases the uniformity of the CR distribution but does not significantly affect the resulting ionization rates.

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“…In fact, small-scale anisotropies have been the subject of intensive research not only observationally but also theoretically. Many different scenarios have been proposed to explain the presence of anisotropies at small angular scales which includes, for example, effects of the heliosphere (Drury 2013;Zhang et al 2014;Schwadron et al 2014), non-uniform pitch-angle diffusion (Malkov et al 2010), non-diffusive propagation of Galactic CRs (Battaner et al 2011;Harding et al 2016), and also more exotic explanations (Kotera et al 2013).…”

Section: Introductionmentioning

confidence: 99%

No longer ballistic, not yet diffusive--the formation of cosmic ray small-scale anisotropies

Kuhlen,

Phan,

Mertsch

2021

Preprint

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The arrival directions of TeV-PeV cosmic rays are remarkably uniform due to the isotropization of their directions by scattering on turbulent magnetic fields. Small anisotropies can exist in standard diffusion models, however, only on the largest angular scales. Yet, high-statistics observatories like IceCube and HAWC have found significant deviations from isotropy down to small angular scales. Here, we explain the formation of small-scale anisotropies by considering pairs of cosmic rays that get correlated by their transport through the same realisation of the turbulent magnetic field. We argue that the formation of small-scale anisotropies is the reflection of the particular realisation of the turbulent magnetic field experienced by cosmic rays on time scales intermediate between the early, ballistic regime and the late, diffusive regime. We approach this problem in two different ways: First, we run test particle simulations in synthetic turbulence, covering for the first time the TV rigidities of observations with realistic turbulence parameters. Second, we extend the recently introduced mixing matrix approach and determine the steady-state angular power spectrum. Throughout, we adopt magneto-static, slab-like turbulence. We find excellent agreement between the predicted angular power spectra in both approaches over a large range of rigidities. In the future, measurements of small-scale anisotropies will be valuable in constraining the nature of the turbulent magnetic field in our Galactic neighborhood.

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Explaining Tev Cosmic-Ray Anisotropies With Non-Diffusive Cosmic-Ray Propagation

Cited by 15 publications

References 50 publications

Astrophysical neutrinos and cosmic rays observed by IceCube

Astrophysical neutrinos and cosmic rays observed by IceCube

Transport of Protostellar Cosmic Rays in Turbulent Dense Cores

No longer ballistic, not yet diffusive--the formation of cosmic ray small-scale anisotropies

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