The Large-Scale Cosmic-Ray Anisotropy as Observed With Milagro

Abdo, A. A.; Allen, B.; Aune, T.; Berley, D.; Casanova, S.; Chen, C.; Dingus, B. L.; Ellsworth, R. W.; Fleysher, Lazar; Fleysher, Roman; González, M. M.; Goodman, J. A.; Hoffman, C. M.; Hopper, B. J.; Hüntemeyer, P.; Kolterman, B. E.; Lansdell, C. P.; Linnemann, J.; McEnery, J. E.; Mincer, A. I.; Némethy, P.; Noyes, D.; Pretz, J.; Ryan, J. M.; Parkinson, P. M. Saz; Shoup, A.; Sinnis, G.; Smith, A. J.; Sullivan, G. W.; Vasileiou, V.; Walker, G.; Williams, D. A.; Yodh, G.

doi:10.1088/0004-637x/698/2/2121

Cited by 187 publications

(193 citation statements)

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“…The anisotropy of the arrival direction of the cosmic-rays, which was first detected by Milagro [13], and later on confirmed by other experiments like IceCube [14], has been also observed with HAWC [15]. The left panel of Figure 5 shows the cosmic ray sky map obtained with 113 days of HAWC-100 (HAWC detector with 100 WCD) data.…”

Section: Scientific Resultssupporting

confidence: 68%

First year results from the HAWC observatory

Casanova

2017

EPJ Web Conf.

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Abstract. The High Altitude Water Cherenkov Observatory is an all-sky surveying instrument sensitive to gamma rays and cosmic rays from 100GeV to 100TeV. With its 2sr instantaneous field of view and a duty cycle of > 95%, HAWC is carrying out an unbiased survey of the Northern sky and is monitoring known flaring sources and searching for transients. HAWC operation began mid-2013 with a partially-completed detector. The array was terminated in 2015. We here summarize the status of the observatory, and highlight its first scientific results, resulting from the first year of data taking after completion of the detector. In particular, we will present the HAWC map of the sky at tens of TeV.

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Section: Scientific Resultssupporting

confidence: 68%

First year results from the HAWC observatory

Casanova

2017

EPJ Web Conf.

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“…Due to scattering in magnetic fields, the anisotropy imprinted upon the distribution of arrival directions is mainly expected at large scales up to the highest energies. Large-scale patterns with anisotropy contrast at the level of 10 −4 to 10 −3 have been reported by several experiments for energies below 10 15 eV where the high flux of cosmic rays allows the collection of a large number of events (Amenomori et al 2005;Guillian et al 2007;Aglietta et al 2009;Abdo et al 2009;Abbasi et al 2010Abbasi et al , 2011Abbasi et al , 2012Aartsen et al 2013). For energies above a few 10 15 eV, the decrease of the flux with energy makes it challenging to collect the necessary statistics required to reveal amplitudes down to 10 −3 or 10 −2 .…”

Section: Introductionmentioning

confidence: 84%

SEARCHES FOR LARGE-SCALE ANISOTROPY IN THE ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE ENERGY OF 10¹⁹eV AT THE PIERRE AUGER OBSERVATORY AND THE TELESCOPE ARRAY

Aab

Abreu

Aglietta

et al. 2014

ApJ

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Spherical harmonic moments are well-suited for capturing anisotropy at any scale in the flux of cosmic rays. An unambiguous measurement of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data from observatories located in both the northern and southern hemispheres. To this end, a joint analysis using data recorded at the Telescope Array and the Pierre Auger Observatory above 10 19 eV is presented in this work. The resulting multipolar expansion of the flux of cosmic rays allows us to perform a series of anisotropy searches, and in particular to report on the angular power spectrum of cosmic rays above 10 19 eV. No significant deviation from isotropic expectations is found throughout the analyses performed. Upper limits on the amplitudes of the dipole and quadrupole moments are derived as a function of the direction in the sky, varying between 7% and 13% for the dipole and between 7% and 10% for a symmetric quadrupole.

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“…Cosmic ray anisotropies up to the level of one-per-mille have been observed at various energies by the observatories Tibet AS-γ [6,7], Super-Kamiokande [8], Milagro [9,10], ARGO-YBJ [11,12], EAS-TOP [13], IceCube [14][15][16] and HAWC [17]. The explanation of the strength and phase of the observed dipole anisotropy is challenging, but is qualitatively consistent with the diffusive prediction [4].…”

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confidence: 99%

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields

Ahlers

2014

Phys. Rev. Lett.

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The propagation of cosmic rays (CRs) in turbulent interstellar magnetic fields is typically described as a spatial diffusion process. This formalism predicts only a small deviation from an isotropic CR distribution in the form of a dipole in the direction of the CR density gradient or relative background flow. We show that the existence of a global CR dipole moment necessarily generates a spectrum of higher multipole moments in the local CR distribution. These anomalous anisotropies are a direct consequence of Liouville's theorem in the presence of a local turbulent magnetic field. We show that the predictions of this model are in excellent agreement with the observed power spectrum of multi-TeV CRs.PACS numbers: 98.70. Sa, 98.35.Eg Introduction.-The arrival directions of Galactic cosmic rays (CRs) are highly isotropic. This is expected from a diffusive propagation of CRs in the interstellar medium, where the effective scattering in turbulent magnetic fields randomizes the particle momenta over time. Diffusion theory (including also convective and dissipative processes) provides an excellent description of Galactic CR fluxes and their chemical abundances, e.g. [1]. In this framework the only deviation from an isotropic CR arrival direction is in the form of a weak dipole anisotropy. The phase and strength of this dipole is expected to be a combined effect of the relative motion of the solar system with respect to the frame where CRs are isotropic [2] and the density gradient of CRs in the direction of their sources [3][4][5].Cosmic ray anisotropies up to the level of one-per-mille have been observed at various energies by the observatories Tibet AS-γ [6,7] [17]. The explanation of the strength and phase of the observed dipole anisotropy is challenging, but is qualitatively consistent with the diffusive prediction [4]. However, some of the observations also show significant multi-TeV CR excesses at smaller angular scales with unknown origin. In particular, a high statistics sample of multi-TeV CRs seen by the IceCube observatory [16] shows significant power in small-scale multipole moments with 20 as shown in Fig. 1. It has been speculated that localized CR excesses can be a combined effect of CR acceleration in nearby supernova remnants [18] and the local intergalactic magnetic field structure introducing an energy-dependent magnetic mirror leakage [19] or preferred CR transport directions [20]. Magnetic reconnections in the heliotail [21], non-isotropic particle transport in the heliosheath [22] or the heliospheric electric field structure [23] have also been considered as a source of these small-scale anisotropies. Another variant considers the effect of magnetized outflow from old supernova remnants [24]. More exotic models invoke strangelet production in molecular clouds [25] or in neutron stars [26].

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The Large-Scale Cosmic-Ray Anisotropy as Observed With Milagro

Cited by 187 publications

References 20 publications

First year results from the HAWC observatory

First year results from the HAWC observatory

SEARCHES FOR LARGE-SCALE ANISOTROPY IN THE ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE ENERGY OF 10¹⁹eV AT THE PIERRE AUGER OBSERVATORY AND THE TELESCOPE ARRAY

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields

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The Large-Scale Cosmic-Ray Anisotropy as Observed With Milagro

Cited by 187 publications

References 20 publications

First year results from the HAWC observatory

First year results from the HAWC observatory

SEARCHES FOR LARGE-SCALE ANISOTROPY IN THE ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE ENERGY OF 1019eV AT THE PIERRE AUGER OBSERVATORY AND THE TELESCOPE ARRAY

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields

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SEARCHES FOR LARGE-SCALE ANISOTROPY IN THE ARRIVAL DIRECTIONS OF COSMIC RAYS DETECTED ABOVE ENERGY OF 10¹⁹eV AT THE PIERRE AUGER OBSERVATORY AND THE TELESCOPE ARRAY