The puzzling MILAGRO hot spots

Drury, L. O’c.; Aharonian, F.

doi:10.1016/j.astropartphys.2008.04.007

Cited by 76 publications

(81 citation statements)

References 15 publications

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“…For this reason, the detection of SNRs in VHE gamma-rays was long awaited and considered a test for CR origin [3]. However, the detection of several SNRs in VHE gamma-rays cannot be considered a proof of CR acceleration because leptonic processes (most notably inverse Compton scattering) could as well explain the observed emission [4].…”

Section: Ricap-2014mentioning

confidence: 99%

“…(1) we implicitly assumed that the CR spectrum is ∝ E −2 and extends from E min = 1 GeV to E max = 4 PeV, which is the energy of the CR knee. This is a large flux, well within the reach of current Cherenkov telescopes, unless the SNR is too far away or the ambient density is much lower than the average one in the Galaxy [3]. A spectrum much steeper than E −2 and/or a cutoff in the spectrum at an energy much lower than that of the knee would result is a dramatic suppression of the VHE gamma-…”

Section: Introductionmentioning

confidence: 99%

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Gamma-ray emission from young supernova remnants: Hadronic or leptonic?

Gabici

Aharonian

2016

EPJ Web of Conferences

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Abstract. The debate on the nature of the gamma-ray emission from young supernova remnants is still open. Ascribing such emission to hadronic rather than leptonic processes would provide an evidence for the acceleration of protons and nuclei, and this fact would fit with the very popular (but not proven) paradigm that supernova remnants are the sources of Galactic cosmic rays. Here, we discuss this issue with a particular focus on the best studied gamma-ray-bright supernova remnant: RX J1713.7-3946.

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Section: Ricap-2014mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Gamma-ray emission from young supernova remnants: Hadronic or leptonic?

Gabici

Aharonian

2016

EPJ Web of Conferences

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“…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.…”

mentioning

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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“…Previous works have assumed additional effects so as to explain the SSA, see for example Refs. [17]. We demonstrate here that no additional effect is needed, and that rigidity-dependent SSA automatically arise from the local realization of the random magnetic field within about a CR MFP from Earth.…”

Section: Origin Of Tev-pev Cosmic Ray Anisotropiesmentioning

confidence: 94%

Cosmic ray propagation in the interstellar magnetic fields

Giacinti¹

2013

Plasma Phys. Control. Fusion

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Abstract. The propagation of TeV-PeV cosmic rays (CR) in our Galaxy can be described as a diffusive process. We discuss here two effects, with important observational consequences, that cannot be predicted by the diffusion approximation (DA) in its usual form. First, we present an explanation for the CR anisotropies observed at small angular scales on the sky. We show that the local magnetic field configuration within a CR mean free path from Earth naturally results in CR flux anisotropies at small and medium scales [1]. Second, we point out that TeVPeV CRs should be expected to diffuse strongly anisotropically in the interstellar medium on scales smaller than the maximum scale of spatial fluctuations of the field, ∼ 100 pc [2,3]. This notably questions the usual assumptions on CR diffusion around sources.

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The puzzling MILAGRO hot spots

Cited by 76 publications

References 15 publications

Gamma-ray emission from young supernova remnants: Hadronic or leptonic?

Gamma-ray emission from young supernova remnants: Hadronic or leptonic?

Anomalous Anisotropies of Cosmic Rays from Turbulent Magnetic Fields

Cosmic ray propagation in the interstellar magnetic fields

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