Anisotropic cosmic ray diffusion and its implications for gamma-ray astronomy

Giacinti, Gwenael; Kachelrieß, M.; Semikoz, D.

doi:10.1103/physrevd.88.023010

Cited by 27 publications

(34 citation statements)

References 81 publications

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“…On short scales, high energy CR particles are rather traveling along magnetic flux tubes as bulk movement (e.g., Giacinti et al 2013) with corresponding decoherence lengths of ∼100 pc. In the most extreme case, a monoenergetic particle distribution injected near the SNR could be preserved until the CRs hit a nearby molecular cloud.…”

Section: On the Isotropic Diffusion Assumptionmentioning

confidence: 99%

“…MC-J1729 can dominate the TeV emission outside the SNR assuming isotropic diffusion by adopting a reasonable three-dimensional molecular cloud structure. There is no need to invoke anisotropic CR diffusion (Jokipii 1966;Nava & Gabici 2013;Malkov et al 2013;Giacinti et al 2013) to boost the CR density in a particular direction.…”

Section: On the Isotropic Diffusion Assumptionmentioning

confidence: 99%

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A young supernova remnant illuminating nearby molecular clouds with cosmic rays

Cui

Pühlhofer

Santangelo

2016

A&A

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The supernova remnant (SNR) HESS J1731-347 displays strong nonthermal TeV γ-ray and X-ray emission, thus the object is presently accelerating particles to very high energies. A distinctive feature of this young SNR is the nearby (∼30 pc in projection) extended source HESS J1729-345, which is currently unidentified but is in spatial projection coinciding with known molecular clouds (MC). We model the SNR evolution to explore whether the TeV emission from HESS J1729-345 can be explained as emission from runaway hadronic cosmic rays (CRs) that are illuminating these MCs. The observational data of HESS J1729-345 and HESS J1731-347 can be reproduced using core-collapse SN models for HESS J1731-347. Starting with different progenitor stars and their presupernova environment, we model potential SNR evolution histories along with the CR acceleration in the SNR and the diffusion of the CRs. A simplified three-dimensional structure of the MCs is introduced based on 12 CO data of that region, adopting a distance of 3.2 kpc to the source. A Monte Carlo based diffusion model for the escaping CRs is developed to deal with the inhomogeneous environment. The fast SNR forward shock speed, as implied from the X-ray data, can easily be explained when employing scenarios with progenitor star masses between 20 M and 25 M , where the SNR shock is still expanding inside the main-sequence (MS) bubble at present time. The TeV spectrum of HESS J1729-345 is satisfactorily fitted by the emission from the highest energy CRs that have escaped the SNR, using a standard Galactic CR diffusion coefficient in the interclump medium. The TeV image of HESS J1729-345 can be explained with a reasonable three-dimensional structure of MCs. The TeV emission from the SNR itself is dominated by leptonic emission in this model. We also explore scenarios where the shock is starting to encounter the dense MS progenitor wind bubble shell. The escaping hadronic CR hypothesis for the γ-ray emission of HESS J1729-345 can still hold, but even in this case our model cannot easily account for the TeV emission from HESS J1731-347 in a hadronic scenario.

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Section: On the Isotropic Diffusion Assumptionmentioning

confidence: 99%

Section: On the Isotropic Diffusion Assumptionmentioning

confidence: 99%

A young supernova remnant illuminating nearby molecular clouds with cosmic rays

Cui

Pühlhofer

Santangelo

2016

A&A

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“…The jets would then be a visualisation of the ISM magnetic field in the surroundings of IGR J11014-6103 (compare the ISM magnetic field lines in e.g. Giacinti et al 2013; see also the discussions on the Double Helix Nebula, Morris et al 2006;Torii et al 2014). There is no obvious reason for which the underlying ISM structure would be comprised of similar conical helices converging towards the pulsar location; however, we note that the motion of the pulsar in the ISM could affect the distribution of the surrounding ISM material together with its magnetic field, for example through magnetic draping effects (e.g.…”

Section: Main Jetmentioning

confidence: 99%

Closer view of the IGR J11014-6103 outflows

Pavan

Pühlhofer

Bordas

et al. 2016

A&A

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IGR J11014-6103 (also known as the Lighthouse Nebula) is composed of a bow-shock pulsar wind nebula (PWN) and large-scale X-ray jet-like features, all powered by PSR J1101-6101. Previous observations suggest that the jet features stem from a ballistic jet of relativistic particles. In order to confirm the nature of the jet and the counter-jet, we obtained a new deep 250 ks Chandra observation of the Lighthouse Nebula. We performed detailed spatial and spectral analysis of all X-ray components of the system. The X-ray PWN is now better resolved and shows a peculiar morphology resembling the shape of an arrow. The overall helical pattern of the main jet is confirmed. However, there are large deviations from a simple helical model at small and large scales. Significant extended emission is now detected, encompassing the main jet all along its length. The presence of an apparent gap along the main jet at ∼50 distance from the pulsar is confirmed; however, the surrounding extended emission prevents conclusions on the coherence at this position of the jet. The counter-jet is now detected at high statistical significance. In addition, we found two small-scale arcs departing from the pulsar towards the jets. We also looked for possible bow-shock emission due to the pulsar motion, with a short VLT/FORS2 H-α observation. No clear emission is found, most likely because of the contamination from a diffuse nebulosity. The results of our X-ray analysis show that both a ballistic jet scenario and an alternative scenario involving the diffusion of particles along pre-existing interstellar magnetic field lines are able to satisfactorily explain some of the observational evidence, but cannot fully reproduce the observations.

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“…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.…”

mentioning

confidence: 59%

“…Therefore, CR distributions around recent sources should look anisotropic and irregular. This has important implications for γ-ray astronomy, and some first observations may hint at our findings, see [3]. Detailed comparisons at high and low photon energies of the extended γ-ray emissions around CR sources may give insights into the potential impact at low energies of CR-driven instabilities on the surrounding ISM.…”

Section: Discussionmentioning

confidence: 99%

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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Anisotropic cosmic ray diffusion and its implications for gamma-ray astronomy

Cited by 27 publications

References 81 publications

A young supernova remnant illuminating nearby molecular clouds with cosmic rays

A young supernova remnant illuminating nearby molecular clouds with cosmic rays

Closer view of the IGR J11014-6103 outflows

Cosmic ray propagation in the interstellar magnetic fields

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