Limiting the shock acceleration of cosmic ray protons in the ICM

Wittor, Denis; Vazza, Franco; Ryu, Dongsu; Kang, Hyesung

doi:10.1093/mnrasl/slaa066

Cited by 31 publications

(41 citation statements)

References 31 publications

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“…CRe are accelerated preferentially at quasi-perpendicular shocks and CRp at quasi-parallel shocks. Recent works by Wittor et al (2020) and Banfi, Vazza & Wittor (2020) used cosmological MHD simulations to show that indeed the predominance of quasi-perpendicular shocks in merger and accretion shocks might be enough to explain the absence of CRp. Therefore, in future work we will include the obliquity dependence in our acceleration efficiency, η.…”

Section: S U M M a Ry A N D C O N C L U S I O N Smentioning

confidence: 99%

Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Domínguez-Fernández

Brüggen

Vazza

et al. 2020

Monthly Notices of the Royal Astronomical Society

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High-resolution radio observations of cluster radio relics often show complex spatial and spectral features. However, it is not clear what these features reveal about the underlying magnetic field properties. We performed three-dimensional magneto-hydrodynamical simulations of merger shock waves propagating through a magnetised, turbulent intracluster medium. Our model includes the diffusive shock acceleration of cosmic-ray electrons, their spatial advection and energy losses at run-time. With this set-up we can investigate the relation between radio substructure and pre-shock plasma conditions in the host cluster. We find that upstream turbulence plays a major role in shaping the properties of radio relics produced downstream. Within the assumption of diffusive shock acceleration, we can reproduce the observed discrepancy between the X-ray derived Mach number of shocks, and the Mach number inferred from radio spectra. Our simulated spectral index maps and profiles across the radio relic also suggest that the standard deviation of the upstream magnetic field must be relatively small (σB ≤ 1 μG) in order to reproduce observations and therefore, radio relics can potentially constrain the distribution of magnetic fields in galaxy clusters outskirts.

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Section: S U M M a Ry A N D C O N C L U S I O N Smentioning

confidence: 99%

Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Domínguez-Fernández

Brüggen

Vazza

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Yet, only a direct detection of a γ-ray signal associated with cosmic-ray protons in the ICM will allow to pin-point the exact shock acceleration mechanism. Though, estimates by Wittor et al (2020) showed that, even after ten more years of operation, the Fermi-LAT will most-likely not detect such a signal, see Fig. 5.…”

Section: Will There Be a Detection In The Future?mentioning

confidence: 98%

“…During the processes of hierarchical structure formation, galaxy clusters form through 1 Here, β is the plasma β that gives the ratio between gas pressure and magnetic pressure. Wittor et al (2020): the two panels show the expected γ-ray emission (color) of two simulated galaxy clusters at redshift z = 0. The underlying cosmic-ray model is the most restricted one, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…Results given inWittor et al (2020): The plot compares the total γ-ray flux the simulated sample ofWittor et al (2020) with the upper limits given by the Fermi-LAT. Specifically, the grey crosses give the limites in the energy range [0.5, 200] GeV Ackermann et al (2014).…”

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confidence: 99%

“…The black crosses display the γ-ray flux obtained for the "old" acceleration efficiencies calculated byKang and Ryu (2013). (The plot has been modified from its original version to fit the style of this paper).In a complementary work,Wittor et al (2020) combined cosmological simulations and Lagrangian tracer particles to study the cosmic-ray proton acceleration in four massive galaxy clusters, i.e. 5.4 • 10 14 − 1.1 • 10 15 M (seeFig.…”

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confidence: 99%

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On the Challenges of Cosmic-Ray Proton Shock Acceleration in the Intracluster Medium

Wittor

2021

New Astronomy

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Galaxy clusters host the largest particle accelerators in the Universe: Shock waves in the intracluster medium (ICM), a hot and ionised plasma, that accelerate particles to high energies. Radio observations pick up synchrotron emission in the ICM, proving the existence of accelerated cosmic-ray electrons. However, a sign of cosmic-ray protons, in form of γ-rays. remains undetected. This is know as the missing γ-ray problem and it directly challenges the shock acceleration mechanism at work in the ICM. Over the last decade, theoretical and numerical studies focused on improving our knowledge on the microphysics that govern the shock acceleration process in the ICM. These new models are able to predict a γ-ray signal, produced by shock accelerated cosmic-ray protons, below the detection limits set modern γ-ray observatories. In this review, we summarise the latest advances in solving the missing γ-ray problem.

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Are Odd Radio Circles phoenixes of powerful radio galaxies?

Shabala,

Yates-Jones,

Jerrim

et al. 2024

Publ. Astron. Soc. Aust.

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Odd Radio Circles (ORCs) are a class of low surface brightness, circular objects approximately one arcminute in diameter. ORCs were recently discovered in the Australian Square Kilometre Array Pathfinder (ASKAP) data, and subsequently confirmed with follow-up observations on other instruments, yet their origins remain uncertain. In this paper, we suggest that ORCs could be remnant lobes of powerful radio galaxies, re-energised by the passage of a shock. Using relativistic hydrodynamic simulations with synchrotron emission calculated in post-processing, we show that buoyant evolution of remnant radio lobes is alone too slow to produce the observed ORC morphology. However, the passage of a shock can produce both filled and edge-brightnened ORC-like morphologies for a wide variety of shock and observing orientations. Circular ORCs are predicted to have host galaxies near the geometric centre of the radio emission, consistent with observations of these objects. Significantly offset hosts are possible for elliptical ORCs, potentially causing challenges for accurate host galaxy identification. Observed ORC number counts are broadly consistent with a paradigm in which moderately powerful radio galaxies are their progenitors.

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Limiting the shock acceleration of cosmic ray protons in the ICM

Cited by 31 publications

References 31 publications

Morphology of radio relics – I. What causes the substructure of synchrotron emission?

Morphology of radio relics – I. What causes the substructure of synchrotron emission?

On the Challenges of Cosmic-Ray Proton Shock Acceleration in the Intracluster Medium

Are Odd Radio Circles phoenixes of powerful radio galaxies?

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