Runaway O-star Bow Shocks as Particle Accelerators? The Case of AE Aur Revisited

Rangelov, Blagoy; Montmerle, T.; Federman, S. R.; Boissé, Patrick; Gabici, S.

doi:10.3847/1538-4357/ab43e5

Cited by 6 publications

(5 citation statements)

References 56 publications

(72 reference statements)

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“…Analytic models for the CR spectrum repower by the stellar terminal shocks are available (e.g., Webb et al 1985), showing a relatively high, typically 40% efficiency of the wind energy conversion into the reaccelerated CRs. Observations also indicate that powerful stellar winds accelerate particles efficiently (Rangelov et al 2019).…”

Section: Discussionmentioning

confidence: 99%

On the Origin of Observed Cosmic-Ray Spectrum Below 100 TV

Malkov

Moskalenko²

2022

ApJ

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Recent precise measurements of primary and secondary cosmic-ray (CR) species in the teravolt rigidity domain have unveiled a bump in their spectra, located between 0.5 and 50 TV. We argue that a local shock may generate such a bump by increasing the rigidity of the preexisting CRs below 50 TV by a mere factor of ∼1.5. Reaccelerated particles below ∼0.5 TV are convected with the interstellar medium flow and do not reach the Sun, thus creating the bump. This single universal process is responsible for the observed spectra of all CR species in the rigidity range below 100 TV. We propose that one viable shock candidate is the Epsilon Eridani star at 3.2 pc from the Sun, which is well aligned with the direction of the local magnetic field. Other shocks, such as old supernova shells, may produce a similar effect. We provide a simple formula, Equation (9), that reproduces the spectra of all CR species with only two nonadjustable shock parameters, uniquely derived from the proton data. We show how our formalism predicts helium and carbon spectra and the B/C ratio.

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Section: Discussionmentioning

confidence: 99%

On the Origin of Observed Cosmic-Ray Spectrum Below 100 TV

Malkov

Moskalenko²

2022

ApJ

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“…Especially its point source nature, without any hints for even faint extended emission surrounding it, argues for a coincident interloper. In addition, VLA radio studies at higher radio frequencies also did not detect any radio emission at the position of the bow shock, down to sensitivities below the flux density of the RACS source (Rangelov et al 2019). Based on the stellar wind properties and distance of HIP 24575 as listed in Peri et al (2015), we can use the formalism in Wright & Barlow (1975) to estimate the stellar wind's radio luminosity.…”

Section: Sourcementioning

confidence: 97%

Radio detections of IR-selected runaway stellar bow shocks

Eijnden

Saikia²,

Mohamed

2022

Monthly Notices of the Royal Astronomical Society

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Massive stars moving at supersonic peculiar velocities through the interstellar medium (ISM) can create bow shocks, arc-like structures at the interface between the stellar wind and the ISM. Many such bow shocks have been detected and catalogued at IR wavelengths, but detections in other wavebands remain rare. Strikingly, while electrons are expected to be accelerated in the bow shock and their non-thermal emission may include synchrotron emission at low frequencies, only two massive runaway stellar bow shocks have to date been detected in the radio band. Here, we examine a sample of fifty IR-detected bow shocks from the E-BOSS catalogues in recently released radio images from the Rapid ASKAP Continuum Survey (RACS). We identify three confident and three likely counterparts, as well as three inconclusive candidates requiring confirmation via follow-up observations. These detections significantly increase the number of known radio massive stellar bow shocks and highlight the advantage of dedicated searches with current and next-generation radio telescopes. We investigate the underlying radio emission mechanism for these radio sources, finding a mix of free-free-dominated and synchrotron-dominated systems. We also discuss the non-detected targets by putting constraints on their emission properties and investigating their detectability with future observations. Finally, we propose several future avenues of research to advance the study and understanding of bow shocks at radio frequencies.

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“…That said, DSA gives a proper framework in which particles can interact with the magnetic inhomogeneities in a way that could only increase the particles' energy (Bell 1978;Drury 1983;Blandford & Eichler 1987;Malkov & Drury 2001). Due to its efficiency, DSA has been used to describe the particle acceleration process in various astrophysical systems, for example in interplanetary heliospheric shocks (Jokipii et al 2007;Perri & Zimbardo 2015), shock waves of supernova remnants (Bell 2014), stellar bow shocks (Rangelov et al 2019), oblique shocks in AGN jets (Meli & Biermann 2013), and radio relics of galaxy clusters (Kang et al 2017;van Weeren et al 2017;Zimbardo & Perri 2017). Though DSA is more efficient compared to the STA mechanism, it is believed to only give rise to localized emission, where STA is thought to produce large-scale diffusive emission (Fan et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Numerical Modeling and Physical Interplay of Stochastic Turbulent Acceleration for Nonthermal Emission Processes

Kundu¹,

Vaidya²,

Mignone

2021

ApJ

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Particle acceleration is a ubiquitous phenomenon in astrophysical and space plasma. Diffusive shock acceleration (DSA) and stochastic turbulent acceleration (STA) are known to be the possible mechanisms for producing very highly energetic particles, particularly in weakly magnetized regions. An interplay of different acceleration processes along with various radiation losses is typically observed in astrophysical sources. While DSA is a systematic acceleration process that energizes particles in the vicinity of shocks, STA is a random energizing process, where the interaction between cosmic ray particles and electromagnetic fluctuations results in particle acceleration. This process is usually interpreted as a biased random walk in energy space, modeled through a Fokker-Planck equation. In the present work, we describe a novel Eulerian algorithm, adopted to incorporate turbulent acceleration in the presence of DSA and radiative processes like synchrotron and inverse Compton emission. The developed framework extends the hybrid Eulerian−Lagrangian module in a full-fledged relativistic Magneto-hydrodynamic (RMHD) code PLUTO. From our validation tests and case studies, we showcase the competing and complementary nature of both acceleration processes. Axisymmetric simulations of an RMHD jet with this extended hybrid framework clearly demonstrate that emission due to shocks is localized, while that due to turbulent acceleration originates in the backflow and is more diffuse, particularly in the high-energy X-ray band.

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Runaway O-star Bow Shocks as Particle Accelerators? The Case of AE Aur Revisited

Cited by 6 publications

References 56 publications

On the Origin of Observed Cosmic-Ray Spectrum Below 100 TV

On the Origin of Observed Cosmic-Ray Spectrum Below 100 TV

Radio detections of IR-selected runaway stellar bow shocks

Numerical Modeling and Physical Interplay of Stochastic Turbulent Acceleration for Nonthermal Emission Processes

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