The environment of the wind–wind collision region of <i>η</i> Carinae

Panagiotou, Christos; Walter, R.

doi:10.1051/0004-6361/201731841

Cited by 8 publications

(4 citation statements)

References 24 publications

(41 reference statements)

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“…This kind of activity occurs mainly during the Wolf-Rayet (WR) and Luminous Blue Variable (LBV) stages. It has been observed that in binary systems such winds collide producing very energetic signatures such as particle acceleration, X-ray and γ-ray emission (Abdo et al 2010;Hamaguchi et al 2016Hamaguchi et al , 2018Panagiotou & Walter 2018). In this case the material E-mail:dcaldero@astro.puc.cl launched at supersonic speeds on opposite directions collides generating dense shells of compressed shocked material at temperatures typically in the range ∼ 10 6 -10 7 K. However, binaries are not the only environments where stellar winds interact leaving energetic observational signatures.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional simulations of clump formation in stellar wind collisions

Calderón

Cuadra

Schartmann

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The inner parsec of our Galaxy contains tens of Wolf-Rayet stars whose powerful outflows are constantly interacting while filling the region with hot, diffuse plasma. Theoretical models have shown that, in some cases, the collision of stellar winds can generate cold, dense material in the form of clumps. However, their formation process and properties are not well-understood yet. In this work we present, for the first time, a statistical study of the clump formation process in unstable wind collisions. We study systems with dense outflows (Ṁ ∼ 10 −5 M yr −1 ), wind speeds of ∼ 500-1500 km s −1 , and stellar separations of ∼ 20-200 au. We develop 3D high resolution hydrodynamical simulations of stellar wind collisions, making use of the adaptive-mesh refinement grid-based code Ramses. We aim to characterise the initial properties of clumps that form through hydrodynamic instabilities, mostly via the non-linear thin shell instability. Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes, as long as such collisions are capable of creating cold, thin shells. Also, we find that increasing either the wind speed or the degree of asymmetry in the wind interaction increases the dispersion of the clump masses and ejection speed distribution. Nevertheless, our findings show that the most massive clumps are very light (∼ 10 −3 -10 −2 M ⊕ ), approximately three orders of magnitude less massive than theoretical upper limits. We apply our results to the central parsec of our Galaxy finding that clumps formed are not heavy enough neither to affect the thermodynamic state of the region nor to survive for long enough in order to fall onto the central super-massive black hole before being destroyed.

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Section: Introductionmentioning

confidence: 99%

Three-dimensional simulations of clump formation in stellar wind collisions

Calderón

Cuadra

Schartmann

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…The CWB was also detected up to giga-electronvolt energies with the AGILE and Fermi telescopes (Tavani et al 2009;Abdo et al 2010). However, detection of the hard X-ray emission between 10 keV and 20 keV with NuSTAR is somewhat uncertain (Hamaguchi et al 2018;Panagiotou & Walter 2018).…”

Section: Introductionmentioning

confidence: 99%

Search for non-thermal X-ray emission in the colliding wind binary Cygnus OB2 #8A

Mossoux

Pittard

Rauw

et al. 2020

A&A

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Aims. Cyg OB2 #8A is a massive O-type binary displaying strong non-thermal radio emission. Owing to the compactness of this binary, emission of non-thermal X-ray photons via inverse Compton scattering is expected. Methods. We first revised the orbital solution for Cyg OB2 #8A using new optical spectra. We then reduced and analysed X-ray spectra obtained with XMM-Newton, Swift, INTEGRAL, and NuSTAR.Results. The analysis of the XMM-Newton and Swift data allows us to better characterise the X-ray emission from the stellar winds and colliding winds region at energies below 10 keV. We confirm the variation of the broad-band light curve of Cyg OB2 #8A along the orbit with, for the first time, the observation of the maximum emission around phase 0.8. The minimum ratio of the X-ray to bolometric flux of Cyg OB2 #8A remains well above the level expected for single O-type stars, indicating that the colliding wind region is not disrupted during the periastron passage. The analysis of the full set of publicly available INTEGRAL observations allows us to refine the upper limit on the non-thermal X-ray flux of the Cyg OB2 region between 20 and 200 keV. Two NuSTAR observations (phases 0.028 and 0.085) allow us to study the Cyg OB2 #8A spectrum up to 30 keV. These data do not provide evidence of the presence of non-thermal X-rays, but bring more stringent constraints on the flux of a putative non-thermal component. Finally, we computed, thanks to a new dedicated model, the anisotropic inverse Compton emission generated in the wind shock region. The theoretical non-thermal emission appears to be compatible with observational limits and the kinetic luminosity computed from these models is in good agreement with the unabsorbed flux observed below 10 keV.

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“…Spectral energy distribution of η Carinae from 1 keV to 100 TeV. The data are from NuStar (Panagiotou & Walter ), Swift/BAT, INTEGRAL, Fermi LAT, and H.E.S.S, and obtained close to periastron. The red points show the results of a simulation of what could be detected by Cherenkov Telescope Array (CTA) (at periastron) assuming that the emission is dominated by π 0 decay modified by photo‐photo absorption in the strong ultraviolet photon field…”

Section: Introductionmentioning

confidence: 99%

η Carinae: Particle acceleration and multimessenger aspects

Walter

Balbo

2019

Astron Nachr

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Carinae is composed of two very massive stars orbiting each other in 5.5 years. The primary star features the densest known stellar wind, colliding with that expelled by its companion. The wind collision region dissipates energy and accelerates particles up to relativistic energies, producing nonthermal X-ray and -ray emission detected by Beppo-SAX, INTEGRAL, Swift, Suzaku, Agile, Fermi, and H.E.S.S. The orbital variability of the system provides key diagnosis of the physics involved and of the emission mechanisms. The low-energy component, which cuts off below 10 GeV and varies by a factor <2 along the orbit, is likely of the inverse Compton origin. The high-energy component varies by larger factors and differently during the two periastrons observed by Fermi. These variations match the predictions of simulations assuming a magnetic field in the range 0.4-1 kG at the surface of the primary star. The high-energy component and the thermal X-ray emission were weaker than expected around the 2014 periastron suggesting a modification of the inner wind density. Diffuse shock acceleration in the complex geometry of the wind collision zone provides a convincing match to the observations and new diagnostic tools to probe the geometry and energetics of the system. A future instrument sensitive in the MeV energy range could discriminate between lepto-hadronic and hadronic models for the gamma-ray emission. At higher energies, the Cherenkov Telescope Array will distinguish orbital modulations of the high-energy component from those of ultraviolet-TeV photoabsorption providing a wealth of information constraining acceleration physics under more extreme conditions than found in supernova remnants (SNR).

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The environment of the wind–wind collision region of η Carinae

Cited by 8 publications

References 24 publications

Three-dimensional simulations of clump formation in stellar wind collisions

Three-dimensional simulations of clump formation in stellar wind collisions

Search for non-thermal X-ray emission in the colliding wind binary Cygnus OB2 #8A

η Carinae: Particle acceleration and multimessenger aspects

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