Diffuse thermal X-ray emission in the core of the young massive cluster Westerlund 1

Kavanagh, Patrick; Norci, L.; Meurs, E. J. A.

doi:10.1016/j.newast.2011.04.001

Cited by 15 publications

(15 citation statements)

References 34 publications

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“…To address the dilemma Kavanagh et al (2011) analyzed a 48 ks XMM-Newton observation of Westerlund 1 and found He-like Fe 6.7 keV line emission in the central 2 region suggesting that the hard X-rays from the cluster core are mostly thermal in their origin. They concluded that the majority of the hard emission in the inner 2 annuli likely comes from the thermalized cluster wind (see also models by Oskinova 2005) with a contribution from the pre-main sequence stellar population, while it is unlikely that SNRs are contributing significantly to the diffuse emission of Westerlund 1 at the current epoch.…”

Section: Westerlund I Supercluster and The Magnetar Cxou J1647-45mentioning

confidence: 99%

“…They concluded that the majority of the hard emission in the inner 2 annuli likely comes from the thermalized cluster wind (see also models by Oskinova 2005) with a contribution from the pre-main sequence stellar population, while it is unlikely that SNRs are contributing significantly to the diffuse emission of Westerlund 1 at the current epoch. The Fe line signatures were not found in the outer extraction annuli by Kavanagh et al (2011) and therefore the question of the thermal or non-thermal origin of the hard emission in the outer regions has been left open.…”

Section: Westerlund I Supercluster and The Magnetar Cxou J1647-45mentioning

confidence: 99%

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Nonthermal particles and photons in starburst regions and superbubbles

Bykov

2014

Astron Astrophys Rev

118

102

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Starforming factories in galaxies produce compact clusters and loose associations of young massive stars. Fast radiation-driven winds and supernovae input their huge kinetic power into the interstellar medium in the form of highly supersonic and superalfvenic outflows. Apart from gas heating, collisionless relaxation of fast plasma outflows results in fluctuating magnetic fields and energetic particles. The energetic particles comprise a long-lived component which may contain a sizeable fraction of the kinetic energy released by the winds and supernova ejecta and thus modify the magnetohydrodynamic flows in the systems. We present a concise review of observational data and models of nonthermal emission from starburst galaxies, superbubbles, and compact clusters of massive stars. Efficient mechanisms of particle acceleration and amplification of fluctuating magnetic fields with a wide dynamical range in starburst regions are discussed. Sources of cosmic rays, neutrinos and multi-wavelength nonthermal emission associated with starburst regions including potential galactic "PeVatrons" are reviewed in the global galactic ecology context.

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Section: Westerlund I Supercluster and The Magnetar Cxou J1647-45mentioning

confidence: 99%

Section: Westerlund I Supercluster and The Magnetar Cxou J1647-45mentioning

confidence: 99%

Nonthermal particles and photons in starburst regions and superbubbles

Bykov

2014

Astron Astrophys Rev

118

102

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“…More recently, Kavanagh et al (2011) analyze an XMM-Newton pointing and determine that the hard component in an inner 2 arcmin radius region is actually thermal, with a clearly detected He-like Fe 6.4 keV line. No evidence of a non-thermal component was found.…”

Section: A7 Westerlundmentioning

confidence: 99%

Feedback from winds and supernovae in massive stellar clusters – II. X-ray emission

Rogers

Pittard

2014

Monthly Notices of the Royal Astronomical Society

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The X-ray emission from a simulated massive stellar cluster is investigated. The emission is calculated from a 3D hydrodynamical model which incorporates the mechanical feedback from the stellar winds of 3 O-stars embedded in a giant molecular cloud (GMC) clump containing 3240 M ⊙ of molecular material within a 4 pc radius. A simple prescription for the evolution of the stars is used, with the first supernova explosion at t = 4.4 Myrs. We find that the presence of the GMC clump causes shortlived attenuation effects on the X-ray emission of the cluster. However, once most of the material has been ablated away by the winds the remaining dense clumps do not have a noticable effect on the attenuation compared with the assumed interstellar medium (ISM) column. We determine the evolution of the cluster X-ray luminosity, L X , and spectra, and generate synthetic images. The intrinsic X-ray luminosity drops from nearly 10 34 ergs s −1 while the winds are 'bottled up', to a near constant value of 1.7×10 32 ergs s −1 between t = 1-4 Myrs. L X reduces slightly during each star's red supergiant (RSG) stage due to the depressurization of the hot gas. However, L X increases to ≈ 10 34 ergs s −1 during each star's Wolf-Rayet (WR) stage. The X-ray luminosity is enhanced by 2-3 orders of magnitude to ∼ 10 37 ergs s −1 for at least 4600 yrs after each supernova (SN) explosion, at which time the blast wave leaves the grid and the X-ray luminosity drops. The X-ray luminosity of our simulation is generally considerably fainter than predicted from spherically-symmetric bubble models, due to the leakage of hot gas material through gaps in the outer shell. This process reduces the pressure within our simulation and thus the X-ray emission. However, the X-ray luminosities and temperatures which we obtain are comparable to similarly powerful massive young clusters.

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“…The main alternative explanation for the ionized nebula around W26 is that it is hydrodynamically confined by the pressure of the intracluster gas. This could be ram pressure from stellar winds or a global cluster wind (Dougherty et al 2010), or thermal pressure from thermalised shocked wind bubble and recent supernovae that must have occurred in Westerlund 1 (Muno et al 2006;Kavanagh et al 2011). …”

Section: Introductionmentioning

confidence: 99%

Cold gas in hot star clusters: the wind from the red supergiant W26 in Westerlund 1

Mackey

Castro²,

Fossati

et al. 2015

A&A

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The massive red supergiant W26 in Westerlund 1 is one of a growing number of red supergiants shown to have winds that are ionized from the outside in. The fate of this dense wind material is important for models of second generation star formation in massive star clusters. Mackey et al. (2014, Nature, 512, 282) showed that external photoionization can stall the wind of red supergiants and accumulate mass in a dense static shell. We use spherically symmetric radiation-hydrodynamic simulations of an externally photoionized wind to predict the brightness distribution of Hα and [N II] emission arising from photoionized winds both with and without a dense shell. We analyse spectra of the Hα and [N II] emission lines in the circumstellar environment around W26 and compare them with simulations to investigate whether W26 has a wind that is confined by external photoionization. Simulations of slow winds that are decelerated into a dense shell show strongly limb-brightened line emission, with line radial velocities that are independent of the wind speed. Faster winds ( 22 km s −1 ) do not form a dense shell, have less limb-brightening, and the line radial velocity is a good tracer of the wind speed. The brightness of the [N II] and Hα lines as a function of distance from W26 agrees reasonably well with observations when only the line flux is considered. The radial velocity of the simulated winds disagrees with observations, however: the brightest observed emission is blueshifted by ≈25 km s −1 relative to the radial velocity of the star, whereas a spherically symmetric wind has the brightest emission at zero radial velocity because of limb brightening. Our results show that the bright nebula surrounding W26 must be asymmetric, and we suggest that it is confined by external ram pressure from the extreme wind of the nearby supergiant W9. We obtain a lower limit on the nitrogen abundance within the nebula of 2.35 times solar. The line ratio strongly favours photoionization over shock ionization, and so even if the observed nebula is pressure confined there should still be an ionization front and a photoionization-confined shell closer to the star that is not resolved by the current observations, which could be tested with better spectral resolution and spatial coverage.

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Diffuse thermal X-ray emission in the core of the young massive cluster Westerlund 1

Cited by 15 publications

References 34 publications

Nonthermal particles and photons in starburst regions and superbubbles

Nonthermal particles and photons in starburst regions and superbubbles

Feedback from winds and supernovae in massive stellar clusters – II. X-ray emission

Cold gas in hot star clusters: the wind from the red supergiant W26 in Westerlund 1

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