An X‐Ray Imaging Study of the Stellar Population in RCW 49

Tsujimoto, Masahiro; Feigelson, E. D.; Townsley, Leisa K.; Broos, P. S.; Getman, Konstantin V.; Wang, J.; Garmire, G. P.; Baba, Daisuke; Nagayama, Takahiro; Tamura, Motohide; Churchwell, E.

doi:10.1086/519681

Cited by 37 publications

(43 citation statements)

References 76 publications

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“…We assume that the giant HII region RCW49 of size 100 pc is the structure blown by Westerlund 2. Tsujimoto et al (2007) provided a spectral fit of the diffuse X-ray emission from RCW49, from which we deduce a density ∼1.5 × 10 −3 cm −3 . We note that Westerlund 2 was detected by HESS (Aharonian et al 2007).…”

Section: Galaxymentioning

confidence: 95%

On the shape of the spectrum of cosmic rays accelerated inside superbubbles

Ferrand¹,

Marcowith²

2010

A&A

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Context. Supernova remnants are believed to be a major source of energetic particles (cosmic rays) on the Galactic scale. Since their progenitors, namely the most massive stars, are commonly found clustered in OB associations, one has to consider the possibility of collective effects in the acceleration process. Aims. We investigate the shape of the spectrum of high-energy protons produced inside the superbubbles blown around clusters of massive stars. Methods. We embed simple semi-analytical models of particle acceleration and transport inside Monte Carlo simulations of OB associations timelines. We consider regular acceleration (Fermi 1 process) at the shock front of supernova remnants, as well as stochastic reacceleration (Fermi 2 process) and escape (controlled by magnetic turbulence) occurring between the shocks. In this first attempt, we limit ourselves to linear acceleration by strong shocks and neglect proton energy losses. Results. We observe that particle spectra, although highly variable, have a distinctive shape because of the competition between acceleration and escape: they are harder at the lowest energies (index s < 4) and softer at the highest energies (s > 4). The momentum at which this spectral break occurs depends on the various bubble parameters, but all their effects can be summarized by a single dimensionless parameter, which we evaluate for a selection of massive star regions in the Galaxy and the LMC. Conclusions. The behaviour of a superbubble in terms of particle acceleration critically depends on the magnetic turbulence: if B is low then the superbubble is simply the host of a collection of individual supernovae shocks, but if B is high enough (and the turbulence index is not too high), then the superbubble acts as a global accelerator, producing distinctive spectra, that are potentially very hard over a wide range of energies, which has important implications on the high-energy emission from these objects.

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Section: Galaxymentioning

confidence: 95%

On the shape of the spectrum of cosmic rays accelerated inside superbubbles

Ferrand¹,

Marcowith²

2010

A&A

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“…An X-ray source, CXOU J102302.8-574606.9 (Tsujimoto et al 2007), found in a 130 ks Chandra observation has been suggested as a potential counterpart, 8 apart from the Westerlund 2 core, and its relation to the stellar cluster thus remains unknown. A distance to CXOU J102302.8-574606.9 of >10 kpc was proposed based on the column density from Chandra observations (Dormody et al 2009).…”

Section: Hess J1023-575mentioning

confidence: 99%

Revisiting the Westerlund 2 field with the HESS telescope array

Abramowski¹,

Acero²,

Aharonian³

et al. 2010

A&A

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Aims. Previous observations with the HESS telescope array revealed the existence of extended very-high-energy (VHE; E > 100 GeV) γ-ray emission, HESS J1023-575, coincident with the young stellar cluster Westerlund 2. At the time of discovery, the origin of the observed emission was not unambiguously identified, and follow-up observations have been performed to further investigate the nature of this γ-ray source. Methods. The Carina region towards the open cluster Westerlund 2 has been re-observed, increasing the total exposure to 45.9 h. The combined dataset includes 33 h of new data and now permits a search for energy-dependent morphology and detailed spectroscopy. Results. A new, hard spectrum VHE γ-ray source, HESS J1026-582, was discovered with a statistical significance of 7σ. It is positionally coincident with the Fermi LAT pulsar PSR J1028-5819. The positional coincidence and radio/γ-ray characteristics of the LAT pulsar favors a scenario where the TeV emission originates from a pulsar wind nebula. The nature of HESS J1023-575 is discussed in light of the deep HESS observations and recent multi-wavelength discoveries, including the Fermi LAT pulsar PSR J1022-5746 and giant molecular clouds in the region. Despite the improved VHE dataset, a clear identification of the object responsible for the VHE emission from HESS J1023-575 is not yet possible, and contribution from the nearby high-energy pulsar and/or the open cluster remains a possibility.

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“…Very recently, Tsujimoto et al (2007) identified 468 X-ray sources in Wd2 with Chandra and fit each of the stronger 230 of these with an optically thin thermal plasma (APEC) model to derive foreground N(H). The sources are spread over a cluster core radius of -, a good 6 7 match to the resolution of the CO data used here.…”

Section: Distancementioning

confidence: 99%

On the Distance and Molecular Environment of Westerlund 2 and HESS J1023-575

Dame¹

2007

ApJ

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The extended TeV gamma-ray source HESS J1023Ϫ575 is coincident with the massive, young stellar cluster Westerlund 2 (Wd2) and its surrounding H ii region RCW 49. On the basis of an analysis of the CO emission and 21 cm absorption along the line of sight to Wd2, it is argued that this cluster, and by assumption the TeV source as well, must be associated with a giant molecular cloud in the far side of the Carina arm with a mass of . Analysis of the spatial and velocity structure of the cloud reveals clear evidence of interaction 5 7.5 # 10 M , with Wd2. The cloud's kinematic distance of kpc is shown to be consistent with distances inferred 6.0 ‫ע‬ 1.0 from both the radius-line width relation of molecular clouds and the foreground gas column derived from 230 X-ray sources in Wd2.

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An X‐Ray Imaging Study of the Stellar Population in RCW 49

Cited by 37 publications

References 76 publications

On the shape of the spectrum of cosmic rays accelerated inside superbubbles

On the shape of the spectrum of cosmic rays accelerated inside superbubbles

Revisiting the Westerlund 2 field with the HESS telescope array

On the Distance and Molecular Environment of Westerlund 2 and HESS J1023-575

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