Gamma-rays, neutrinos and cosmic rays from dense regions in open clusters

Bednarek, W.; Pabich, J.; Sobczak, T.

doi:10.1016/j.nuclphysbps.2014.10.013

Cited by 5 publications

(2 citation statements)

References 35 publications

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“…Single massive stars, especially stars with dense winds, such as WRs, are also a potential source for generating cosmic rays, via shocks between the stellar winds and their circumstellar environments (Cesarsky & Montmerle 1983). The generation of cosmic rays in the stellar winds of massive stars are believed to be possible in the locations of open clusters in particular, where the regions of interstellar material and a possible strong radiation field can help to sustain cosmic rays produced by stellar sources, either via their winds or from the resultant SNe (Bednarek et al 2014).…”

Section: Introductionmentioning

confidence: 99%

A radio census of the massive stellar cluster Westerlund 1

Andrews

Fenech

Prinja

et al. 2019

A&A

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Context. Massive stars and their stellar winds are important for a number of feedback processes. The mass lost in the stellar wind can help determine the end-point of the star as a NS or a BH. However, the impact of mass-loss on the post-Main Sequence evolutionary stage of massive stars is not well understood. Westerlund 1 is an ideal astrophysical laboratory in which to study massive stars and their winds in great detail over a large range of different evolutionary phases. Aims. We aim to study the radio emission from Westerlund 1, in order to measure radio fluxes from the population of massive stars, and determine mass-loss rates and spectral indices where possible. Methods. Observations were carried out in 2015 and 2016 with the Australia telescope compact array (ATCA) at 5.5 and 9 GHz using multiple configurations, with maximum baselines ranging from 750 m to 6 km. Results. 30 stars were detected in the radio from the fully concatenated dataset, 10 of which were WRs (predominantly late type WN stars), 5 YHGs, 4 RSGs, 1 LBV star, the sgB[e] star W9, and several O and B supergiants. New source detections in the radio were found for 5 WR stars, and 5 OB supergiants. These detections have led to evidence for 3 new OB supergiant binary candidates, inferred from derived spectral index limits. Conclusions. Spectral indices and index limits were determined for massive stars in Westerlund 1. For cluster members found to have partially optically thick emission, mass-loss rates were calculated. Under the approximation of a thermally emitting stellar wind and a steady mass-loss rate, clumping ratios were then estimated for 8 WRs. Diffuse radio emission was detected throughout the cluster. Detections of knots of radio emission with no known stellar counterparts indicate the highly clumped structure of this intra-cluster medium, likely shaped by a dense cluster wind.

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Section: Introductionmentioning

confidence: 99%

A radio census of the massive stellar cluster Westerlund 1

Andrews

Fenech

Prinja

et al. 2019

A&A

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“…However, another immediate way of proceeding is represented by searching for different CR accelerators in order to supply the amount of CRs required to explain local CR density. Indeed, several other CR accelerators have been proposed, such as binary systems in open star clusters (e.g., [36]), protostellar jets (e.g., [37]), and novae (e.g., [38]), as well as extragalactic sources such as gamma ray bursts (e.g., [39]) and active galactic nuclei (e.g., [40]). The Galactic Center itself has been proposed (e.g., [41]), and has been proven to be an efficient CR accelerator [42].…”

Section: Possible (Obvious) Solutionsmentioning

confidence: 99%

Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources

Tibolla

Kaufmann

Chadwick

2022

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The riddle of the origin of Cosmic Rays (CR) has been an open question for over a century. Gamma ray observations above 100 MeV reveal the sites of cosmic ray acceleration to energies where they are unaffected by solar modulation; recent evidence supports the existence of hadronic acceleration in Supernova Remnants (SNR), as expected in the standard model of cosmic ray acceleration. Nevertheless, the results raise new questions, and no final answer has been provided thus far. Among the suggested possible alternative accelerators in the Very High Energy (VHE) gamma ray sky, pulsar wind nebulae (PWNe, which together with dark matter are the main candidates to explain the local positron excess as well) are the dominant population among known Galactic sources. However, the most numerous population in absolute terms is represented by unidentified sources (~50% of VHE gamma ray sources). The relationship between PWNe and unidentified sources seems very close; in fact, in a PWN, the lifetime of inverse Compton (IC) emitting electrons not only exceeds the lifetime of its progenitor pulsar, but also exceeds the age of the electrons that emit via synchrotron radiation. Therefore, during its evolution, a PWN can remain bright in IC such that its GeV-TeV gamma ray flux remains high for timescales much larger than the lifetimes of the pulsar and the X-ray PWN. In addition, the shell-type remnant of the supernova explosion in which the pulsar was formed has a much shorter lifetime than the electrons responsible for IC emission. Hence, understanding PWNe and VHE unidentified sources is a crucial piece of the solution to the riddle of the origin of cosmic rays. Both theoretical aspects (with particular emphasis on the ancient pulsar wind nebulae scenario) and their observational proofs are discussed in this paper. Specifically, the scientific cases of HESS J1616-508 and HESS J1813-126 are examined in detail.

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Prolegomena

Tibolla

Drury

2014

Nuclear Physics B - Proceedings Supplements

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Gamma-rays, neutrinos and cosmic rays from dense regions in open clusters

Cited by 5 publications

References 35 publications

A radio census of the massive stellar cluster Westerlund 1

A radio census of the massive stellar cluster Westerlund 1

Pulsar Wind Nebulae and Unidentified Galactic Very High Energy Sources

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