Embedded star clusters as sources of high-energy cosmic rays: Modelling and constraints

Abstract

Massive stars are mainly found in stellar associations. These massive star clusters occur in the heart of giant molecular clouds. The strong stellar wind activity in these objects generates large bubbles and induces collective effects that could accelerate particles up to high energy and produce gamma rays. The best way to input an acceleration origin to the stellar wind interaction in massive stellar cluster is to observe young massive star clusters in which no supernova explosion has occurred yet. This work aims to constrain the part of stellar wind mechanical energy that is converted into energetic particles using the sensitivity of the ongoing Fermi/LAT instrument. This work further provides detailed predictions of expected gamma-ray fluxes in the view of the on-set of the next generation of imaging atmospheric Cherenkov telescopes. A one-zone model where energetic particles are accelerated by repeated interactions with strong supersonic shocks occurring in massive star clusters was developed. The particle escape from the star cluster and subsequent interaction with the surrounding dense material and magnetic fields of the HII region was computed. We applied this model to a selection of eight embedded star clusters constricted by existing observations. We evaluated the gamma-ray signal from each object, combining both leptonic and hadronic contributions. We searched for these emissions in the Fermi/LAT observations in the energy range from 3 to 300 GeV and compared them to the sensitivity of the Cherenkov Telescope Array. No significant gamma-ray emission from these star clusters has been found. Less than 10% of stellar wind luminosities are supplied to the relativistic particles. Some clusters even show acceleration efficiency of less than 1%. The CTA would be able to detect gamma-ray emission from several clusters in the case of an acceleration efficiency of close to 1%.

accepted for publication in Astronomy&Astrophysics

References in corpus (7)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Observational constraints on energetic particle diffusion in young SNRs: amplified magnetic field and maximum energy
• The exceptionally powerful TeV gamma-ray emitters in the Large Magellanic Cloud
• The young stellar population in M17 revealed by Chandra
• The first full orbit of Eta Carinae seen by Fermi
• MARCOS, a numerical tool for the simulation of multiple time-dependent non-linear diffusive shock acceleration
• The XMM-Newton X-ray Spectra of the Most X-ray Luminous Radio-quiet ROSAT Bright Survey-QSOs: A Reference Sample for the Interpretation of High-redshift QSO Spectra

Cited by in corpus (12)

• Science with e-ASTROGAM (A space mission for MeV-GeV gamma-ray astrophysics)
• Search for Spatial Extension in High-Latitude Sources Detected by the Fermi Large Area Telescope
• High-energy particles and radiation in star-forming regions
• Cosmic ray production in superbubbles
• Gamma rays as probes of cosmic-ray propagation and interactions in galaxies
• The contribution of winds of star clusters to the Galactic cosmic-ray population
• Constraining cosmic ray acceleration in young star clusters using multi-wavelength observations
• Extended Gamma-ray Emission from the G25.0+0.0 Region: A Star Forming Region Powered by the Newly Found OB Association?
• Sensitivity of the Cherenkov Telescope Array to TeV photon emission from the Large Magellanic Cloud
• Comparative study of gamma-ray emission from molecular clouds and star-forming galaxies
• Massive Star Clusters as sources of high-energy gamma radiation
• Exploring non-thermal emission from the star-forming region NGC 3603 through a realistic modelling of its environment