Diffuse X-Ray Emission in the Cygnus OB2 Association

Albacete-Colombo, J. F.; Drake, J. J.; Flaccomio, E.; Wright, N. J.; Kashyap, V.; Guarcello, M. G.; Briggs, K.; Drew, J. E.; Fenech, D. M.; Micela, G.; McCollough, M.; Prinja, R. K.; Schneider, N.; Sciortino, S.; Vink, J. S.

doi:10.3847/1538-4365/acdd65

Cited by 4 publications

(1 citation statement)

References 59 publications

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“…Objects classified as members show a clear concentration that corresponds to the association, while the distribution of foreground objects is more isotropic. Objects classified as background show a small enhancement over regions of small A v (see also Albacete-Colombo et al 2023).…”

Section: Catalogmentioning

confidence: 99%

Classification of Chandra X-Ray Sources in Cygnus OB2

Kashyap,

Guarcello,

Wright

et al. 2023

ApJS

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We have devised a predominantly Naive Bayes−based method to classify X-ray sources detected by Chandra in the Cygnus OB2 association into members, foreground objects, and background objects. We employ a variety of X-ray, optical, and infrared characteristics to construct likelihoods using training sets defined by well-measured sources. Combinations of optical photometry from the Sloan Digital Sky Survey (riz) and Isaac Newton Telescope Photometric Hα Survey (r I i I Hα), infrared magnitudes from United Kingdom Infrared Telescope Deep Sky Survey and Two-Micron All Sky Survey (JHK), X-ray quantiles and hardness ratios, and estimates of extinction A v are used to compute the relative probabilities that a given source belongs to one of the classes. Principal component analysis is used to isolate the best axes for separating the classes for the photometric data, and Gaussian component separation is used for X-ray hardness and extinction. Errors in the measurements are accounted for by modeling as Gaussians and integrating over likelihoods approximated as quartic polynomials. We evaluate the accuracy of the classification by inspection and reclassify a number of sources based on infrared magnitudes, the presence of disks, and spectral hardness induced by flaring. We also consider systematic errors due to extinction. Of the 7924 X-ray detections, 5501 have a total of 5597 optical/infrared matches, including 78 with multiple counterparts. We find that ≈6100 objects are likely association members, ≈1400 are background objects, and ≈500 are foreground objects, with an accuracy of 96%, 93%, and 80%, respectively, with an overall classification accuracy of approximately 95%.

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Section: Catalogmentioning

confidence: 99%

Classification of Chandra X-Ray Sources in Cygnus OB2

Kashyap,

Guarcello,

Wright

et al. 2023

ApJS

Self Cite

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Cygnus OB2 as a test case for particle acceleration in young massive star clusters

Menchiari,

Morlino,

Amato

et al. 2024

A&A

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In this paper, we focus on the scientific case of Cygnus OB2, a young massive star cluster (YMSC) located in the northern sky towards the Cygnus X star-forming complex. We consider a model that assumes cosmic-ray acceleration occurring only at the termination shock of the collective wind of the YMSC and address the question of whether or not, and under what hypotheses, hadronic emission by the accelerated particles can account for the observations of Cygnus OB2 obtained by Fermi-LAT, HAWC, and LHAASO. To this end, we carefully review the available information on this source, also confronting different estimates of the relevant parameters with ad hoc developed simulations. Once other model parameters are fixed, the spectral and spatial properties of the emission are found to be very sensitive to the unknown properties of the turbulent magnetic field. Comparison with the data shows that our suggested scenario is incompatible with Kolmogorov turbulence. Assuming Kraichnan- or Bohm-type turbulence spectra, the model accounts well for the very high energy (VHE) data, but fails to reproduce the centrally peaked morphology observed by Fermi-LAT, suggesting that additional effects might be important for lower energy gamma -ray emission. We discuss how additional progress can be made with more detailed and extended knowledge of the spectral and morphological properties of the emission.

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Hydrodynamic simulation of Cygnus OB2: the absence of a cluster wind termination shock

Vieu,

Larkin,

Härer

et al. 2024

Monthly Notices of the Royal Astronomical Society

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We perform a large-scale hydrodynamic simulation of a massive star cluster whose stellar population mimics that of the Cygnus OB2 association. The main-sequence stars are first simulated during 1.6 Myr, until a quasi-stationary state is reached. At this time the three Wolf-Rayet stars observed in Cygnus OB2 are added to the simulation, which continues to 2 Myr. Using a high-resolution grid in the centre of the domain, we can resolve the most massive stars individually, which allows us to probe the kinetic structures at small (parsec) scales. We find that, although the cluster excavates a spherical ‘superbubble’ cavity, the stellar population is too loosely distributed to blow a large-scale cluster wind termination shock, and that collective effects from wind-wind interactions are much less efficient than usually assumed. This challenges our understanding of the ultra-high energy emission observed from the region.

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Diffuse X-Ray Emission in the Cygnus OB2 Association

Cited by 4 publications

References 59 publications

Classification of Chandra X-Ray Sources in Cygnus OB2

Classification of Chandra X-Ray Sources in Cygnus OB2

Cygnus OB2 as a test case for particle acceleration in young massive star clusters

Hydrodynamic simulation of Cygnus OB2: the absence of a cluster wind termination shock

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