University of Hertfordshire

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Diffuse X-ray emission in the Cygnus OB2 association

Research output: Contribution to journalArticle


  • 1806.01231

    Accepted author manuscript, 1 MB, PDF-document


  • J. F. Albacete Colombo
  • J. J. Drake
  • E. Flaccomio
  • N. J. Wright
  • V. Kashyap
  • M. G. Guarcello
  • K. Briggs
  • J. E. Drew
  • D. M. Fenech
  • G. Micela
  • M. McCollough
  • R. K. Prinja
  • N. Schneider
  • S. Sciortino
  • J. S. Vink
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Original languageEnglish
JournalAstrophysical Journal, Supplement Series
Journal publication dateJun 2018
Early online dateJun 2018
Publication statusE-pub ahead of print - Jun 2018


We present a large-scale study of diffuse X-ray emission in the nearby massive stellar association Cygnus OB2 as part of the Chandra Cygnus OB2 Legacy Program. We used 40 Chandra X-ray ACIS-I observations covering $\sim$1.0 deg$^2$. After removing 7924 point-like sources detected in our survey, background-corrected X-ray emission, the adaptive smoothing reveals large-scale diffuse X-ray emission. Diffuse emission was detected in the sub-bands Soft [0.5 : 1.2] and Medium [1.2 : 2.5], and marginally in the Hard [2.5 : 7.0] keV band. From X-ray spectral analysis of stacked spectra we compute a total [0.5 : 7.0 keV] diffuse X-ray luminosity of L$_{\rm x}^{\rm diff}\approx$4.2$\times$10$^{\rm 34}$ erg s$^{-1}$, characterized with plasma temperature components at kT$\approx$ 0.11, 0.40 and 1.18 keV, respectively. The HI absorption column density corresponding to these temperatures has a distribution consistent with N$_{\rm H}$ = 0.43, 0.80 and 1.39 $\times$10$^{22}$ cm$^{-2}$. The extended medium band energy emission likely arises from O-type stellar winds thermalized by wind-wind collisions in the most populated regions of the association, while the soft band emission probably arises from less energetic termination shocks against the surrounding Interstellar-Medium. Super-soft and Soft diffuse emission appears more widely dispersed and intense than the medium band emission. The diffuse X-ray emission is generally spatially coincident with low-extinction regions that we attribute to the ubiquitous influence of powerful stellar winds from massive stars and their interaction with the local Interstellar-Medium. Diffuse X-ray emission is volume-filling, rather than edge-brightened, oppositely to other star-forming regions. We reveal the first observational evidence of X-ray haloes around some evolved massive stars.


Accepted for publication on ApJSS, Cygnus OB2 Special Issue (2018). 20 pages, 19 figures


ID: 15142394