2003ApJ...597..494B

The High Energy Gamma Ray Astronomy (HEGRA) Cerenkov telescope array group recently reported a steady and extended unidentified TeV gamma-ray source lying at the outskirts of Cygnus OB2. This is the most massive stellar association known in the Galaxy, estimated to contain ∼2600 OB-type members alone. It has been previously argued that the large-scale shocks and turbulence induced by the multiple interacting supersonic winds from the many young stars in such associations may play a role in accelerating Galactic cosmic rays. Indeed, Cyg OB2 also coincides with the nonvariable MeV-GeV range unidentified EGRET source, 3EG 2033+4118. We report on the near-simultaneous follow-up observations of the extended TeV source region with the Chandra X-Ray Observatory and the Very Large Array radio telescope, obtained in order to explore this possibility. Analysis of the CO, H I, and IRAS 100 µm emissions shows that the TeV source region coincides with an outlying subgroup of powerful OB stars that have evacuated or destroyed much of the ambient atomic, molecular, and dust material and that may be related to the very high energy emissions. An interesting supernova-remnant-like structure is also revealed near the TeV source region in the CO, H I, and radio emission maps. Applying a numerical simulation that accurately tracks the radio to gamma-ray emission from primary hadrons as well as primary and secondary e^±, we find that the broadband spectrum of the TeV source region favors a predominantly nucleonic–rather than electronic–origin for the high-energy flux, although deeper X-ray and radio observations will help confirm this. A very reasonable, ∼0.1%, conversion efficiency of Cyg OB2's extreme stellar wind mechanical luminosity to nucleonic acceleration to ∼PeV (10¹⁵ eV) energies is sufficient to explain the multifrequency emissions.