Abstract
The Cygnus-X star-forming region (Cygnus) is the richest star-forming region within 2 kpc of Earth and is home to a wealth of potential cosmic ray accelerators, including supernova remnants, massive star clusters, and pulsar wind nebulae. Over the past five years, discoveries by several gamma-ray observatories sensitive in different energy bands, including the identification by Fermi-LAT of a potential cocoon of freshly accelerated cosmic rays, have pinpointed this region as a unique laboratory for studying the early phases of the cosmic ray life cycle. From 2007 to 2009 VERITAS, a very high energy (VHE; E > 100 GeV) observatory in southern Arizona, undertook an extensive survey of the Cygnus region from 67 to 82 degrees Galactic longitude and from − 1t o 4 degrees in Galactic latitude. In the years since, VERITAS has continued to accumulate data at specific locations within the survey region. We will review the discoveries and insights that this rich dataset has already provided. We will also consider the key role that we expect these data to play in interpreting the complex multiwavelength picture we have of the Cygnus region, particularly in the vicinity of the Cygnus cocoon. As part of this discussion we will summarize ongoing studies of VERITAS data in the Cygnus region, including the development of new data analysis techniques that dramatically increase VERITAS' sensitivity to sources on scales larger than a square degree.
Highlights
Supernova remnants (SNRs) are believed to produce the bulk of Galactic cosmic rays up to the “knee” at 1015 eV, a theory supported by recent GeV and TeV γ -ray and X-ray observations [1,2,3,4,5]
Recent theoretical models indicate that SNRs are PeVatrons for only a brief portion of their life cycle and that the highest energy protons escape early [6]
It is interesting to hunt for other sources of gamma-ray emission that can be identified with populations recently-accelerated cosmic rays, whether these are cosmic rays recently escaped from their accelerator or the result of the collective action of multiple hadronic cosmic ray accelerators
Summary
Supernova remnants (SNRs) are believed to produce the bulk of Galactic cosmic rays up to the “knee” at 1015 eV, a theory supported by recent GeV and TeV γ -ray and X-ray observations [1,2,3,4,5]. Conclusive evidence for protons being accelerated all the way to the knee by SNR shocks has been elusive. Recent theoretical models indicate that SNRs are PeVatrons for only a brief portion of their life cycle (as little as 30 years) and that the highest energy protons escape early [6]. The number of nearby historical supernova remnants is small and the number of potential PeVatrons even smaller. It is interesting to hunt for other sources of gamma-ray emission that can be identified with populations recently-accelerated cosmic rays, whether these are cosmic rays recently escaped from their accelerator or the result of the collective action of multiple hadronic cosmic ray accelerators (e.g. superbubbles)
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