Journal
ASTROPHYSICAL JOURNAL
Volume 790, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/790/2/152
Keywords
acceleration of particles; cosmic rays; gamma rays: general
Categories
Funding
- NSFC [10120130794, 11205165, 11375210]
- Chinese Ministry of Science and Technology
- Chinese Academy of Sciences
- Key Laboratory of Particle Astrophysics, CAS
- Italy by the Istituto Nazionale di Fisica Nucleare (INFN)
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The extended TeV gamma-ray source ARGO J2031+4157 (or MGRO J2031+41) is positionally consistent with the Cygnus Cocoon discovered by Fermi-LAT at GeV energies in the Cygnus superbubble. Reanalyzing the ARGO-YBJ data collected from 2007 November to 2013 January, the angular extension and energy spectrum of ARGO J2031+4157 are evaluated. After subtracting the contribution of the overlapping TeV sources, the ARGO-YBJ excess map is fitted with a two-dimensional Gaussian function in a square region of 10 degrees x 10 degrees, finding a source extension sigma(ext) = 1 degrees.8 +/- 0 degrees.5. The observed differential energy spectrum is dN/dE = (2.5 +/- 0.4) x 10(-11)(E/1 TeV)(-2.6 +/- 0.3) photons cm(-2) s(-1) TeV-1, in the energy range 0.2-10 TeV. The angular extension is consistent with that of the Cygnus Cocoon as measured by Fermi-LAT and the spectrum also shows a good connection with the one measured in the 1-100 GeV energy range. These features suggest to identify ARGO J2031+4157 as the counterpart of the Cygnus Cocoon at TeV energies. The Cygnus Cocoon, located in the star-forming region of Cygnus X, is interpreted as a cocoon of freshly accelerated cosmic rays related to the Cygnus superbubble. The spectral similarity with supernova remnants (SNRs) indicates that the particle acceleration inside a superbubble is similar to that in an SNR. The spectral measurements from 1 GeV to 10 TeV allows for the first time to determine the possible spectrum slope of the underlying particle distribution. A hadronic model is adopted to explain the spectral energy distribution.
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