Identification of the TeV Gamma-Ray Source ARGO J2031+4157 with the Cygnus Cocoon
Abstract
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° × 10°, finding a source extension σext= 1.°8 ± 0.°5. The observed differential energy spectrum is dN/dE = (2.5 ± 0.4) × 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2014
- DOI:
- 10.1088/0004-637X/790/2/152
- arXiv:
- arXiv:1406.6436
- Bibcode:
- 2014ApJ...790..152B
- Keywords:
-
- acceleration of particles;
- cosmic rays;
- gamma rays: general;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 16 pages, 3 figures, has been accepted by ApJ for publication