Identification of the TeV Gamma-ray Source ARGO J2031+4157 with the Cygnus Cocoon
Creators: name: YBJ Collaboration
name: Bartoli, B.
name: Bernardini, P.
name: Bi, X. J.
name: Branchini, P.
name: Budano, A.
name: Camarri, P.
name: Cao, Z.
name: Cardarelli, R.
name: Catalanotti, S.
name: Chen, S. Z.
name: Chen, T. L.
name: Creti, P.
name: Cui, S. W.
name: Dai, B. Z.
name: DAmone, A.
name: Danzengluobu
name: De Mitri, I.
name: Piazzoli, B. DEttorre
name: Di Girolamo, T.
name: Di Sciascio, G.
name: Feng, C. F.
name: Feng, Zhaoyang
name: Feng, Zhenyong
name: Gou, Q. B.
name: Guo, Y. Q.
name: He, H. H.
name: Hu, Haibing
name: Hu, Hongbo
name: Iacovacci, M.
name: Iuppa, R.
name: Jia, H. Y.
name: Labaciren
name: Li, H. J.
name: Liguori, G.
name: Liu, C.
name: Liu, J.
name: Liu, M. Y.
name: Lu, H.
name: Ma, L. L.
name: Ma, X. H.
name: Mancarella, G.
name: Mari, S. M.
name: Marsella, G.
name: Martello, D.
name: Mastroianni, S.
name: Montini, P.
name: Ning, C. C.
name: Panareo, M.
name: Perrone, L.
name: Pistilli, P.
name: Ruggieri, F.
name: Salvini, P.
name: Santonico, R.
name: Shen, P. R.
name: Sheng, X. D.
name: Shi, F.
name: Surdo, A.
name: Tan, Y. H.
name: Vallania, P.
name: Vernetto, S.
name: Vigorito, C.
name: Wang, H.
name: Wu, C. Y.
name: Wu, H. R.
name: Xue, L.
name: Yang, Q. Y.
name: Yang, X. C.
name: Yao, Z. G.
name: Yuan, A. F.
name: Zha, M.
name: Zhang, H. M.
name: Zhang, L.
name: Zhang, P.
name: Zhang, X. Y.
name: Zhang, Y.
name: Zhao, J.
name: Zhaxiciren
name: Zhaxisangzhu
name: Zhou, X. X.
name: Zhu, F. R.
name: Zhu, Q. Q.
name: Zizzi, G.
Publisher: name: arXiv
Year: 2014
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 November 2007 to January 2013, 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 $10^{\circ}\times 10^{\circ}$, finding a source extension $σ_{ext}$= 1$^{\circ}$.8$\pm$0$^{\circ}$.5. The observed differential energy spectrum is $dN/dE =(2.5\pm0.4) \times 10^{-11}(E/1 TeV)^{-2.6\pm0.3}$ 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 indicates that the particle acceleration inside a superbubble is similar to that in a 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.
description: 16 pages, 3 figures, has been accepted by ApJ for publication