Long-term monitoring of the TeV emission from Mrk 421 with the ARGO-YBJ experiment
Creators: name: YBJ Collaboration
name: Bartoli, B.
name: Bernardini, P.
name: Bi, X. J.
name: Bleve, C.
name: Bolognino, I.
name: Branchini, P.
name: Budano, A.
name: Melcarne, A. K. Calabrese
name: Camarri, P.
name: Cao, Z.
name: Cappa, A.
name: Cardarelli, R.
name: Catalanotti, S.
name: Cattaneo, C.
name: Celio, P.
name: Chen, S. Z.
name: Chen, T. L.
name: Chen, Y.
name: Creti, P.
name: Cui, S. W.
name: Dai, B. Z.
name: Staiti, G. D'Alí
name: Danzengluobu
name: Dattoli, M.
name: De Mitri, I.
name: Piazzoli, B. D'Ettorre
name: Di Girolamo, T.
name: Ding, X. H.
name: Di Sciascio, G.
name: Feng, C. F.
name: Feng, Zhaoyang
name: Feng, Zhenyong
name: Galeazzi, F.
name: Galeotti, P.
name: Giroletti, E.
name: Gou, Q. B.
name: Guo, Y. Q.
name: He, H. H.
name: Hu, Haibing
name: Hu, Hongbo
name: Huang, Q.
name: Iacovacci, M.
name: Iuppa, R.
name: James, I.
name: Jia, H. Y.
name: Labaciren
name: Li, H. J.
name: Li, J. Y.
name: Li, X. X.
name: Liguori, G.
name: Liu, C.
name: Liu, C. Q.
name: Liu, J.
name: Liu, M. Y.
name: Lu, H.
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: Pagliaro, A.
name: Panareo, M.
name: Panico, B.
name: Perrone, L.
name: Pistilli, P.
name: Qu, X. B.
name: Rossi, E.
name: Ruggieri, F.
name: Salvini, P.
name: Santonico, R.
name: Shen, P. R.
name: Sheng, X. D.
name: Shi, F.
name: Stanescu, C.
name: Surdo, A.
name: Tan, Y. H.
name: Vallania, P.
name: Vernetto, S.
name: Vigorito, C.
name: Wang, B.
name: Wang, H.
name: Wu, C. Y.
name: Wu, H. R.
name: Xu, B.
name: Xue, L.
name: Yan, Y. X.
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, Jilong
name: Zhang, Jianli
name: Zhang, L.
name: Zhang, P.
name: Zhang, X. Y.
name: Zhang, Y.
name: Zhaxiciren
name: Zhaxisangzhu
name: Zhou, X. X.
name: Zhu, F. R.
name: Zhu, Q. Q.
name: Zizzi, G.
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: ARGO-YBJ is an air shower detector array with a fully covered layer of resistive plate chambers. It is operated with a high duty cycle and a large field of view. It continuously monitors the northern sky at energies above 0.3 TeV. In this paper, we report a long-term monitoring of Mrk 421 over the period from 2007 November to 2010 February. This source was observed by the satellite-borne experiments Rossi X-ray Timing Explorer and Swift in the X-ray band. Mrk 421 was especially active in the first half of 2008. Many flares are observed in both X-ray and gamma-ray bands simultaneously. The gamma-ray flux observed by ARGO-YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and gamma-ray photons longer than 1 day is found. The evolution of the spectral energy distribution is investigated by measuring spectral indices at four different flux levels. Hardening of the spectra is observed in both X-ray and gamma-ray bands. The gamma-ray flux increases quadratically with the simultaneously measured X-ray flux. All these observational results strongly favor the synchrotron self-Compton process as the underlying radiative mechanism.
description: 30 pages, 8 figures