Long-term Monitoring on Mrk 501 for Its VHE gamma Emission and a Flare in October 2011
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: Cardarelli, R.
name: Catalanotti, S.
name: Cattaneo, C.
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. DAl
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: 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, 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: Pagliaro, A.
name: Panareo, M.
name: Panico, B.
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: 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: 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: 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: 2012
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: As one of the brightest active blazars in both X-ray and very high energy $γ$-ray bands, Mrk 501 is very useful for physics associated with jets from AGNs. The ARGO-YBJ experiment is monitoring it for $γ$-rays above 0.3 TeV since November 2007. Starting from October 2011 the largest flare since 2005 is observed, which lasts to about April 2012. In this paper, a detailed analysis is reported. During the brightest $γ$-rays flaring episodes from October 17 to November 22, 2011, an excess of the event rate over 6 $σ$ is detected by ARGO-YBJ in the direction of Mrk 501, corresponding to an increase of the $γ$-ray flux above 1 TeV by a factor of 6.6$\pm$2.2 from its steady emission. In particular, the $γ$-ray flux above 8 TeV is detected with a significance better than 4 $σ$. Based on time-dependent synchrotron self-Compton (SSC) processes, the broad-band energy spectrum is interpreted as the emission from an electron energy distribution parameterized with a single power-law function with an exponential cutoff at its high energy end. The average spectral energy distribution for the steady emission is well described by this simple one-zone SSC model. However, the detection of $γ$-rays above 8 TeV during the flare challenges this model due to the hardness of the spectra. Correlations between X-rays and $γ$-rays are also investigated.
description: have been accepted for publication at ApJ