Long-term monitoring of the TeV emission from Mrk 421 with the ARGO-YBJ experiment

📝 Abstract

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.

💡 Analysis

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.

📄 Content

arXiv:1106.0896v1 [astro-ph.HE] 5 Jun 2011 Long-term monitoring of the TeV emission from Mrk 421 with the ARGO-YBJ experiment B. Bartoli1,2, P. Bernardini3,4, X.J. Bi5, C. Bleve3,4, I. Bolognino6,7, P. Branchini8, A. Budano8, A.K. Calabrese Melcarne9, P. Camarri10,11, Z. Cao5, A. Cappa12,13, R. Cardarelli11, S. Catalanotti1,2, C. Cattaneo7, P. Celio8,14, S.Z. Chen0,5 ,T.L. Chen15, Y. Chen5, P. Creti4, S.W. Cui16, B.Z. Dai17, G. D’Al´ı Staiti18,19, Danzengluobu15, M. Dattoli12,13,20, I. De Mitri3,4, B. D’Ettorre Piazzoli1,2, T. Di Girolamo1,2, X.H. Ding15, G. Di Sciascio11, C.F. Feng21, Zhaoyang Feng5, Zhenyong Feng22, F. Galeazzi8, P. Galeotti13,20, E. Giroletti6,7, Q.B. Gou5, Y.Q. Guo5, H.H. He5, Haibing Hu15, Hongbo Hu5, Q. Huang22, M. Iacovacci1,2, R. Iuppa10,11, I. James8,14, H.Y. Jia22, Labaciren15, H.J. Li15, J.Y. Li21, X.X. Li5, G. Liguori6,7, C. Liu5, C.Q. Liu17, J. Liu17, M.Y. Liu15, H. Lu5, X.H. Ma5, G. Mancarella3,4, S.M. Mari8,14, G. Marsella4,23, D. Martello3,4, S. Mastroianni2, P. Montini8,14, C.C. Ning15, A. Pagliaro19,24, M. Panareo4,23, B. Panico10,11, L. Perrone4,23, P. Pistilli8,14, X.B. Qu21, E. Rossi2, F. Ruggieri8, P. Salvini7, R. Santonico10,11, P.R. Shen5, X.D. Sheng5, F. Shi5, C. Stanescu8, A. Surdo4, Y.H. Tan5, P. Vallania12,13, S. Vernetto12,13, C. Vigorito13,20, B. Wang5, H. Wang5, C.Y. Wu5, H.R. Wu5, B. Xu22, L. Xue21, Y.X. Yan17, Q.Y. Yang17, X.C. Yang17, Z.G. Yao5, A.F. Yuan15, M. Zha5, H.M. Zhang5, Jilong Zhang5, Jianli Zhang5, L. Zhang17, P. Zhang17, X.Y. Zhang21, Y. Zhang5, Zhaxiciren15, Zhaxisangzhu15, X.X. Zhou22, F.R. Zhu22, Q.Q. Zhu5 and G. Zizzi9 (The ARGO-YBJ Collaboration) 0Corresponding author: S.Z. Chen, chensz@ihep.ac.cn – 2 – 1Dipartimento di Fisica dell’Universita di Napoli “Federico II”, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli, Italy. 2Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Complesso Universitario di Monte Sant’Angelo, via Cinthia, 80126 Napoli, Italy. 3Dipartimento di Fisica dell’Universita del Salento, via per Arnesano, 73100 Lecce, Italy. 4Istituto Nazionale di Fisica Nucleare, Sezione di Lecce, via per Arnesano, 73100 Lecce, Italy. 5Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918, 100049 Beijing, China. 6Dipartimento di Fisica Nucleare e Teorica dell’Universita di Pavia, via Bassi 6, 27100 Pavia, Italy. 7Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, via Bassi 6, 27100 Pavia, Italy. 8Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre, via della Vasca Navale 84, 00146 Roma, Italy. 9Istituto Nazionale di Fisica Nucleare-CNAF, Viale Berti-Pichat 6/2, 40127 Bologna, Italy. 10Dipartimento di Fisica dell’Universita di Roma “Tor Vergata”, via della Ricerca Scien- tifica 1, 00133 Roma, Italy. 11Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy. 12Istituto di Fisica dello Spazio Interplanetario dell’Istituto Nazionale di Astrofisica, corso Fiume 4 - 10133 Torino, Italy. 13Istituto Nazionale di Fisica Nucleare, Sezione di Torino, via P. Giuria 1 - 10125 Torino, Italy. 14Dipartimento di Fisica dell’Universita “Roma Tre”, via della Vasca Navale 84, 00146 – 3 – Received ; accepted Not to appear in Nonlearned J., 45. Roma, Italy. 15Tibet University, 850000 Lhasa, Xizang, China. 16Hebei Normal University, Shijiazhuang 050016, Hebei, China. 17Yunnan University, 2 North Cuihu Rd, 650091 Kunming, Yunnan, China. 18Universita degli Studi di Palermo, Dipartimento di Fisica e Tecnologie Relative, Viale delle Scienze - Edificio 18 - 90128 Palermo, Italy. 19Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Viale A. Doria 6 - 95125 Catania, Italy. 20Dipartimento di Fisica Generale dell’Universita di Torino, via P. Giuria 1 - 10125 Torino, Italy. 21Shandong University, 250100 Jinan - Shandong, China. 22Southwest Jiaotong University - 610031 Chengdu, Sichuan, China. 23Dipartimento di Ingegneria dell’Innovazione, Universita del Salento - 73100 Lecce, Italy. 24Istituto di Astrofisica Spaziale e Fisica Cosmica, Istituto Nazionale di Astrofisica, via La Malfa 153 - 90146 Palermo, Italy. – 4 – ABSTRACT 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 γ-ray bands simultaneously. The γ-ray flux observed by ARGO- YBJ has a clear correlation with the X-ray flux. No lag between the X-ray and γ-ray photons longer than 1 day is found. The evolution of the spectral energy distribution

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