Abstract

We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to gamma-rays, during the 4.5 year period of ARGO-YBJ and Fermi common operation time, from 2008 August to 2013 February. These long-term observations, extending over an energy range of 18 orders of magnitude, provide a unique chance to study the variable emission of Mrk 421. In particular, due to the ARGO-YBJ and Fermi data, the entire. energy range from 100 MeV to 10 TeV is covered without any gap. In the observation period, Mrk 421 showed both low-and high-activity states at all wavebands. The correlations among flux variations in different wavebands were analyzed. The X-ray flux is clearly correlated with the TeV gamma-ray flux, while the GeV gamma-rays only show a partial correlation with the TeV gamma-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and gamma-ray fluxes. Seven large flares, including five X-ray flares and two GeV gamma-ray flares with variable durations (3-58 days), and one X-ray outburst phase were identified and used to investigate the variation of the spectral energy distribution with respect to a relative quiescent phase. During the outburst phase and the seven flaring episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV gamma-ray flux increases up to 0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV gamma-rays is found to vary depending on the flare, a feature that leads us to classify flares into three groups according to the GeV flux variation. Finally, the one-zone synchrotron self-Compton model was adopted to describe the emission spectra. Two out of three groups can be satisfactorily described using injected electrons with a power-law spectral index around 2.2, as expected from relativistic diffuse shock acceleration, whereas the remaining group requires a harder injected spectrum. The underlying physical mechanisms responsible for different groups may be related to the acceleration process or to the environment properties.

Autore Pugliese

• Bernardini Paolo , Mancarella Giovanni , Perrone Lorenzo , Marsella Giovanni

Tutti gli autori

• Bartoli, B. , Bernardini, Paolo , Xje, X. J. E , Cao, Z. E , Catalanotti, S. , Chen, S. Z. , Chen, T. L. , Cui, S. W. , Dai, B. Z. , D'Amone, Antonio , Danzengluobu, , DE MITRI, Ivan , Piazzoli, B. D. , Di Girolamo, T. , Di Sciascio, G. , Feng, C. F. , Feng, Z. , Gou, Q. B. , Guo, Y. Q. , H. H., He , Hu, H. , Hu, H. , Iacovacci, M. , Iuppa, R. , Jia, H. Y. , Labaciren, , H. J., Li , Liu, C. , Liu, J. , Liu, M. Y. , Lu, H. , L. L., Ma , X. H., Ma , Mancarella, Giovanni , Mari, S. M. , Marsella, Giovanni , Mastroianni, S. , Montini, P. , Ning, C. C. , Perrone, Lorenzo , Pistilli, P. , Salvini, P. , Santonico, R. , Shen, P. R. , Sheng, X. D. , Shi, F. , Surdo, A. , Tan, Y. H. , Vallania, P. , Vernetto, S. , Vigorito, C. , Wang, H. , C. Y., Wu , H. R., Wu , Xue, L. , Yang, Q. Y. , Yang, X. C. , Yao, Z. G. E , Yuan, , A. F., , Zha, M. , Zhang, H. M. , Zhang, L. , Zhang, X. Y. , Zhang, Y. , Zhao, J. , Zhaxiciren, , Zhaxisangzhu, , Zhou, X. X. , Zhu, F. R. , Zhu, Q. Q.

Titolo volume/Rivista

ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES

Anno di pubblicazione

2016

ISSN

0067-0049

ISBN

Non Disponibile

Numero di citazioni Wos

15

Ultimo Aggiornamento Citazioni

28/04/2018

Numero di citazioni Scopus

14

Ultimo Aggiornamento Citazioni

28/04/2018

Settori ERC

Non Disponibile

Codici ASJC

Non Disponibile