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Title: 4.5 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF MRK 421 DURING THE ARGO-YBJ AND FERMI COMMON OPERATION TIME

We report on the extensive multi-wavelength observations of the blazar Markarian 421 (Mrk 421) covering radio to γ-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 γ-ray flux, while the GeV γ-rays only show a partial correlation with the TeV γ-rays. Radio and UV fluxes seem to be weakly or not correlated with the X-ray and γ-ray fluxes. Seven large flares, including five X-ray flares and two GeV γ-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 flaringmore » episodes, the peak energy in X-rays is observed to increase from sub-keV to a few keV. The TeV γ-ray flux increases up to 0.9–7.2 times the flux of the Crab Nebula. The behavior of GeV γ-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.« less
Authors:
; ; ;  [1] ; ; ;  [2] ; ; ; ; ; ;  [3] ; ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] more »; ; « less
  1. Dipartimento di Fisica dell’Università di Napoli “Federico II,” Complesso Universitario di Monte Sant’Angelo, via Cinthia, I-80126 Napoli (Italy)
  2. Dipartimento Matematica e Fisica “Ennio De Giorgi,” Università del Salento, via per Arnesano, I-73100 Lecce (Italy)
  3. Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, P.O. Box 918, 100049 Beijing (China)
  4. Tibet University, 850000 Lhasa, Xizang (China)
  5. Hebei Normal University, 050024, Shijiazhuang Hebei (China)
  6. Yunnan University, 2 North Cuihu Road, 650091 Kunming, Yunnan (China)
  7. Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata, via della Ricerca Scientifica 1, I-00133 Roma (Italy)
  8. Shandong University, 250100 Jinan, Shandong (China)
  9. Southwest Jiaotong University, 610031 Chengdu, Sichuan (China)
Publication Date:
OSTI Identifier:
22520028
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 222; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; BL LACERTAE OBJECTS; CORRELATIONS; COSMIC X-RAY SOURCES; CRAB NEBULA; EMISSION SPECTRA; ENERGY SPECTRA; GEV RANGE; KEV RANGE; MARKARIAN GALAXIES; MEV RANGE; QUASARS; RELATIVISTIC RANGE; TEV RANGE; VARIATIONS