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.
4.5 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF MRK 421 DURING THE ARGO-YBJ AND FERMI COMMON OPERATION TIME / Iuppa, Roberto; ARGO YBJ, Collaboration. - In: ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES. - ISSN 0067-0049. - 222:1(2016), pp. 1-17.
|Titolo:||4.5 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF MRK 421 DURING THE ARGO-YBJ AND FERMI COMMON OPERATION TIME|
|Autori:||Iuppa, Roberto; ARGO YBJ, Collaboration|
|Titolo del periodico:||ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES|
|Anno di pubblicazione:||2016|
|Numero e parte del fascicolo:||1|
|Codice identificativo Scopus:||2-s2.0-84955476638|
|Codice identificativo ISI:||WOS:000368982300006|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.3847/0067-0049/222/1/6|
|Citazione:||4.5 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF MRK 421 DURING THE ARGO-YBJ AND FERMI COMMON OPERATION TIME / Iuppa, Roberto; ARGO YBJ, Collaboration. - In: ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES. - ISSN 0067-0049. - 222:1(2016), pp. 1-17.|
|Appare nelle tipologie:||03.1 Articolo su rivista (Journal article)|
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