Mrk 421 active state in 2008: the MAGIC view, simultaneous multi-wavelength observations and SSC model constrained



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Antoranz Canales, Pedro and Barrio Uña, Juan Abel and Contreras González, José Luis and Fonseca González, Mª Victoria and López Moya, Marcos and Miranda Pantoja, José Miguel and Nieto, Daniel and Scapin, Valeria (2012) Mrk 421 active state in 2008: the MAGIC view, simultaneous multi-wavelength observations and SSC model constrained. Astronomy & Astrophysics, 542 . ISSN 0004-6361

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The blazar Markarian 421 is one of the brightest TeV gamma-ray sources of the northern sky. From December 2007 until June 2008 it was intensively observed in the very high energy (VHE, E > 100 GeV) band by the single-dish Major Atmospheric Gamma-ray Imaging Cherenkov telescope (MAGIC-I). Aims. We aimed to measure the physical parameters of the emitting region of the blazar jet during active states.
Methods. We performed a dense monitoring of the source in VHE with MAGIC-I, and also collected complementary data in soft X-rays and optical-UV bands; then, we modeled the spectral energy distributions (SED) derived from simultaneous multi-wavelength data within the synchrotron self-Compton (SSC) framework.
Results. The source showed intense and prolonged.-ray activity during the whole period, with integral fluxes (E > 200 GeV) seldom below the level of the Crab Nebula, and up to 3.6 times this value. Eight datasets of simultaneous optical-UV (KVA, Swift/UVOT), soft X-ray (Swift/XRT) and MAGIC-I VHE data were obtained during different outburst phases. The data constrain the physical parameters of the jet, once the spectral energy distributions obtained are interpreted within the framework of a single-zone SSC leptonic model. Conclusions. The main outcome of the study is that within the homogeneous model high Doppler factors (40 <= delta <= 80) are needed to reproduce the observed SED; but this model cannot explain the observed short time-scale variability, while it can be argued that inhomogeneous models could allow for less extreme Doppler factors, more intense magnetic fields and shorter electron cooling times compatible with hour or sub-hour scale variability.

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© ESO. We would like to thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the Marie Curie program, by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the YIP of the Helmholtz Gemeinschaft, by the DFG Cluster of Excellence "Origin and Structure of the Universe", and by the Polish MNiSzW grant 745/N-HESS-MAGIC/2010/0. We acknowledge insightful and constructive criticism from the anonymous referee.

Uncontrolled Keywords:BL-lacertae objects; Fast tec variability; Gamma-ray emission; Self-compton model; X-ray; Galactic nuclei; Lac objects; Correlated variability; Electron acceleration; Background-radiation.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
Sciences > Physics > Nuclear physics
ID Code:21212
Deposited On:12 Jun 2013 10:37
Last Modified:10 Dec 2018 14:58

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