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Title: Fermi large area telescope observations of Markarian 421: the missing piece of its spectral energy distribution
Author: Bordas Coma, Pol
Bosch i Ramon, Valentí
Moldón Vara, Francisco Javier
Paredes i Poy, Josep Maria
Ribó Gomis, Marc
Zabalza de Torres, Víctor
Keywords: Acceleradors de partícules
Galàxies actives
Raigs gamma
Particle accelerators
Active galaxies
Gamma rays
Issue Date: 1-Aug-2011
Publisher: Institute of Physics (IOP)
Abstract: We report on the gamma-ray activity of the high-synchrotron-peaked BL Lacertae object Mrk 421 during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) gamma-ray spectrum above 0.3 GeV can be well-described by a power-law function with photon index Gamma=1.78 +/- 0.02 and average photon flux F(>0.3 GeV)=(7.23 +/- 0.16) x 10^{-8} ph cm^{-2} s^{-1}. Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on 7-day-long time intervals, showing significant variations in the photon flux (up to a factor ~3 from the minimum to the maximum flux), but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in gamma-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5-month-long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broad band SED was reproduced with a leptonic (one-zone Synchrotron Self-Compton) and a hadronic model (Synchrotron Proton Blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.
Note: Reproducció del document publicat a:
It is part of: Astrophysical Journal, 2011, vol. 736, num. 131
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ISSN: 0004-637X
Appears in Collections:Articles publicats en revistes (Física Quàntica i Astrofísica)
Articles publicats en revistes (Institut de Ciències del Cosmos (ICCUB))

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