Bibcode
Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Boller, A.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; de Oña Wilhelmi, E.; Delgado Mendez, C.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hildebrand, D.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Kadenius, V.; Kellermann, H.; Knoetig, M. L.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Noda, K.; Orito, R.; Overkemping, A. et al.
Bibliographical reference
Astronomy and Astrophysics, Volume 578, id.A22, 26 pp.
Advertised on:
6
2015
Journal
Citations
114
Refereed citations
101
Description
Context. Because of its proximity, Mrk 421 is one of the best sources on
which to study the nature of BL Lac objects. Its proximity allows us to
characterize its broadband spectral energy distribution (SED).
Aims: The goal is to better understand the mechanisms responsible for
the broadband emission and the temporal evolution of Mrk 421. These
mechanisms may also apply to more distant blazars that cannot be studied
with the same level of detail. Methods: A flare occurring in
March 2010 was observed for 13 consecutive days (from MJD 55 265 to MJD
55 277) with unprecedented wavelength coverage from radio to very high
energy (VHE; E> 100 GeV) γ-rays with MAGIC, VERITAS, Whipple,
Fermi-LAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio
telescopes. We modeled the day-scale SEDs with one-zone and two-zone
synchrotron self-Compton (SSC) models, investigated the physical
parameters, and evaluated whether the observed broadband SED variability
can be associated with variations in the relativistic particle
population. Results: The activity of Mrk 421 initially was high
and then slowly decreased during the 13-day period. The flux variability
was remarkable at the X-ray and VHE bands, but it was minor or not
significant at the other bands. The variability in optical polarization
was also minor. These observations revealed an almost linear correlation
between the X-ray flux at the 2-10 keV band and the VHE γ-ray flux
above 200 GeV, consistent with the γ-rays being produced by
inverse-Compton scattering in the Klein-Nishina regime in the framework
of SSC models. The one-zone SSC model can describe the SED of each day
for the 13 consecutive days reasonably well, which once more shows the
success of this standard theoretical scenario to describe the SEDs of
VHE BL Lacs such as Mrk 421. This flaring activity is also very well
described by a two-zone SSC model, where one zone is responsible for the
quiescent emission, while the other smaller zone, which is spatially
separated from the first, contributes to the daily variable emission
occurring at X-rays and VHE γ-rays. The second blob is assumed to
have a smaller volume and a narrow electron energy distribution with 3
× 104<γ< 6 × 105, where
γ is the Lorentz factor of the electrons. Such a two-zone scenario
would naturally lead to the correlated variability at the X-ray and VHE
bands without variability at the optical/UV band, as well as to shorter
timescales for the variability at the X-ray and VHE bands with respect
to the variability at the other bands. Conclusions: Both the
one-zone and the two-zone SSC models can describe the daily SEDs via the
variation of only four or five model parameters, under the hypothesis
that the variability is associated mostly with the underlying particle
population. This shows that the particle acceleration and cooling
mechanism that produces the radiating particles might be the main
mechanism responsible for the broadband SED variations during the
flaring episodes in blazars. The two-zone SSC model provides a better
agreement with the observed SED at the narrow peaks of the low- and
high-energy bumps during the highest activity, although the reported
one-zone SSC model could be further improved by varying the parameters
related to the emitting region itself (δ, B and R), in addition to
the parameters related to the particle population.
Appendices are available in electronic form at http://www.aanda.orgMulti-wavelength
light curves (data in Fig. 1) and broadband spectral energy
distributions (the data in Figs. 7, 8a-9f, 12a-13f) are only available
at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A22
Related projects
Particle Astrophysics
The MAGIC Collaboration is integrated by 20 research institutes and university departments from Armenia, Bulgaria, Finland, Germany, Italy, Poland, Spain, Switzerland and USA. The collaboration comprises two 17m diameter telescopes, located at the Roque de los Muchachos Observatory, designed to measure the Cherenkov radiation associated with
Ramón
García López