Bibcode
Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biasuzzi, B.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Chatterjee, A.; Clavero, R.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Lotto, B.; de Oña Wilhelmi, E.; Delgado Mendez, C.; Di Pierro, F.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher Glawion, D.; Elsaesser, D.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; Galindo, D.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Giammaria, P.; Godinović, N.; González Muñoz, A.; Guberman, D.; Hahn, A.; Hanabata, Y.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Hughes, G.; Idec, W.; Kodani, K.; Konno, Y.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lindfors, E.; Lombardi, S.; Longo, F.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Majumdar, P.; Makariev, M.; Mallot, K.; Maneva, G.; Manganaro, M.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Moretti, E.; Nakajima, D.; Neustroev, V.; Niedzwiecki, A.; Nievas Rosillo, M.; Nilsson, K.; Nishijima, K.; Noda, K. et al.
Bibliographical reference
Astronomy and Astrophysics, Volume 590, id.A24, 8 pp.
Advertised on:
5
2016
Journal
Citations
51
Refereed citations
49
Description
Context. During February-March 2014, the MAGIC telescopes observed the
high-frequency peaked BL Lac 1ES 1011+496 (z = 0.212) in flaring state
at very-high energy (VHE, E> 100 GeV). The flux reached a level of
more than ten times higher than any previously recorded flaring state of
the source. Aims: To describe the characteristics of the flare
presenting the light curve and the spectral parameters of the night-wise
spectra and the average spectrum of the whole period. From these data we
aim to detect the imprint of the extragalactic background light (EBL) in
the VHE spectrum of the source, to constrain its intensity in the
optical band. Methods: We analyzed the gamma-ray data from the
MAGIC telescopes using the standard MAGIC software for the production of
the light curve and the spectra. To constrain the EBL, we implement the
method developed by the H.E.S.S. collaboration, in which the intrinsic
energy spectrum of the source is modeled with a simple function (≤4
parameters), and the EBL-induced optical depth is calculated using a
template EBL model. The likelihood of the observed spectrum is then
maximized, including a normalization factor for the EBL opacity among
the free parameters. Results: The collected data allowed us to
describe the night-wise flux changes and also to produce differential
energy spectra for all nights in the observed period. The estimated
intrinsic spectra of all the nights could be fitted by power-law
functions. Evaluating the changes in the fit parameters, we conclude
that the spectral shape for most of the nights were compatible,
regardless of the flux level, which enabled us to produce an average
spectrum from which the EBL imprint could be constrained. The likelihood
ratio test shows that the model with an EBL density 1.07 (-0.20,
+0.24)stat+sys, relative to the one in the tested EBL
template, is preferred at the 4.6σ level to the no-EBL hypothesis,
with the assumption that the intrinsic source spectrum can be modeled as
a log-parabola. This would translate into a constraint of the EBL
density in the wavelength range [0.24 μm, 4.25 μm], with a peak
value at 1.4 μm of λFλ =
12.27-2.29+2.75 nW m-2 sr-1,
including systematics.