Context : In 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 > 100GeV ) .
The flux reached a level more than 10 times higher than any previously recorded flaring state of the source .

Aims : Description of 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 at detecting the imprint of the Extragalactic Background Light ( EBL ) in the VHE spectrum of the source , in order 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 .
For the constraining of 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 ( \leq 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 flux changes night by night and also to produce differential energy spectra for all nights of 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 \citep Dominguez2011 , is preferred at the 4.6 \sigma 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 \mu m,4.25 \mu m ] , with a peak value at 1.4 \mu m of \lambda F _ { \lambda } = 12.27 _ { -2.29 } ^ { +2.75 } nW m ^ { -2 } sr ^ { -1 } , including systematics .

Conclusions :