MAGIC observations of the February 2014 flare of 1ES 1011+496 and ensuing constraint of the EBL density



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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 Nievas Rosillo, Miguel and Satalecka, Konstanzja and otros, ... (2016) MAGIC observations of the February 2014 flare of 1ES 1011+496 and ensuing constraint of the EBL density. Astronomy & Astrophysics, 590 . ISSN 1432-0746

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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 (< 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 di_erential 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 (Domínguez et al. 2011), is preferred at the 4:6 σ 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 λF_ = 12:27^(+2:75)_ (-2:29) nW m^(-2) sr^(-1), including systematics.

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© ESO, 2016. Artículo firmado por 148 autores. We would like to thank the Instituto de Astrofísica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The financial support of the German BMBF and MPG, the Italian INFN and INAF, the Swiss National Fund SNF, the ERDF under the Spanish MINECO, and the Japanese JSPS and MEXT is gratefully acknowledged. This work was also supported by the Centro de Excelencia Severo Ochoa SEV-2012-0234, CPAN CSD2007-00042, and MultiDark CSD2009-00064 projects of the Spanish Consolider Ingenio 2010 programme, by grant 268740 of the Academy of Finland, by the Croatian Science Foundation (HrZZ) Project 09/176 and the University of Rijeka Project, by the DFG Collaborative Research Centers SFB823/C4 and SFB876/C3, and by the Polish MNiSzW grant 745/N-HESS MAGIC/2010/0. We thank the anonymous referee for a thorough review and a very constructive list.

Uncontrolled Keywords:Extragalactic background light; Telescope imaging spectrograph; Spitze-space-telescope; Micron surce counts; Energy gamma-rays; Dirbe Minus 2MASS; 3.5 Mu-M; Number counts; Galaxy counts; TeV blazars.
Subjects:Sciences > Physics > Electricity
Sciences > Physics > Electronics
Sciences > Physics > Nuclear physics
ID Code:39034
Deposited On:05 Oct 2016 07:31
Last Modified:10 Dec 2018 14:57

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