DETECTION OF THE γ-RAY BINARY LS I +61°303 IN A LOW-FLUX STATE AT VERY HIGH ENERGY γ-RAYS WITH THE MAGIC TELESCOPES IN 2009

• Published in: The Astrophysical journal 2012-02, Vol.746 (1), p.1-5
• Main Authors: ALEKSIC, J, ALVAREZ, E. A, BERDYUGIN, A, BERGFR, K, BERNARDINI, E, BILAND, A, BLANCH, O, BOCK, R. K, BOLLER, A, BONNOLI, G, BORLA TRIDON, D, BOSCH-RAMON, V, ANTONELLI, L. A, BRAUN, I, BRETZ, T, CANELLAS, A, CARMONA, E, CAROSI, A, COLIN, P, COLOMBO, E, CONTRERAS, J. L, CORTINA, J, COSSIO, L, ANTORANZ, P, COVINO, S, DAZZI, F, DE ANGELIS, A, DE CANEVA, G, DE CEA DEAL POZO, E, DE LOTTO, B, DELGADO MENDEZ, C, DIAGO ORTEGA, A, DOERT, M, DOMINGUEZ, A, ASENSIO, M, DOMINIS PRESTER, D, DORNER, D, DORO, M, ELSAESSER, D, FERENC, D, FONSECA, M. V, FONT, L, FRUCK, C, GARCIA LOPEZ, R. J, GARCZARCZYK, M, BACKES, M, GARRIDO, D, GIAVITTO, G, GODINOVIC, N, HADASCH, D, HÄFNER, D, HERRERO, A, HILDEBRAND, D, HÖHNE-MÖNCH, D, HOSE, J, HRUPEC, D, BARRIO, J. A, BASTIERI, D, BECERRA GONZALEZ, J, BEDNAREK, W
• Format: Article
• Language: English
• Subjects: Astronomy; Binary systems; Crab nebula; Earth, ocean, space; Exact sciences and technology; Flux; Integrals; Intervals; Orbitals; Stars; Telescopes
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/746/1/80

We present very high energy (E > 100 GeV) gamma -ray observations of the gamma -ray binary system LS I +61[degrees]303 obtained with the MAGIC stereo system between 2009 October and 2010 January. We detect a 6.3[sigma] gamma -ray signal above 400 GeV in the combined data set. The integral flux above an energy of 300 GeV is F(E > 300 GeV) = (1.4 + or - 0.3 sub(stat) + or - 0.4 sub(syst)) x 10 super(-12) cm super(-2) s super(-1), which corresponds to about 1.3% of the Crab Nebula flux in the same energy range. The orbit-averaged flux of LS I +61[degrees]303 in the orbital phase interval 0.6-0.7, where a maximum of the TeV flux is expected, is lower by almost an order of magnitude compared to our previous measurements between 2005 September and 2008 January. This provides evidence for a new low-flux state in LS I +61[degrees]303. We find that the change to the low-flux state cannot be solely explained by an increase of photon-photon absorption around the compact star.