Super-orbital variability of LS I +61°303 at TeV energies
Creators: name: MAGIC Collaboration
name: Ahnen, M. L.
name: Ansoldi, S.
name: Antonelli, L. A.
name: Antoranz, P.
name: Babic, A.
name: Banerjee, B.
name: Bangale, P.
name: de Almeida, U. Barres
name: Barrio, J. A.
name: González, J. Becerra
name: Bednarek, W.
name: Bernardini, E.
name: Biasuzzi, B.
name: Biland, A.
name: Blanch, O.
name: Bonnefoy, S.
name: Bonnoli, G.
name: Borracci, F.
name: Bretz, T.
name: Buson, S.
name: Carosi, A.
name: Chatterjee, A.
name: Clavero, R.
name: Colin, P.
name: Colombo, E.
name: Contreras, J. L.
name: Cortina, J.
name: Covino, S.
name: Da Vela, P.
name: Dazzi, F.
name: De Angelis, A.
name: De Lotto, B.
name: Wilhelmi, E. de Oña
name: Mendez, C. Delgado
name: Di Pierro, F.
name: Domínguez, A.
name: Prester, D. Dominis
name: Dorner, D.
name: Doro, M.
name: Einecke, S.
name: Glawion, D. Eisenacher
name: Elsaesser, D.
name: Fernández-Barral, A.
name: Fidalgo, D.
name: Fonseca, M. V.
name: Font, L.
name: Frantzen, K.
name: Fruck, C.
name: Galindo, D.
name: López, R. J. García
name: Garczarczyk, M.
name: Terrats, D. Garrido
name: Gaug, M.
name: Giammaria, P.
name: Godinović, N.
name: Muñoz, A. González
name: Gora, D.
name: Guberman, D.
name: Hadasch, D.
name: Hahn, A.
name: Hanabata, Y.
name: Hayashida, M.
name: Herrera, J.
name: Hose, J.
name: Hrupec, D.
name: Hughes, G.
name: Idec, W.
name: Kodani, K.
name: Konno, Y.
name: Kubo, H.
name: Kushida, J.
name: La Barbera, A.
name: Lelas, D.
name: Lindfors, E.
name: Lombardi, S.
name: Longo, F.
name: López, M.
name: López-Coto, R.
name: López-Oramas, A.
name: Majumdar, P.
name: Makariev, M.
name: Mallot, K.
name: Maneva, G.
name: Manganaro, M.
name: Mannheim, K.
name: Maraschi, L.
name: Marcote, B.
name: Mariotti, M.
name: Martínez, M.
name: Mazin, D.
name: Menzel, U.
name: Miranda, J. M.
name: Mirzoyan, R.
name: Moralejo, A.
name: Moretti, E.
name: Nakajima, D.
name: Neustroev, V.
name: Niedzwiecki, A.
name: Rosillo, M. Nievas
name: Nilsson, K.
name: Nishijima, K.
name: Noda, K.
name: Orito, R.
name: Overkemping, A.
name: Paiano, S.
name: Palacio, J.
name: Palatiello, M.
name: Paneque, D.
name: Paoletti, R.
name: Paredes, J. M.
name: Paredes-Fortuny, X.
name: Pedaletti, G.
name: Persic, M.
name: Poutanen, J.
name: Moroni, P. G. Prada
name: Prandini, E.
name: Puljak, I.
name: Rhode, W.
name: Ribó, M.
name: Rico, J.
name: Garcia, J. Rodriguez
name: Saito, T.
name: Satalecka, K.
name: Schultz, C.
name: Schweizer, T.
name: Shore, S. N.
name: Sillanpää, A.
name: Sitarek, J.
name: Snidaric, I.
name: Sobczynska, D.
name: Stamerra, A.
name: Steinbring, T.
name: Strzys, M.
name: Takalo, L.
name: Takami, H.
name: Tavecchio, F.
name: Temnikov, P.
name: Terzić, T.
name: Tescaro, D.
name: Teshima, M.
name: Thaele, J.
name: Torres, D. F.
name: Toyama, T.
name: Treves, A.
name: Verguilov, V.
name: Vovk, I.
name: Ward, J. E.
name: Will, M.
name: Wu, M. H.
name: Zanin, R.
name: Casares, J.
name: Herrero, A.
Publisher: name: arXiv
Year: 2016
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: The gamma-ray binary LS I +61$^{\circ}$303 is a well established source from centimeter radio up to very high energy (VHE; E$&gt;$100 GeV). Its broadband emission shows a periodicity of $\sim$26.5 days, coincident with the orbital period. A longer (super-orbital) period of 1667 $\pm$ 8 days was discovered in radio and confirmed in optical and high energy (HE; E&gt;100 MeV) gamma-ray observations. We present a four-year campaign performed by MAGIC together with archival data concentrating on a search for a long timescale signature in the VHE emission. We focus on the search for super-orbital modulation of the VHE peak and on the search for correlations between TeV emission and optical determination of the extension of the circumstellar disk. A four-year campaign has been carried out by MAGIC. The source was observed during the orbital phases when the periodic VHE outbursts have occurred ($ϕ$=0.55-0.75). Additionally, we included archival MAGIC observations and data published by the VERITAS collaboration in these studies. For the correlation studies, LS I +61$^{\circ}$303 has also been observed during the orbital phases where sporadic VHE emission had been detected in the past ($ϕ$=0.75-1.0). These MAGIC observations were simultaneous with optical spectroscopy from the LIVERPOOL telescope. The TeV flux of the periodical outburst in orbital phases $ϕ$=0.5--0.75 was found to show yearly variability consistent with the $\sim$4.5 years long-term modulation found in the radio band. This modulation of the TeV flux can be well described by a sine function with the best fit period of $1610\pm 58$ days. The complete dataset span two super-orbital periods. There is no evidence for a correlation between the TeV emission and the mass-loss rate of the Be star but this may be affected by the strong, short timescale (as short as intra-day) variation displayed by the H$α$ fluxes.
description: 7 pages, 4 figures, to be published in A&amp;A