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.; Buson, S.; 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.; Domínguez, A.; 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.; Gora, D.; Guberman, D.; Hadasch, 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.; 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. et al.
Bibliographical reference
Astronomy and Astrophysics, Volume 591, id.A76, 7 pp.
Advertised on:
6
2016
Journal
Citations
24
Refereed citations
16
Description
Context. The gamma-ray binary LS I +61°303 is a well-established
source from centimeter radio up to very high energy (VHE; E> 100
GeV). The broadband emission shows a periodicity of ~26.5 days,
coincident with the orbital period. A longer (super-orbital) period of
1667 ± 8 days was proposed from radio variability and confirmed
using optical and high-energy (HE; E> 100 MeV) gamma-ray
observations. In this paper, we report on a four-year campaign performed
by MAGIC together with archival data concentrating on a search for a
long-timescale signature in the VHE emission from LS I +61°303. Aims: We focus on the search for super-orbital modulation of the VHE
emission, similar to that observed at other energies, and on the search
for correlations between TeV emission and an optical determination of
the extension of the circumstellar disk. Methods: A four-year
campaign has been carried out using the MAGIC telescopes. The source was
observed during the orbital phases when the periodic VHE outbursts have
occurred (φ = 0.55-0.75, one orbit = 26.496 days). Additionally, we
included archival MAGIC observations and data published by the VERITAS
collaboration in these studies. For the correlation studies, LS I
+61°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. Results: The TeV flux of the
periodical outburst in orbital phases φ = 0.5-0.75 was found to
show yearly variability consistent with the long-term modulation of ~4.5
years found in the radio band. This modulation of the TeV flux can be
well described by a sine function with a best-fit period of 1610
± 58 days. The complete data, including archival observations,
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 Hα fluxes.