# Associating long-term γ-ray variability with the superorbital period of LS I + 61◦ 303

7 FERMI
CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan
Abstract : Gamma-ray binaries are stellar systems for which the spectral ene rgy distribu- tion (discounting the thermal stellar emission) peaks at high energie s. Detected from radio to TeV gamma rays, the γ -ray binary LS I +61 ◦ 303 is highly variable across all frequencies. One aspect of this system's variability is the modula- tion of its emission with the timescale set by the ∼ 26 . 4960-day orbital period. Here we show that, during the time of our observations, the γ -ray emission of LS I +61 ◦ 303 also presents a sinusoidal variability consistent with the previou sly- known superorbital period of 1667 days. This modulation is more pro minently seen at orbital phases around apastron, whereas it does not intr oduce a visible change close to periastron. It is also found in the appearance and d isappearance of variability at the orbital period in the power spectrum of the data . This be- havior could be explained by a quasi-cyclical evolution of the equator ial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. These findings open the possibility to use γ -ray observations to study the outflows of massive stars in eccentric binary systems.
Document type :
Journal articles
Domain :

http://hal.in2p3.fr/in2p3-00915658
Contributor : Nathalie Martin <>
Submitted on : Monday, December 9, 2013 - 10:57:55 AM
Last modification on : Monday, December 7, 2020 - 11:00:03 PM

### Citation

Markus Ackermann, Marco Ajello, Jean Ballet, Guido Barbiellini, D. Bastieri, et al.. Associating long-term γ-ray variability with the superorbital period of LS I + 61◦ 303. The Astrophysical journal letters, Bristol : IOP Publishing, 2013, 773, pp.L19. ⟨10.1088/2041-8205/773/2/L19⟩. ⟨in2p3-00915658⟩

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