Fermi Gamma-ray Space Telescope

Simultaneous long-term monitoring of LS I +61°303 by OVRO and Fermi-LAT

Frederic Jaron
(Maria Massi, Sebastian Kiehlmann, Talvikki Hovatta)


Previous long-term monitoring programs observing the gamma-ray-loud X-ray binary LS I +61°303 have revealed the presence of a long-term modulation of circa 4.5 yr. After 9 yr of simultaneous monitoring of LS I +61°303 by the Owens Valley Radio Observatory and the Fermi-LAT, two cycles of the long-term period are now available. By performing timing analysis on the radio and the GeV light curves we confirm the presence of previously detected periodicities at both radio and GeV wavelengths. Moreover, we have discovered a phase-offset of the long-term modulation between the radio and the GeV data. We discuss this offset in a scenario where radio and GeV emission originate in different locations along a precessing jet.