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Journal Article

Revisiting LS I +61 303 with VLBI astrometry


Shao,  L.
Astrophysical and Cosmological Relativity, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;

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Wu, Y. W., Torricelli-Ciamponi, G., Massi, M., Reid, M. J., Zhang, B., Shao, L., et al. (2018). Revisiting LS I +61 303 with VLBI astrometry. Monthly Notices of the Royal Astronomical Society: Letters, 474, 4245-4253. doi:10.1093/mnras/stx3003.

Cite as: http://hdl.handle.net/21.11116/0000-0000-ADF1-D
We conducted multi-epoch VLBA phase reference observations of LS I +61 303 in order to study its precessing radio jet. Compared to similar observations in 2006, we find that the observed elliptical trajectory of emission at 8.4 GHz repeats after the 9-year gap. The accurate alignment of the emission patterns yields a precession period of 26.926 +- 0.005 d, which is consistent with that determined by Lomb-Scargle analysis of the radio light curve. We analytically model the projection on the sky plane of the peak position of a precessing, synchrotron-emitting jet, which traces an elliptical trajectory on the sky. Comparing the simulation with the VLBA astrometry we improve our knowledge of the geometry of the system.We measure the LS I +61 303 absolute proper motion to be -0.150 +- 0.006 mas/yr eastward and -0.264 +- 0.006 mas/yr northward. Removing Galactic rotation, this reveals a small, < 20 km/s, non-circular motion, which indicates a very low kick velocity when the black hole was formed.