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Volume 358 - 36th International Cosmic Ray Conference (ICRC2019) - GRI - Gamma Ray Indirect
Characterizing the VHE Emission of LS I +61 303 using VERITAS Observations
D. Kieda,* V. Collaboration
*corresponding author
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Pre-published on: 2019 July 22
Published on:
Abstract
The TeV gamma-ray binary LS I +61 303, approximately 2 kpc from Earth, consists of a low mass compact object in an eccentric orbit around a massive Be star. LS I +61 303 exhibits modulated VHE gamma-ray emission around its 26.5 days orbit, with strong-est TeV emission during its apastron passage (orbital phases φ=0.55−0.65). Multiple flaring episodes with nightly flux variability at TeV energies have been observed since its detection in 2006. GeV, X-ray, and radio emission have been detected along the entire orbit, enabling detailed study of the orbital modulation pattern and its super-orbital period.
Previously reported TeV baseline emission and spectral variations may indicate a neutron star flip-flop scenario, in which the binary system switches between accretor and propeller phases at different phases of the orbit.

Since September 2007, VERITAS has observed LS I +61 303 over three additional seasons, accruing 220+ hours of data during different parts of its orbit. In this work, we present a summary of recent and long-term VERITAS observations of LS I +61 303. This analysis includes a discussion of the observed variation of TeV emission during different phases of the orbit, and during different superorbital phases.
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