Radio pulsations from a neutron star within the gamma-ray binary LS I+61° 303

LS I +61 degrees 303 is one of the rare gamma-ray binaries(1) that emit most of their luminosity in photons with energies beyond 100 MeV (ref.(2)). It is well characterized-the similar to 26.5 day orbital period is clearly detected at many wavelengths(2-4)-and other aspects of its multifrequency behaviour make it the most interesting example of its class. The morphology of high-resolution radio images changes with orbital phase, displaying a cometary tail pointing away from the high-mass star components and LS I +61 degrees 303 also shows superorbital variability(3,6-9). A couple of energetic (similar to 10(37) erg s(-1)), short, magnetar-like bursts have been plausibly ascribed to it(10)(-13). Although the phenomenology of LS I +61 degrees 303 has been the subject of theoretical scrutiny for decades, there has been a lack of certainty regarding the nature of the compact object in the binary that has hampered our understanding of the source. Here, using observations with the Five-hundred-meter Aperture Spherical radio Telescope, we report the existence of transient radio pulsations from the direction of LS I +61 degrees 303 with a period P = 269.15508 +/- 0.00016 ms at a significance of >20 sigma. These pulsations strongly argue for the existence of a rotating neutron star within LS I +61 degrees 303.

Automated summary

LS I +61 degrees 303 is one of the rare gamma-ray binaries that emit most of their luminosity in photons with energies beyond 100 MeV. This study reports the existence of transient radio pulsations from LS I +61 degrees 303, providing strong evidence for the presence of a rotating neutron star within the binary.