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

Abstract

LS I +61° 303 is one of the rare gamma-ray binaries1 that emit most of their luminosity in photons with energies beyond 100 MeV (ref. 2). It is well characterized—the ~26.5 day orbital period is clearly detected at many wavelengths2,3,4—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 component5 and LS I +61° 303 also shows superorbital variability3,6,7,8,9. A couple of energetic (~1037 erg s−1), short, magnetar-like bursts have been plausibly ascribed to it10,11,12,13. Although the phenomenology of LS I +61° 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° 303 with a period P = 269.15508 ± 0.00016 ms at a significance of >20σ. These pulsations strongly argue for the existence of a rotating neutron star within LS I +61° 303.

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Fig. 1: Radio pulsations were recorded in the FAST data recorded on 2020 January 7.

Data availability

The datasets generated during and/or analysed during the current study are available from the corresponding authors on reasonable request.

Code availability

PRESTO is available at https://www.cv.nrao.edu/~sransom/presto/ and BEAR is available at https://psr.pku.edu.cn/index.php/publications/software.

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Acknowledgements

This work made use of the data from FAST. FAST is a Chinese national mega-science facility, operated by National Astronomical Observatories, Chinese Academy of Sciences. We acknowledge the use of the ATNF Pulsar Catalogue. S.-S.W. and B.-J.W. thank Z. Pan for discussions on the FAST data analysis. S.-S.W. thanks Z.-X. Wang, S.-N. Zhang and K. Lee for many valuable discussions. J.L., D.F.T. and A.P. acknowledge discussions with the international team on ‘Understanding and unifying the gamma rays emitting scenarios in high mass and low mass X-ray binaries’ of the ISSI (International Space Science Institute), Beijing. We acknowledge support from National Key R&D programme of China grant numbers 2017YFA0402602 and 2021YFA0718500, National SKA Program of China grant numbers 2020SKA0120100 and 2020SKA0120201, National Natural Science Foundation of China grant numbers U2038103, 11733009, U2031205, U1938109 and 11873032, the Youth Innovation Promotion Association of the CAS (grant id 2018075), the Chinese Academy of Sciences Presidential Fellowship Initiative 2021VMA0001, National Foreign Experts Program of Ministry of Science and Technology of the People’s Republic of China grant number G2021200001L and the International Visiting Professorship programme of the University of Science and Technology of China grant number 2021BVR05. S.-S.W. acknowledges financial support from the Jiangsu Qing Lan Project. D.F.T. also acknowledges grants PID2021-124581OB-I00, PGC2018-095512-B-I00 and Spanish programme Unidad de Excelencia ‘María de Maeztu’ grant number CEX2020-001058-M. A.P. acknowledges financial support from the Italian Space Agency (ASI) and National Institute for Astrophysics (INAF) under grant agreement numbers ASI-INAF I/037/12/0 and ASI-INAF n.2017-14-H.0, from INAF ’Sostegno alla ricerca scientifica main streams dell’INAF’, Presidential Decree 43/2018 and from PHAROS COST Action number 16214.

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S.-S.W. proposed the observational project. The FAST team led by P.J. designed and scheduled the observations during the FAST commissioning stage. L.Q. carried out the observations and B.J-.W. analysed the data. D.F.T., J.L. and A.P. contributed to interpreting the results. D.F.T., S.-S.W. and B.-J.W. wrote the paper. P.J., R.X., J.-Z.Y., Q.-Z.L., M.-Y.G. and Q.-R.Y. participated in the interpretation of the results. All authors discussed the contents of the paper and contributed to the preparation of the manuscript.

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Correspondence to Shan-Shan Weng or D. F. Torres.

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Nature Astronomy thanks Jumpei Takata, Scott Ransom and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Weng, SS., Qian, L., Wang, BJ. et al. Radio pulsations from a neutron star within the gamma-ray binary LS I +61° 303. Nat Astron 6, 698–702 (2022). https://doi.org/10.1038/s41550-022-01630-1

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