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  • Letter
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Anisotropic winds in a Wolf–Rayet binary identify a potential gamma-ray burst progenitor


The massive evolved Wolf–Rayet stars sometimes occur in colliding-wind binary systems in which dust plumes are formed as a result of the collision of stellar winds1. These structures are known to encode the parameters of the binary orbit and winds2,3,4. Here we report observations of a previously undiscovered Wolf–Rayet system, 2XMM J160050.7–514245, with a spectroscopically determined wind speed of ~3,400 km s−1. In the thermal infrared, the system is adorned with a prominent ~12″ spiral dust plume, revealed by proper motion studies to be expanding at only ~570 km s−1. As the dust and gas appear to be coeval, these observations are inconsistent with existing models of the dynamics of such colliding-wind systems5,6,7. We propose that this contradiction can be resolved if the system is capable of launching extremely anisotropic winds. Near-critical stellar rotation is known to drive such winds8,9, suggesting that this Wolf–Rayet system may be a Galactic progenitor system for long-duration gamma-ray bursts.

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Fig. 1: VISIR 8.9 μm image of Apep taken on 2016 August 13, displaying the exotic dust pattern being sculpted by the system.
Fig. 2: SINFONI J-band and H+K-band spectra for the Central Engine at the centre of the NACO image shown in the inset of Fig. 1.
Fig. 3: The 1.083 μm He i line from the continuum-corrected IRIS2 long-slit Js-band spectrum of Apep.
Fig. 4: A geometric model of the dust plume of Apep.

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Data availability

All data included in this manuscript are now available in the public domain. The VISIR, NACO and SINFONI data are available through the ESO archive. The ATCA data are available through the Australia Telescope Online Archive (ATOA). The IRIS2 data are available through the AAT Data Archive. The X-ray data are available through the XMM-Newton Science Archive (XSA) and Chandra Data Archive.


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J.R.C. thanks B. Gaensler and S. Farrell for conceiving the radio and X-ray survey that led to the discovery of Apep. We also thank N. Smith, K. Valenta and O. de Marco for discussions in the early stages of this study and A. Cheetham for help in constructing the NACO and VISIR observing schedules. We thank R. Lau for reviewing our manuscript and providing insightful comments that lead to important improvements in the manuscript. P.G.T. and B.J.S.P. are grateful for funding from the Breakthrough Prize Foundation. This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. B.J.S.P. is a NASA Sagan Fellow. P.M.W. is grateful to the Institute for Astronomy for continued hospitality and access to the facilities of the Royal Observatory, Edinburgh. We acknowledge the Gadigal clan of the Eora nation, the traditional owners of the land on which the University of Sydney is built, and we pay our respects to their knowledge, and their elders past, present and future. We also thank Y. Han and J. Prenzler. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France, and NASA’s Astrophysics Data System. The results presented in this Letter are based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 097.C-0679(A), 097.C-0679(B), 299.C-5032(A) and 299.C-5032(B). The Australia Telescope Compact Array is part of the Australia Telescope National Facility that is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The scientific results reported in this article are based in part on data acquired through the Australian Astronomical Observatory, on data obtained from the Chandra Data Archive, and observations obtained with XMM-Newton, an European Space Agency (ESA) science mission with instruments and contributions directly funded by ESA Member States and NASA.

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Authors and Affiliations



J.R.C. conducted the survey that identified Apep, wrote the initial draft of the manuscript, conducted and reduced the ATCA observations, and reduced the IRIS2, SINFONI, XMM-Newton and Chandra observations. P.G.T. measured the proper motion of the dust spiral, led the discussion and interpretation of the object, led the VISIR and NACO observing proposals, and contributed significantly to the writing and editing of the manuscript. B.J.S.P. contributed significantly to the understanding and discussion of the object, provided editing and text for the manuscript, and analysed the Gaia and NACO data. P.M.W. interpreted the infrared spectrum, provided the text for the manuscript, produced the infrared/optical photometric SED, measured the equivalent widths of the emission lines, and contributed to the discussion about the object. P.A.C. helped interpret the infrared spectra and critiqued the manuscript. M.E. and B.N. reduced the VISIR and NACO data. L.K.-C. conducted the IRIS2 observation.

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Correspondence to J. R. Callingham.

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Supplementary text, Supplementary Figures 1–5, Supplementary Tables 1–4, Supplementary references

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Callingham, J.R., Tuthill, P.G., Pope, B.J.S. et al. Anisotropic winds in a Wolf–Rayet binary identify a potential gamma-ray burst progenitor. Nat Astron 3, 82–87 (2019).

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