Swings between rotation and accretion power in a binary millisecond pulsar


It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods1,2,3. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar4,5 whose emission is powered by the neutron star’s rotating magnetic field6. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars7,8 and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar9. It has been proposed that a rotation-powered pulsar may temporarily switch on10,11,12 during periods of low mass inflow13 in some such systems. Only indirect evidence for this transition has hitherto been observed14,15,16,17,18. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

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Figure 1: Variability of the X-ray emission of IGR J18245–2452.
Figure 2: Spin and orbit of IGR J18245–2452.
Figure 3: Long-term X-ray variability of IGR J18245–2452.


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This letter is based on ToO observations made with XMM-Newton, Chandra, INTEGRAL, Swift, ATCA, WSRT, GBT and PKS. We thank the respective directors and operation teams for their support. Work was done in the framework of grants AYA2012-39303, SGR2009-811 and iLINK2011-0303, and with the support of CEA/Irfu, IN2P3/CNRS and CNES (France), INAF (Italy), NWO (The Netherlands) and NSERC (Canada). A.Pa. is supported by a Juan de la Cierva Research Fellowship. A.R. acknowledges Sardinia Regional Government for financial support (P.O.R. Sardegna ESF 2007-13). D.F.T. was additionally supported by a Friedrich Wilhelm Bessel Award of the Alexander von Humboldt Foundation. L.P. thanks the Société Académique de Genève and the Swiss Society for Astrophysics and Astronomy. We acknowledge the use of data supplied by the UK Swift Science Data Centre at the University of Leicester. A.Pa. thanks S. Giannetti, D. Lai, R. V. E. Lovelace, M. M. Romanova and T. Tauris for discussions, and S. D. Wolf for operational support.

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A.Pa., C.F. and E.B. collected and analysed XMM-Newton data. A.Pa. and C.F. detected the pulsar in XMM-Newton data and derived its orbital solution. A.Pa. discovered the equivalence of its parameters with a radio pulsar, the thermonuclear burst and the burst oscillations. N.R. analysed Chandra data, detecting the X-ray quiescent counterpart of the source and past accretion events. L.P., M.H.W., M.D.F. and G.F.W. analysed ATCA data. E.B., S.C., P.R., A.Pa. and A.R. analysed Swift data. E.B. and C.F. analysed INTEGRAL data. J.W.T.H. analysed WSRT data. M.B. and J.M.S. analysed PKS data. J.W.T.H., S.M.R., A.Po., I.H.S. and P.C.C.F. analysed GBT data. A.R. provided software tools. A.Pa., N.R. and J.W.T.H. wrote the manuscript, with significant contribution by all the authors in interpreting the results and editing of the manuscript.

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Correspondence to A. Papitto.

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Papitto, A., Ferrigno, C., Bozzo, E. et al. Swings between rotation and accretion power in a binary millisecond pulsar. Nature 501, 517–520 (2013). https://doi.org/10.1038/nature12470

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