@article{c9b435b5ea934f1aae9aaf60686e6d5b,
title = "A magnetar-powered X-ray transient as the aftermath of a binary neutron-star merger",
abstract = "Mergers of neutron stars are known to be associated with short γ-ray bursts1–4. If the neutron-star equation of state is sufficiently stiff (that is, the pressure increases sharply as the density increases), at least some such mergers will leave behind a supramassive or even a stable neutron star that spins rapidly with a strong magnetic field5–8 (that is, a magnetar). Such a magnetar signature may have been observed in the form of the X-ray plateau that follows up to half of observed short γ-ray bursts9,10. However, it has been expected that some X-ray transients powered by binary neutron-star mergers may not be associated with a short γ-ray burst11,12. A fast X-ray transient (CDF-S XT1) was recently found to be associated with a faint host galaxy, the redshift of which is unknown13. Its X-ray and host-galaxy properties allow several possible explanations including a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at high redshift, or a tidal disruption event involving an intermediate-mass black hole and a white dwarf13. Here we report a second X-ray transient, CDF-S XT2, that is associated with a galaxy at redshift z = 0.738 (ref. 14). The measured light curve is fully consistent with the X-ray transient being powered by a millisecond magnetar. More intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host galaxy with a moderate offset from the galaxy centre, as short γ-ray bursts often do15,16. The estimated event-rate density of similar X-ray transients, when corrected to the local value, is consistent with the event-rate density of binary neutron-star mergers that is robustly inferred from the detection of the gravitational-wave event GW170817.",
author = "Xue, {Y. Q.} and Zheng, {X. C.} and Y. Li and Brandt, {W. N.} and B. Zhang and B. Luo and Zhang, {B. B.} and Bauer, {F. E.} and H. Sun and Lehmer, {B. D.} and Wu, {X. F.} and G. Yang and X. Kong and Li, {J. Y.} and Sun, {M. Y.} and Wang, {J. X.} and F. Vito",
note = "Funding Information: Acknowledgements We thank A. Lien, K. Hurley and D. Svinkin for examining the relevant Swift/BAT, IPN3, and Wind/KNOUS data, respectively, for us. Y.Q.X., X.C.Z., J.Y.L. and M.Y.S. acknowledge support from the 973 Program (2015CB857004), the National Natural Science Foundation of China (grant numbers NSFC-11473026, NSFC-11890693 and NSFC-11421303), the CAS Frontier Science Key Research Program (QYZDJ-SSW-SLH006), the China Scholarship Council (CSC)-Leiden University Joint Scholarship Program, the China Postdoctoral Science Foundation (2016M600485), and the K. C. Wong Education Foundation. Y.L. acknowledges support by the KIAA-CAS Fellowship, which is jointly supported by Peking University and the Chinese Academy of Sciences. W.N.B. and G.Y. acknowledge support from Chandra X-ray Center grant AR8-19016X, NASA grant NNX17AF07G, NASA ADP grant 80NSSC18K0878 and the V. M. Willaman Endowment. B.L. acknowledges support from the National Key R&D Program of China (2016YFA0400702) and NSFC-11673010. B.-B.Z. acknowledges support from the National Thousand Young Talents programme of China and the National Key Research and Development Program of China (2018YFA0404204) and NSFC-11833003. F.E.B. acknowledges support from CONICyT-Chile (Basal AFB-170002, FONDECyT Regular 1141218, FONDO ALMA 31160033) and the Ministry of Economy, Development, and Tourism{\textquoteright}s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics (MAS). F.V. acknowledges financial support from CONICyT and CASSACA through the fourth call for tenders of the CAS-CONICyT fund.",
year = "2019",
month = apr,
day = "11",
doi = "10.1038/s41586-019-1079-5",
language = "English (US)",
volume = "568",
pages = "198--201",
journal = "Nature",
issn = "0028-0836",
publisher = "Nature Publishing Group",
number = "7751",
}