Soft γ-ray repeaters (SGRs) are ‘magnetars’, a small class of slowly spinning neutron stars with extreme surface magnetic fields, B ≈ 1015 gauss (refs 1, 2–3). On 27 December 2004, a giant flare4 was detected from the magnetar SGR 1806 - 20 (ref. 2), only the third such event recorded5,6. This burst of energy was detected by a variety of instruments7,8 and even caused an ionospheric disturbance in the Earth's upper atmosphere that was recorded around the globe9. Here we report the detection of a fading radio afterglow produced by this outburst, with a luminosity 500 times larger than the only other detection of a similar source10. From day 6 to day 19 after the flare from SGR 1806 - 20, a resolved, linearly polarized, radio nebula was seen, expanding at approximately a quarter of the speed of light. To create this nebula, at least 4 × 1043 ergs of energy must have been emitted by the giant flare in the form of magnetic fields and relativistic particles.
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We thank J. Ulvestad, J. Wrobel, R. Sault, A. Foley and R. Vermeulen for rapid scheduling of the VLA, ATCA and WSRT; T. DeLaney, G. de Bruyn and C. Brogan for assistance with data analysis; and R. Manchester, D. Frail and M. Wieringa for help with the observations. NRAO is a facility of the NSF operated under cooperative agreement by AUI. The Australia Telescope is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. The MOST is operated by the University of Sydney and supported in part by grants from the ARC. The WSRT is operated by ASTRON with financial support from NWO. B.M.G. acknowledges the support of NASA through a Long Term Space Astrophysics grant. D. E. acknowledges support from the Israel–US BSF, the ISF and the Arnow Chair of Physics. Y.E.L. acknowledges support from the German-Israeli Foundation. R.A.M.J.W. and A.J.H. acknowledge support from NWO.
The authors declare that they have no competing financial interests.
This table lists the flux density of the transient radio source coincident with SGR 1806-20 as a function of both time and frequency. The techniques used to make these flux density measurements are also described. (PDF 26 kb)
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Gaensler, B., Kouveliotou, C., Gelfand, J. et al. An expanding radio nebula produced by a giant flare from the magnetar SGR 1806–20. Nature 434, 1104–1106 (2005). https://doi.org/10.1038/nature03498
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