1. UC Berkeley Space Sciences Laboratory, Berkeley, California 94720-7450, USA
2. University of California, Department of Physics, Berkeley, California 94720, USA
3. Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, California 95064, USA
4. University of Texas, Department of Astronomy, Austin, Texas 78712, USA
5. Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
6. Canadian Institute of Theoretical Astrophysics, 60 St George Street, Toronto, Ontario M5S 3H8, Canada
7. Space Research Institute (IKI), GSP7, Moscow 117997, Russia
8. University of Arizona, Department of Planetary Sciences, Tucson, Arizona 85721, USA
9. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse (Postfach 1312), 85748 (85741) Garching, Germany
10.  NASA Goddard Space Flight Center, Code 661, Greenbelt, Maryland 20771, USA

Correspondence to: K. Hurley¹ Correspondence and requests for materials should be addressed to K.H. (Email: khurley@ssl.berkeley.edu).

Abstract

Soft--ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806–20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic -ray burst. At least a significant fraction of the mysterious short-duration -ray bursts may therefore come from extragalactic magnetars.

1. UC Berkeley Space Sciences Laboratory, Berkeley, California 94720-7450, USA
2. University of California, Department of Physics, Berkeley, California 94720, USA
3. Physics Department and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, California 95064, USA
4. University of Texas, Department of Astronomy, Austin, Texas 78712, USA
5. Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
6. Canadian Institute of Theoretical Astrophysics, 60 St George Street, Toronto, Ontario M5S 3H8, Canada
7. Space Research Institute (IKI), GSP7, Moscow 117997, Russia
8. University of Arizona, Department of Planetary Sciences, Tucson, Arizona 85721, USA
9. Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse (Postfach 1312), 85748 (85741) Garching, Germany
10.  NASA Goddard Space Flight Center, Code 661, Greenbelt, Maryland 20771, USA

Correspondence to: K. Hurley¹ Correspondence and requests for materials should be addressed to K.H. (Email: khurley@ssl.berkeley.edu).

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