A giant γ-ray flare from the magnetar SGR 1806−20

Palmer, D. M.
Barthelmy, S.
Gehrels, N.
Kippen, R. M.
Cayton, T.
Kouveliotou, C.
Eichler, D.
Wijers, R. A. M. J.
Woods, P. M.
Granot, J.
Lyubarsky, Y. E.
Ramirez-Ruiz, E.
Barbier, L.
Chester, M.
Cummings, J.
Fenimore, E. E.
Finger, M. H.
Gaensler, B. M.
Hullinger, D.
Krimm, H.
Markwardt, C. B.
Nousek, J. A.
Parsons, A.
Patel, S.
Sakamoto, T.
Sato, G.
Suzuki, M.
Tueller, J.

¹Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
²NASA/Goddard Space Flight Center, and ³Universities Space Research Association, Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
⁴NASA/Marshall Space Flight Center, and ⁵Universities Space Research Association, NSSTC, XD-12, 320 Sparkman Dr., Huntsville, Alabama 35805, USA
⁶Department of Physics, Ben Gurion University, POB 653, Beer Sheva 84105, Israel
⁷Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ, Amsterdam, the Netherlands
⁸Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, PO Box 20450, MS 29, Stanford, California 94309, USA
⁹Institute for Advanced Study, Einstein Drive, Princeton, New Jersey 08540, USA
¹⁰Pennsylvania State University, University Park, Pennsylvania 16802, USA
¹¹National Research Council, 500 Fifth St., NW Washington, DC, 20001, USA
¹²Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS-6, Cambridge, Massachusetts 02138, USA
¹³University of Maryland, College Park, Maryland 20742, USA
¹⁴Institute of Space and Astronautical Science (ISAS)/JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
¹⁵Saitama University, 55 Shimo-Okubo, Sakura-ku, Saitama City, Saitama 338-8570, Japan

Received 2 February; accepted 8 March 2005; doi:10.1038/nature03525.

Supplementary Information accompanies the paper on www.nature.com/nature.

Correspondence and requests for materials should be addressed to D.M.P. ([email protected]).

Nature 434(7037):p 1107-1109, April 28, 2005.

Two classes of rotating neutron stars-soft γ-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B ≈ 10¹⁵G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806−20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 × 10⁴⁶erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard γ-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.