title: A giant gamma-ray flare from the magnetar SGR 1806-20.
abstract: Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). 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 x 10(46) erg, 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 gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA. palmer@lanl.gov
authors.forename: D M
authors.initials: DM
authors.lastname: Palmer
authors.forename: S
authors.initials: S
authors.lastname: Barthelmy
authors.forename: N
authors.initials: N
authors.lastname: Gehrels
authors.forename: R M
authors.initials: RM
authors.lastname: Kippen
authors.forename: T
authors.initials: T
authors.lastname: Cayton
authors.forename: C
authors.initials: C
authors.lastname: Kouveliotou
authors.forename: D
authors.initials: D
authors.lastname: Eichler
authors.forename: R A M J
authors.initials: RA
authors.lastname: Wijers
authors.forename: P M
authors.initials: PM
authors.lastname: Woods
authors.forename: J
authors.initials: J
authors.lastname: Granot
authors.forename: Y E
authors.initials: YE
authors.lastname: Lyubarsky
authors.forename: E
authors.initials: E
authors.lastname: Ramirez-Ruiz
authors.forename: L
authors.initials: L
authors.lastname: Barbier
authors.forename: M
authors.initials: M
authors.lastname: Chester
authors.forename: J
authors.initials: J
authors.lastname: Cummings
authors.forename: E E
authors.initials: EE
authors.lastname: Fenimore
authors.forename: M H
authors.initials: MH
authors.lastname: Finger
authors.forename: B M
authors.initials: BM
authors.lastname: Gaensler
authors.forename: D
authors.initials: D
authors.lastname: Hullinger
authors.forename: H
authors.initials: H
authors.lastname: Krimm
authors.forename: C B
authors.initials: CB
authors.lastname: Markwardt
authors.forename: J A
authors.initials: JA
authors.lastname: Nousek
authors.forename: A
authors.initials: A
authors.lastname: Parsons
authors.forename: S
authors.initials: S
authors.lastname: Patel
authors.forename: T
authors.initials: T
authors.lastname: Sakamoto
authors.forename: G
authors.initials: G
authors.lastname: Sato
authors.forename: M
authors.initials: M
authors.lastname: Suzuki
authors.forename: J
authors.initials: J
authors.lastname: Tueller