Magnetar twists: Fermi/gamma-ray burst monitor detection of SGRJ1550-5418

Yuki Kaneko, Ersin Göü, Chryssa Kouveliotou, Jonathan Granot, Enrico Ramirez-Ruiz, Alexander J. Van Der Horst, Anna L. Watts, Mark H. Finger, Neil Gehrels, Asaf Pe'Er, Michiels Van Der Klis, Andreas Von Kienlin, Stefanie Wachter, Colleen A. Wilson-Hodge, Peter M. Woods

Research output: Contribution to journalArticlepeer-review


SGRJ1550-5418 (previously known as AXP1E1547.0-5408 or PSRJ1550-5418) went into three active bursting episodes in 2008 October and in 2009 January and March, emitting hundreds of typical soft gamma repeater bursts in soft gamma rays. The second episode was especially intense, and our untriggered burst search on Fermi/Gamma-ray Burst Monitor (GBM) data (8-1000 keV) revealed 450 bursts emitted over 24 hr during the peak of this activity. Using the GBM data, we identified a 150 s long enhanced persistent emission during 2009 January 22 that exhibited intriguing timing and spectral properties: (1) clear pulsations up to 110 keV at the spin period of the neutron star (P 2.07 s, the fastest of all magnetars); (2) an additional (to a power-law) blackbody component required for the enhanced emission spectra with kT 17 keV; and (3) pulsed fraction that is strongly energy dependent and highest in the 50-74 keV energy band. A total isotropic-equivalent energy emitted during this enhanced emission is estimated to be 2.9 × 1040(D/5 kpc)2 erg. The estimated area of the blackbody emitting region of 0.046(D/5 kpc)2 km2 (roughly a few ×10-5 of the neutron star area) is the smallest "hot spot" ever measured for a magnetar and most likely corresponds to the size of magnetically confined plasma near the neutron star surface.

Original languageEnglish
Pages (from-to)1335-1342
Number of pages8
JournalAstrophysical Journal
Issue number2
StatePublished - 2010
Externally publishedYes


  • Pulsars: individual (SGR J1550?5418, 1E 1547.0?5408, PSR J1550-5418)
  • Stars: neutron
  • X-rays: bursts


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