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arXiv · 0911.4636

Magnetar Twists: Fermi/Gamma ray Burst Monitor (GBM) detection of SGR J1550-5418

Y. Kaneko·E. Gogus·C. Kouveliotou·J. Granot·E. Ramirez-Ruiz·A. J. van der Horst·A. L. Watts·M. H. Finger·N. Gehrels·A. Pe'er·M. van der Klis·A. von Kienlin·S. Wachter·C. A. Wilson-Hodge·P. M. Woods
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Abstract

SGR J1550-5418 (previously known as AXP 1E 1547.0-5408 or PSR J1550-5418) went into three active bursting episodes in 2008 October and in 2009 January and March, emitting hundreds of typical Soft Gamma Repeater (SGR) bursts in soft gamma-rays. The second episode was especially intense, and our untriggered burst search on Fermi/GBM data (8-1000 keV) revealed ~450 bursts emitted over 24 hours 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: (i) clear pulsations up to ~110 keV at the spin period of the neutron star (P ~ 2.07 s, the fastest of all magnetars), (ii) an additional (to a power-law) blackbody component required for the enhanced emission spectra with kT ~ 17 keV, (iii) 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 x 10^{40} (D/5 kpc)^2 erg. The estimated area of the blackbody emitting region of ~0.046(D/5 kpc)^2 km^2 (roughly a few x 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.

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Y. Kaneko, E. Gogus, C. Kouveliotou, J. Granot, E. Ramirez-Ruiz, A. J. van der Horst, A. L. Watts, M. H. Finger, N. Gehrels, A. Pe'er, M. van der Klis, A. von Kienlin, S. Wachter, C. A. Wilson-Hodge, P. M. Woods. 2009-12-16. Magnetar Twists: Fermi/Gamma ray Burst Monitor (GBM) detection of SGR J1550-5418. https://doi.org/10.1088/0004-637x%2F710%2F2%2F1335%2010.1088%2F0004-637x%2F712%2F1%2F761

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