SGR J1550–5418Â ( previously known as AXP 1E 1547.0–5408Â 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 - 1000Â keV ) revealed \sim 450 bursts emitted over 24 hours during the peak of this activity .
Using the GBM data , we identified a \sim 150-s-long enhanced persistent emission during 2009 January 22 that exhibited intriguing timing and spectral properties : ( i ) clear pulsations up to \sim 110Â keV at the spin period of the neutron star ( P \sim 2.07 Â s , the fastest of all magnetars ) , ( ii ) an additional ( to a power-law ) blackbody component required for the enhanced emission spectra with kT \sim 17 Â keV , ( iii ) pulsed fraction that is strongly energy dependent and highest in the 50 - 74Â keV energy band .
A total isotropic-equivalent energy emitted during this enhanced emission is estimated to be 2.9 \times 10 ^ { 40 } ( D / 5 { kpc } ) ^ { 2 } Â erg .
The estimated area of the blackbody emitting region of \approx 0.046 ( D / 5 { kpc } ) ^ { 2 } { km } ^ { 2 } ( roughly a few \times 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 .