To identify extragalactic magnetar flares , we have searched for their periodic tails by generating Lomb periodograms of the emission following short bursts detected by the Burst and Transient Source Experiment ( BATSE ) .
Out of 358 short bursts examined , one has a significant tail periodicity ( T = 13.8 s , { P = 4 \times 10 } ^ { -5 } ) .
The most probable host galaxy for this burst is “ The Fireworks Galaxy ” NGC 6946 ( d = 5.9 Mpc ) .
At this distance , the energy of the spike , { ( 2.7 \pm 0.3 ) \times 10 } ^ { 44 } ergs , is akin to those of the galactic magnetar giant flares , as are its duration ( \sim 0.4 s ) and temperature ( 250 \pm 60 keV ) .
For the tail emission , however , our estimated temperature of 60 \pm 5 keV is harder and the energy release of { ( 4.3 \pm 0.8 ) \times 10 } ^ { 45 } ergs is larger than those of the galactic magnetar flares .
Regardless of the host , such a large ratio of tail-to-spike energy would imply that magnetar flare tails might be detectable out to further distances than previously thought .