A Magnetar Flare in the BATSE Catalog?

Abstract

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 x 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 +/- 0.3) x 10^44 ergs, is akin to those of the galactic magnetar giant flares, as are its duration (~ 0.4 s) and temperature (250 +/- 60 keV). For the tail emission, however, our estimated temperature of 60 +/- 5 keV is harder and the energy release of (4.3 +/- 0.8) x 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.