6 2009 Fermi Symposium, Washington, D.C., Nov. 2-5 0 . 046 D 2 5 km $^{2}$, where T ≈ 2 × 10 8 $^{◦}$K ( kT ≈ 17 keV) is the observed (gravitationally redshifted) tempera- ture. We have used here the blackbody flux at the peak of the pulsations (i.e., phase maximum; F ≈ 5 × 10 − 8 erg cm − 2 s − $^{1}$) where the hot-spot is expected to be relatively close to face-on, in order to minimize the effects of projection and gravitational lensing by the neutron star, so that S ∞ would be relatively close to the physical area, S , of the hot spot on the neutron star surface. For a circular hot-spot, this corresponds to a radius of ∼ 120 D$_{5}$ m. The internal field of magnetars can be significantly stronger and more tangled than the external dipole field. As the internal field twists the stellar crust, the magnetosphere also becomes twisted, possibly in a complex manner [24]. If we identify the inferred size of the hot-spot as the size of a twisted region on the stellar surface, the rate of energy dissipation is expected to be L$_{d}$ ≪ 10 38 erg s − 1 for global stabil- ity case [25]. This is inconsistent with the observed luminosity of the spot, L$_{d}$ ∼ 10 $^{38}$D 2 5 erg s − 1 It may be possible for the magnetic twist to grow to a global instability level during a highly active bursting period due to frequent starquakes [25]. As the magnetosphere untwists, a large amount of en- ergy must be dissipated [26]. A small “trapped fire- ball” – plasma of e ± pairs and photons confined by a closed magnetic field region – could then poten- tially account for the inferred hot-spot, and in partic- ular its roughly constant temperature and size. Con- fining a “fireball” of energy at least comparable to that emitted by the observed blackbody component, E$_{iso}$$_{,}$$_{BB}$ ≈ 5 . 6 × 10 $^{39}$D 2 5 erg, within a region of radius a ∼ 120 D$_{5}$ m requires E$_{B}$ ( a ) = 1 $_{6}$a$^{3}$B 2 > E$_{iso}$$_{,}$$_{BB}$ or B > ∼ 1 . 4 × 10 $^{14}$D − 1 / 2 5 G. This is consistent with the surface dipole field of B ≈ 2 . 2 × 10 14 G inferred from the measured P ˙ P [3]. Therefore, a sufficiently small closed magnetic loop anchored by the crust could pro- vide the required confinement. Moreover, the black- body emission is expected to be accompanied by non- thermal, high-energy radiation produced by collision- less dissipation, with the luminosities comparable to the blackbody components [25]. This is in good agree- ment with our observations of SGR J1550–5418. In conclusion, the area of the blackbody emitting region observed here is the smallest “hot spot” mea- sured for a magnetar, which likely arises from magnet- ically confined hot plasma on the neutron star surface, possibly caused by the gradual dissipative untwisting of the magnetosphere [26]. If the total radiated en- ergy was initially confined to the inferred extremely small size of the enhanced emission region (as in a mini “trapped fireball” scenario), this would indicate a very large magnetic energy density, similar to the “trapped fireball” model for the tails of SGR giant flares. The observed enhanced emission that we report here is much less energetic than a giant flare tail, while its energy is comparable to the tail energy of interme- diate events and at the high end of typical SGR bursts. Despite some distinct properties, the enhanced emis- sion of SGR J1550–5418 carries various flavors of all three SGR phenomena, and thus it is most likely re- lated to the very pronounced bursting activity that immediately followed it. This publication is part of the GBM/Magnetar Key Project (NASA grant NNH07ZDA001-GLAST, PI: C. Kouveliotou). We thank G.L. Israel and A. Tiengo for providing the precise spin ephemeris and source distance, respectively, prior to their publication. YK and EG acknowledge EU FP6 Transfer of Knowledge Project “Astrophysics of Neutron Stars” (MTKD-CT- 2006-042722). EG acknowledges partial support from Turkish Academy of Sciences. JG gratefully acknowl- edges a Royal Society Wolfson Research Merit Award. ER-R thanks the Packard Foundation for support. 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