2009 Fermi Symposium, Washington, D.C., Nov. 2-5 2 II. INSTRUMENTATION AND DATA III. TEMPORAL PROPERTIES A. Timing Analysis In trigger mode, GBM provides three types of data for each of 12 NaI and 2 BGO detectors; CTIME Burst, CSPEC Burst, and Time Tagged Event (TTE) data [12]. The CTIME Burst data have a time resolu- tion of 64 ms with rather coarse spectral information (8 energy channels). The CSPEC Burst data pro- vide high-resolution spectra (128 energy channels) col- lected every 1.024 s. Both CTIME Burst and CSPEC Burst accumulate data for ∼ 600 s after a trigger. The TTE data provide time-tagged photon event lists for an accumulation time of 330 s, starting 30 s prior to the trigger time; this data type provides a superior temporal resolution down to 2 µ s at the same spectral resolution as the CSPEC Burst data. The first GBM trigger at the onset of the second ac- tive episode from SGR J1550–5418 was on 2009 Jan- uary 22 at 00:53:52.17 UT (= T$_{0}$ , GBM trigger num- ber 090122037). In the 600 s of the trigger readout we detected many individual short bursts using our on-ground untriggered burst search algorithm. To ac- cept an event as an untriggered burst, we required excess count rates of at least 5.5 σ and 4.5 σ in the first and second brightest detectors, respectively, in the 10 − 300 keV energy range. We used CTIME data in both continuous (256 ms time resolution) and Burst mode (64 ms resolution). Subsequently, we inspected energy-resolved burst morphology and compared each detector zenith angle to the source for all 12 detec- tors, to determine whether the events originated from SGR J1550–5418. In total we identified about a dozen very bright bursts and over 40 less intense bursts within 600 s after T$_{0}$ (see Figure 1). During the same trigger readout we also discovered an enhancement in the underlying persistent emission starting at approx- imately T$_{0}$ +70 s and lasting for ∼ 150 s (see inset of Figure 1). In the analysis presented here, we have exclusively used data from NaI 0, which initially had the small- est detector zenith angle to the source (15 $^{◦}$) and to which the source was visible through most of the en- hanced emission. We also note that we checked the LAT data (20 MeV − 300 GeV) of the entire day for as- sociated high-energy gamma-ray emission, but found no evidence of high-energy photons originating from the direction of SGR J1550–5418. During our search for untriggered events in the first trigger interval of 2009 January 22 from SGR J1550–5418, we found strong apparent periodic modulations in the enhanced emission period from T$_{0}$ +130 to 160 s in the 50 − 102 keV data of detector NaI 0 (see panel (c) of Figure 2). This is the first time to our knowledge that pulsations unrelated to a giant flare from a magnetar were clearly seen in the persis- tent emission of an SGR, in energies up to 100 keV. To search for a coherent pulse period, we performed a timing analysis over the entire enhancement inter- val. We first eliminated the times of all the bursts found via our untriggered burst search and converted the remaining burst-free intervals to the solar system barycenter. We then generated a Lomb-Scargle peri- odogram [13, 14] over a range of periods from 0.1 s to 10 s using CTIME Burst data in the 50 − 102 keV band. We found a very significant signal with a Lomb power of 72.6 (chance occurrence probability, P$_{c}$ ≃ 10 − $^{16}$) at a period of 2.0699 ± 0.0024 s, which is consistent with the spin period of SGR J1550–5418. Further, to confirm our detection, we also employed the Z 2 m test (with m = 2) [15] on the burst-free and barycentered TTE data. We find a coherent signal (with a Z 2 m =2 power of 266, P$_{c}$ ≃ 10 − $^{23}$) at the same period. Our spin period measurement is consistent with the one found for SGR J1550–5418 using con- temporaneous X-ray data ( Swift /XRT) [16, 17] and radio data [18]. Therefore, we clearly confirm with the detection of these hard X-ray pulsations that the enhanced persistent emission seen in the inset of Fig- ure 1 originates from SGR J1550–5418. Next we searched in the enhanced persistent emis- sion for evolution in the intensity of the pulsations using a sliding boxcar technique. We found that the pulsed signal peaks over a 90 s interval, from T$_{0}$ +120 to 210 s, which encompasses the peak of the enhance- FIG. 1: GBM lightcurve of SGR J1550–5418 in 12 − 293 keV. An enlarged view of the pulsed, enhanced emission is shown in the inset. The dashed line indicates the background level. eConf C091122