content_image/435309.jpg content_image/435310.jpg
<img src='content_image/435309.jpg'>

ment. Finally, we searched for any other intervals ex- hibiting pulsed emission in the burst-free continuous CTIME data of 2009 January 22 and during the four subsequent days, using a sliding boxcar of 120 s with 10 s steps. We did not find any additional statistically- significant pulsed emission. For the entire search and for all the timing analysis reported here, we used more precise spin ephemeris obtained by contemporaneous Swift /XRT, Chandra, XMM-Newton and Suzaku ob- servations [19]. 

To investigate the evolution of the pulse profiles with energy, we folded the burst-free TTE data span- ning 120 s (from T$_{0}$ +100 s to T$_{0}$ +220 s, which in- cludes the strongest pulsation period as found above) with the spin ephemeris of SGR J1550–5418. We es- timated the background level using the data segment between T$_{0}$ to T$_{0}$ +60 s. Figure 3 shows the source pulse profiles during the enhanced emission interval 

## B. Pulse Profiles 

<img src='content_image/435310.jpg'>

in six energy bands that have the same logarithmic width. The pulse profiles above 110 keV are consis- tent with random fluctuations, and thus not shown. 

Figure 3 indicates that the SGR J1550–5418 pulse profiles in the three lowest energy bands are most likely complex (multi-peaked). While the two low- est energy band profiles are dominated by the struc- ture around phase 0.7-0.8 (indicated by the dotted lines in Figure 3), in the 14 − 22 keV band we see the emergence of another structure around phase 0.0 (in- dicated by the dashed lines in Figure 3). This pulse becomes equally prominent in the 22 − 33 keV range and then dominates in the 33 − 50 keV band. The pulse profile changes remarkably in the 50-74 keV band, which is the most statistically significant of all the energy bands investigated, and is distinguished by a broad structure that peaks at around phase 0.0. The 74 − 110 keV profile resembles the 50-74 keV one. As noted above, the pulse profile above 110 keV is consis- tent with random fluctuations. Therefore, our results set an observed upper energy bound of 110 keV for the hard X-ray pulsations in SGR J1550–5418 during this enhanced emission episode. 

