Type-I burst detected during its 2015 outburst. The burst start time is 57 228.0926 MJD. The upper panel shows the BAT light curve in the 15–25 keV energy range with a time bin of 2 s (1 s for the inset). The XRT light curve in the bottom panel shows that the narrow field instrument on-board Swift starts to observe the source ~135 s after the onset of the event. The dashed line in this panel indicates the emission level of the X-ray background as measured ~400 s after the burst. The burst is very energetic during the first ~20 s with the tail of the blackbody detected above 25 keV.