Observer frame pulse duration Δt^obs vs. the pulse occurrence time (peak time – ). Times are given with respect to the trigger time. Prompt emission pulses of Fermi/GBM bursts (from Bhat et al. 2012) are shown with different symbols: purple squares show pulses obtained from the analysis of the GBM/NaI [8 keV–1 MeV] light curves, and red diamonds are pulses from GBM/BGO [200 keV–10 MeV] light curves. Orange points, green asterisks, and cyan crosses show XRF (from Yi et al. 2016, Bernardini et al. 2011 and Chincarini et al. 2010). The bottom right inset shows the chance probability vs. the correlation coefficient for the 16 GRBs out of 32 in the B12 sample with ≥10 pulses.