A Comprehensive Analysis of Fermi Gamma-ray Burst Data: II. $E_{\rm p}$-Evolution Patterns and Implications for the Observed Spectrum-Luminosity Relations

Understand

We present a time-resolved spectral analysis of 51 long and 11 short bright GRBs observed with the {\em Femri}/GBM, paying special attention to $E_{\rm p}$ evolution within a same burst.

• Among 8 single-pulse long GRBs, 5 show hard-to-soft evolution, while 3 show intensity-tracking.
• The multi-pulse long GRBs have more complicated patterns.
• Among the GRBs whose time-resolved spectrum is available for the first pulse, almost half (15/32 GRBs) show clear hard-to-soft evolution, and the other half (17/32 GRBs) show clear intensity-tracking.