Time-Evolution of Peak Energy and Luminosity Relation within Pulses for GRB 061007: Probing Fireball Dynamics

We performed a time-resolved spectral analysis of a bright, long gamma-ray burst GRB 061007 using Suzaku/WAM and Swift/BAT. Because of the large effective area of the WAM, we can investigate the time evolution of the spectral peak energy E-peak(t) and the luminosity L-iso(t) with 1-s time resolution, and we find that the time-resolved pulses also satisfy the E-peak-L-iso relation, which was found for the time-averaged spectra of other bursts, suggesting the same physical conditions in each pulse. Furthermore, the initial rising phase of each pulse could be an outlier of this relation with higher E-peak(t) Value by a factor of 2. This difference could Suggest that the fireball radius expands by a factor of 2-4 and / or bulk Lorentz factor of the fireball is decelerated by a factor of similar to 4 during the initial phase, providing a new probe of fireball dynamics in real time