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A time-resolved spectral analysis for a sample of 22 intense, broad GRBpulses from the BATSE GRB sample is presented. We fit the spectra with the Bandfunction and investigate the correlation between the observed flux (F) and thepeak energy (E_p) of the $\nu f_\nu$ spectrum in the rising and decaying phasesof these pulses. Two kinds of E_p evolution trends, i.e., hard-to-soft (thetwo-third pulses in our sample) and $E_{\rm p}$-tracing-$F$ (the one-thirdpulses in our sample) are observed in pulses from different GRBs and even fromdifferent pulses of the same burst. No dependence of spectral evolution featureon the pulse shape is found. A tight $F-E_{\rm p}$ positive correlation isobserved in the decaying phases, with a power-law index $\sim 2.2$, which ismuch shallower than that expectation of the curvature effect. In the risingphase, the observed $F$ is either correlated or anti-correlated with $E_{\rmp}$, depending on the spectral evolution feature, and the power-law index ofthe correlation is dramatically different among pulses. More than $80%$ of thelow energy photon indices in the time-resolved spectra whose $E_{\rm p}$ isanti-correlated with $F$ during the rising phase violate the death line of thesynchrotron radiation, disfavoring the synchrotron radiation model for thesegamma-rays. The $F-E_{\rm p}$ correlation, especially for those GRBs with$E_{\rm p}$-tracking-$F$ spectral evolution, may be due to the viewing angleand jet structure effects. In this cenario, the observed $F-E_{\rm p}$correlation in the rising phase may be due to the line of sight from off-beamto on-beam toward a structured jet (or jitter), and the decaying phase iscontributed by both the on-beam emission and the decayed photons from highlatitude of the GRB fireball,resulting in a shallower slope of the observed$F-E_{\rm p}$ correlation than that predicted by the pure curvature effect.

The $E_{\rm p}$-Flux Correlation in the Rising and Decaying Phases of Gamma-Ray Burst Pulses: Evidence for Viewing Angle Effect?