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We report the timing and spectral properties of Be/X-ray binary pulsar GX304-1 by using two Suzaku observations during its 2010 August and 2012 JanuaryX-ray outbursts. Pulsations at ~275 s were clearly detected in the light curvesfrom both the observations. Pulse profiles were found to be stronglyenergy-dependent. During 2010 observation, prominent dips seen in soft X-ray($\leq$10 keV) pulse profiles were found to be absent at higher energies.However, during 2012 observation, the pulse profiles were complex due to thepresence of several dips. Significant changes in the shape of the pulseprofiles were detected at high energies ($>$35 keV). A phase shift of $\sim$0.3was detected while comparing the phase of main dip in pulse profiles below andabove $\sim$35 keV. Broad-band energy spectrum of pulsar was well described bya partially absorbed Negative and Positive power-law with Exponential cutoff(NPEX) model with 6.4 keV iron line and a cyclotron absorption feature. Energyof cyclotron absorption line was found to be $\sim$53 and 50 keV for 2010 and2012 observations, respectively, indicating a marginal positive dependence onsource luminosity. Based on the results obtained from phase-resolvedspectroscopy, the absorption dips in the pulse profiles can be interpreted asdue to the presence of additional matter at same phases. Observed positivecorrelation between cyclotron line energy and luminosity, and significantpulse-phase variation of cyclotron parameters are discussed in the perspectiveof theoretical models on cyclotron absorption line in X-ray pulsars.

Suzaku view of Be/X-ray binary pulsar GX 304-1 during Type I X-ray outbursts