Extensive multi-band afterglow data are available for GRB 980703. Especially,its radio afterglow was very bright and was monitored until more than 1000 days after the trigger time. Additionally,there is no obvious special feature,i.e.,no rebrightenings,no plateau,and no special steep decay or slow decay in the multi-band afterglow light curves. All these conditions make GRB 980703 a precious sample in gammaray burst research. Here we use the observational data of GRB 980703 to test the standard fireball model in depth. It is found that the model can give a satisfactory explanation to the multi-band and overall afterglow light curves. The beaming angle of GRB 980703 is derived as ～ 0.23 radian,and the circum-burst medium density is ～ 27 cm-3. The total isotropic equivalent kinetic energy of the ejecta is ～ 3.8 × 1052 ergs. A rest-frame extinction of AV ～ 2.5 mag in the host galaxy is also derived.
We investigate in detail the influence of parametrizations of the dark energy equation of state on reconstructing dark energy geometrical parameters,such as the deceleration parameter q(z) and Om diagnostic.We use a type Ia supernova sample,baryon acoustic oscillation data,cosmic microwave background information along with twelve observational Hubble data points to constrain cosmological parameters.With the joint analysis of these current datasets,we find that the parametrizations of w(z) have little influence on the reconstruction result of q(z) and Om.The same is true for the transition(cosmic deceleration to acceleration) redshift zt,for which we find that for different parametrizations of w(z),the best fitted values of zt are very close to each other(about 0.65).All of our results are in good agreement with the ΛCDM model.Furthermore,using the combination of datasets,we do not find any signal of decreasing cosmic acceleration as suggested in some recent papers.The results suggest that the influence of the prior w(z) is not as severe as one may anticipate,and thus we can,to some extent,safely use a reasonable parametrization of w(z) to reconstruct some other dark energy parameters(e.g.q(z),Om) with a combination of datasets.
