  The bright, short and hard GRB 090510 was detected by all instruments aboard
Fermi and Swift satellites. The multiwavelength observations of this burst
presented similar features with the Fermi-LAT-detected gamma-ray bursts. In the
framework of the external shock model of early afterglow, a leptonic scenario
that evolves in a homogeneous medium is proposed to revisit GRB 090510 and
explain the multiwavelength light curve observations presented in this burst.
These observations are consistent with the evolution of a jet before and after
the jet break. The long-lasting LAT, X-ray and optical fluxes are explained in
the synchrotron emission from the adiabatic forward shock. Synchrotron
self-Compton emission from the reverse shock is consistent with the bright LAT
peak provided that progenitor environment is entrained with strong magnetic
fields. It could provide compelling evidence of magnetic field amplification in
the neutron star merger.
