The long Swift gamma-ray burst GRB120326A at redshift z = 1.798 exhibited a multi-band light-curve with a striking feature: a latetime,
long-lasting achromatic rebrightening that is rarely seen in such events. Peaking in optical and X-ray bands ~35 ks (~12.5 ks in the GRB rest frame) after the 70 s GRB prompt burst, the feature brightened nearly two orders of magnitude above the underlying
optical power-law decay. By modelling the multi-wavelength light-curves, we investigated possible causes of the rebrightening in the
context of the standard fireball model. We excluded a range of scenarios for the origin of this feature: reverse-shock flash, late-time
forward-shock peak caused by the passage of the brightest synchrotron frequency through the optical band, late central engine optical or X-ray flares, interaction between the expanding blast wave and a density enhancement in the circumburst medium, and gravitational microlensing. Instead we conclude that the achromatic rebrightening may be caused by a refreshed forward shock or a geometrical effect. In addition, we identify an additional component after the end of the prompt emission, which shapes the observed X-ray and optical light-curves differently, and which rules out a single overall emission component to explain the observed early-time emission
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