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.

The nature of the late achromatic bump in GRB 120326A

GUIDORZI, Cristiano;
2014

Abstract

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.
2014
A., Melandri; F. J., Virgili; Guidorzi, Cristiano; M. G., Bernardini; S., Kobayashi; C. G., Mundell; A., Gomboc; B., Dintinjana; V. P., Hentunen; J., Japelj; D., Kopač; D., Kuroda; A. N., Morgan; I. A., Steele; U., Quadri; G., Arici; D., Arnold; R., Girelli; H., Hanayama; N., Kawai; H., Mikuž; M., Nissinen; T., Salmi; R. J., Smith; L., Strabla; M., Tonincelli; A., Quadri
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/2257814
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