GRB 110721A was detected by the Gamma-ray Burst Monitor and the Large Area Telescope ( LAT ) onboard the Fermi satellite and the Gamma-ray Burst Polarimeter onboard the IKAROS solar mission .
Previous analysis done of this burst showed : i ) a linear polarization signal with position angle stable ( \phi _ { p } = 160 ^ { \circ } \pm 11 ) and high degree of \Pi = 84 ^ { +16 } _ { -28 } % , ii ) an extreme peak energy of a record-breaking at 15 \pm 2 MeV , and iii ) a subdominant prompt thermal component observed right after the onset of this burst .
In this paper , the LAT data around the reported position of GRB 110721A are analysed with the most recent software and then , the LAT light curve above 100 MeV was obtained .
The LAT light curve is modelled in terms of adiabatic early-afterglow external shocks when the outflow propagates into a stellar wind .
Additionally , we discuss the possible origins and also study the implications of the early-afterglow external shocks on the extreme peak energy observed at 15 \pm 2 MeV , the polarization observations and the subdominant prompt thermal component .