Basic assumptions in the standard afterglow model O A spherical, ultrarelativistic fireball is ejected 2 The total energy of the shocks is released impulsively before their formation 3 The unshocked medium is homogeneous, and its density is of the order of 1 cm-3 a The electron and magnetic energy-density fractions of the shocked medium and the index p of the electron power-law distribution are constant 6 The emission mechanism is synchrotron radiationBasic assumptions in the standard afterglow model ① A spherical, ultrarelativistic fireball is ejected; ② The total energy of the shocks is released impulsively before their formation; ③ The unshocked medium is homogeneous, and its density is of the order of 1 cm-3 ; ④ The electron and magnetic energy-density fractions of the shocked medium and the index p of the electron power-law distribution are constant; ⑤ The emission mechanism is synchrotron radiation