(a) Schematic illustration of the two distinct zones: the magnetized structure hosting the GRB at redshift z = 0.151 and the surrounding void region. We adopt a comoving size of d_c ∼ 10 Mpc for the structured region, while the weakly magnetized void IGM extends over d_c ∼ 638 Mpc. (b) The observer sphere (R_obs = 638 Mpc) is centered at O, used to record cascade γ rays produced after charged particles (p, e^±) are deflected within the magnetized structure. Events arriving within an aperture angle ∠POS are collected. In this analysis, we apply a narrow angular cut defined by the yellow cone, with half-opening angle ∠TOS = 1° about the line of sight OS. The photon deflection angle is defined as the angle between the photon momentum vector ﹩\hat{{\boldsymbol{n}}}﹩ (e.g., ﹩{\boldsymbol{Q}}{{\boldsymbol{Q}}}^{{\boldsymbol{{\prime} }}}﹩) and the initial jet emission axis, ﹩{\boldsymbol{S}}{\boldsymbol{O}}﹩, taken to be ﹩\hat{{\bf{e}}}=(-1,0,0)﹩. For a statistically significant event sample, the distribution around the line of sight may be regarded as azimuthally symmetric.