Synchrotron spectra of each representative case. The dashed, dotted–dashed, solid, and dotted lines represent the IC-dominated, eB-dominated, pp-dominated, and nominal cases, respectively. The thick red and thin black lines indicate the cases with E_cut,e = E_cut,p and E_cut,e = 30 TeV, respectively. The circle shows the upper limit taken from W. Reich & X.-H. Sun (2019), while the square shows the upper limit derived in this work.