Addendum to “Coherent radio pulses from GEANT generated electromagnetic showers in ice”

We reevaluate our published calculations of electromagnetic showers generated by GEANT 3.21 and the radio frequency pulses they produce in ice. We are prompted by a recent report showing that GEANT 3.21–modeled showers are sensitive to internal settings in the electron tracking subroutine. We report the shower and pulse characteristics obtained with different settings of GEANT 3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21 we used in previous work speeds up the shower simulation at the cost of information near the end of the tracks. We find that settings tracking [Formula Presented] and [Formula Presented] to lower energy yield a more accurate calculation, a more intense shower, and proportionately stronger radio pulses at low frequencies. The key features of the showers and pulses agree among GEANT 4 and Zas, Halzen, and Stanev and properly set GEANT 3.21 codes. At high frequencies the relation between the shower tracking algorithm and the pulse spectrum is more complex. We obtain radial distributions of shower particles and phase distributions of pulses from 100 GeV showers that are consistent with our published results.