Spectra of various NH₃ inversion transitions integrated over the compact core only of NGC 7538 IRS1. Spectral profiles for transitions (6, 6), (7, 7), (9, 9), (10, 10), (12, 12), (13, 13), and (14, 14) are shown in the same panel, where an offset in flux density of 0.02 Jy is applied to transitions adjacent in energy, to better display individual profiles. The lower state energy levels of transitions shown here are ~ 408−1947 K (see Table 1). The velocity resolution is 0.4 km s^-1. Upper panel: The hyperfine satellite lines, separated by ~ ± 24−31 km s^-1 (see Table 3), are clearly detected for the (6, 6), (7, 7), and (9, 9) lines. Lower panel: A narrower velocity range is displayed here, in order to show more clearly the line profiles of the main hyperfine component of each inversion transition. The vertical dashed lines indicate the two main velocity components at −59.3 km s^-1 and 56.4 km s^-1 (see text).