Top: comparison in flux density scale between the PN and PO spectra as observed using the IRAM 30 m antenna (magenta, Lefloch et al. 2016) and that extracted from the NOEMA map (black) from a circular region equal to the IRAM 30m HPBW. Top: PN N= 2–1 spectra. The HPBW is 26″.2. The vertical dot-dashed line marks the systemic velocity of L1157-mm (V = +2.7 km s⁻¹). The blue lines indicate the frequencies of the ΔJ = 0, ±1 transitions of the N = 2–1 pattern (see Table 1). Middle: same as in the top panel but for the PO ²Π_1/2 J = 5/2–3/2 F = 3–2 f transition (IRAM 30 m beam: 22″.6). Bottom: same as in the middle panel but for the PO transition ²Π_1/2 J = 5/2–3/2 F = 3–2 e.