[Table: Table 3: Fitted Effective Scale Lengths for Pre-perihelion NH2.]

We apply radial Haser profile fitting to dissect the extended production mechanisms of CN and NH2, using methods most recently described in Ferellec et al. (2024). We identified potential contributions from extended sources for NH2, however, maps in other species had insufficient SNR to analyse in this way. First described in Opitom et al. (2019) for MUSE data, we constructed four NH2 radial profiles through wedge-based aperture photometry across different quadrants, seen in the leftmost panel of Figure 11. We converted the NH2 flux to radial column density via Equation 2, in which Fcoma is the radial flux, g is the NH2 fluorescence efficiency from A’Hearn et al. (1995), and ∆is the geocentric distance in au.
Ncoma(ρ) = Fcoma(ρ) ∗1
g ∗(4π∆2) (2) We then utilise SBPY (Mommert et al., 2019) to implement the classic Haser (1957) model, described in equation 3, where Q0 is an a priori estimate of the NH2 production rate, ρ is cometocentric distance, vgas is gas expansion velocity, and Lp and Ld are known parent and daughter species scale lengths.
(exp (−ρ
) −exp (−ρ
)) (3)
Nhaser(ρ) = Q0 (4πρ2vgas) Ld Lp −Ld
Lp
Ld
We take values of vgas, Lp, and Ld previously tested on MUSE data from Table 2 in Bannister et al. (2020), and NH2 Q0 estimates during the 2009 67P apparition from Table 3 in Lara et al. (2011). We scaled Lp and Ld values with heliocentric distances. We utilise least squares fitting, varying Lp and Q0, to fit the Haser model (Nhaser(ρ)) to the observational data (Ncoma(ρ)). We cannot vary Ld due to the proximity of 67P, which limited the FoV to well within expected daughter species scale lengths (104-105 km). We attempted this process on all molecular maps, across all epochs, however, only the brightest NH2 maps bounding perihelion yielded satisfactory fits. Depicted across the middle four panels of Figure 11, we achieved highfidelity fits for each of the quadrants. Intriguingly, the fitted parent scale length is enhanced by a factor of 1.7 from the rest of the scale lengths in the coma, specifically in the NE quadrant that encompassed the large, curved, and stable NH2 pre-perihelion structure. Similarly, the profile for the NE quadrant was visually extended beyond those of the other quadrants. We computed uncertainties for the fitted parameters through the least square covariance matrix, and plotted them in the bottom right panel of Figure 34

11. While the uncertainties are large, it is expected that the quadrant with the largest parent scale length deviation would also have the largest uncertainty. If we were able to vary the daughter species scale length, we would achieve significantly lower uncertainties for our fits. Therefore, we can only report that parent scale lengths in the NE quadrant of 30 September 2021 are consistent with possible extended source contribution to the observed NH2 morphology. Notably, we find similar visual and scale length elongations in the NE quadrant across the pre-perihelion epochs (1.5× on 19 September, with the largest parent scale length ratio of 1.9 on 18 August, see Table 3). This suggests that the sustained pre-perihelion emission from this structure could be consistent with either partial or full emission from extended sources.