Table 1
Best-fitted linear models for the brightening trend.
| Time range | Aperture radius (104 km) | Colour index C | Slope  (mag yr−1) |
χ2 | Degree of freedom | |
|---|---|---|---|---|---|---|
| <2023 | 2.5 | g–r= | +0.75 ± 0.07 | −0.17 ± 0.04 | 0.34 | 5 |
| 3.0 | +0.72 ± 0.07 | −0.15 ± 0.04 | 0.46 | |||
| 3.5 | +0.73 ± 0.07 | −0.14 ± 0.04 | 0.55 | |||
| 4.0 | +0.76 ± 0.07 | −0.14 ± 0.03 | 0.68 | |||
| >2023 | 2.5 | r–i= | +0.33 ± 0.06 | +0.24 ± 0.08 | 10.01 | 21 |
| 3.0 | +0.32 ± 0.06 | +0.17 ± 0.06 | 14.16 | |||
| 3.5 | +0.37 ± 0.08 | +0.22 ± 0.08 | 19.87 | |||
| 4.0 | +0.43 ± 0.08 | +0.24 ± 0.08 | 25.18 | |||
| Mean ± standard deviation | g–r= | +0.74 ± 0.02 | −0.15 ± 0.01 | – | – | |
| r–i= | +0.35 ± 0.05 | +0.21 ± 0.04 | – | – | ||
Notes. The intercepts of the best-fitted linear models are not presented, as they are of little interest. The reported errors are 1σ formal uncertainties, properly propagated from the uncertainties in the absolute magnitude, while the errors on the weighted mean values are the weighted standard deviations of the best-fit parameters across multiple apertures. For comparison, the Sun has a colour of g − r = +0.46 ± 0.03 and r − i = +0.12 ± 0.03 (Willmer 2018), and the median colour of comets reported by Solontoi et al. (2012) is g − r = +0.57 ± 0.05 and r − i = +0.22 ± 0.07.
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