Analyzing the onset of cometary activity by the Jupiter-family comet 2023 RN₃

We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Zwicky Transient Facility in addition to targeted follow-up observations from the Las Cumbres Observatory (LCO) and Liverpool Telescope to analyze the first observed instance of cometary activity by the newly discovered Jupiter-family comet C/2023 RN₃ (ATLAS), whose orbital dynamics place it close to residing on a Centaur-like orbit. Across our 7 month baseline, we observe an epoch of cometary activity commencing in 2023 August with an increase in brightness of >5.4 mag. The lightcurve of 2023 RN₃ indicates the presence of continuous cometary activity across our observations, suggesting the onset of a new period of sustained activity. We find no evidence of any outbursts on top of the observed brightening nor do we find any significant color evolution across our observations. 2023 RN₃ is visibly extended in LCO and Liverpool Telescope observations, indicating the presence of a spatially extended coma. Numerical integration of 2023 RN₃'s orbit reveals the comet to have recently undergone a slight increase in semimajor axis due to a planetary encounter with Jupiter; however, whether this orbital change could trigger 2023 RN₃'s cometary activity is unclear. Our estimate for the maximum dust production metric of Afρ ∼ 400 cm is consistent with previous measurements for the Jupiter-family comet and Centaur populations.