I. M. Coulson, Yi-Jehng Kuan, Steven B. Charnley, Martin Cordiner, Yo-Ling Chuang, Y L. Lee, Min-Kai Lin, Stefanie N. Milam, Bannawit Pimpanuwat, Nathan X. Roth, Michał Żółtowski
ABSTRACT We report the detection of HCN($J=3-2$) rotational emission from comet 3I/ATLAS at a heliocentric distance of 2.13 au with the James Clerk Maxwell Telescope (JCMT). Observations were conducted between 2025 August 7 and 2025 September 14 (ut) using the $^{^{\prime }}\, \overline{U}\, ^{^{\prime }}\, \overline{u}$ heterodyne receiver and ACSIS (Auto Correlation Spectral Imaging System) spectroscopic backend. The HCN line was detected at $> 6 \sigma$ on 2025 September 14 (ut) and a production rate of $Q({\rm HCN})=(4.0\pm 1.7)\times 10^{25}$ s$^{-1}$ was derived by non-LTE radiative transfer modelling. Preliminary estimates of the HCN/H$_2$O and CN/HCN abundance ratios suggest values similar to Solar system comets.