Pre-perihelion radio observations of comet 12P/Pons-Brooks with Tianma radio telescope

TL;DR

This study used the Tianma radio telescope to observe comet 12P/Pons-Brooks during its 2024 approach, detecting water and possibly ammonia emissions to understand its volatile outgassing and outburst behavior.

Contribution

First radio observations of comet 12P/Pons-Brooks during its 2024 apparition, providing insights into its volatile composition and outburst mechanisms.

Findings

Detected OH lines with 4σ significance, indicating water outgassing.

Tentative 3σ detection of NH₃ during outburst suggests subsurface volatile activity.

Water production rates align with previous measurements.

Abstract

{The multiple outburst events of comet 12P/Pons-Brooks during its 2024 apparition offer a unique window into highly-active volatile releasing processes not observable during quiescent periods. We performed radio observations of comet 12P/Pons-Brooks with the Tianma-65m radio telescope, targeting the OH and NH$_3$ inversion lines at 18-cm and 1.3-cm, respectively. By monitoring 12P at different heliocentric distances on its inbound journey, we aim to provide insights into the comet's volatile composition and outburst behavior. Four observations were carried out between December 2023 and March 2024 when the comet was approaching the Sun from 2.22 AU to 1.18 AU. We conducted 18-cm OH lines observations on 4 single days using the cryogenically cooled receiver system of the telescope to derive $\rm H_{2}O$ production rate. During 12P's outburst on December 14, we also conducted observations targeting the $\rm NH_{3}$ emission. OH 18-cm lines were clearly detected with a signal-to-noise ratio of $\sim$4$\sigma$ (peak intensity). A tentative detection of $\rm NH_{3}$ was made at the $\sim$$3\sigma$ level during the outburst phase, but the detection needs to be further verified. Our observations provide information on the outgassing behavior of 12P/Pons-Brooks during its 2024 apparition. The water production rate of 12P, derived from the 18-cm OH lines is consistent with measurements obtained in other works. The possible detection of $\rm NH_{3}$ during an outburst suggests possible connections between subsurface volatile reservoir and the outburst mechanism. These results could further our understanding of the composition and activity of Halley-type comets.