Detection of OH maser emission in the 71-year periodic comet 12P/Pons-Brooks using the 40-m Thai National Radio Telescope (TNRT)
Nobuyuki Sakai, Saran Poshyachinda, Koichiro Sugiyama, Wiphu Rujopakarn, Boonrucksar Soonthornthum, Apichat Leckngam, Busaba Kramer, Phrudth Jaroenjittichai, Bannawit Pimpanuwat, Dan Singwong, Kitipoom Kanjana, Nikom Prasert, Songklod Punyawarin, Spiro Sarris, Teep Chairin, Kamorn Bandudej, Chalunthon Nuchur, Haseng Sani, Nattawit Chanwedchasart, Pathit Chatuphot, Prachayapan Jiraya, Saharat Sathipjan, Adirake Eakwan, Chayanin Larkaew, Settasak Naewchan, Pichate Pha-Kham, Siritida Duangbuppha, Thodsawat Chaichana, Attapon Bunwong, Panupan Doomcome, Anya Poonnawatt, Warakorn Noisapung, Pathorn Sathapornvajana, Naphat Yawilerng, Thita Dilokthanakul, Kritsada Angkaew, Nattawut Chaiwongwan, Jittimat Khanchaiyapoom, Hideyuki Kobayashi, Yu-An Chen, Nawamin Intrarat, Gundolf Wieching, Ewan Barr, Jason Wu, Niclas Esser, Tobias Winchen, Pablo Vicente
TL;DR
Using the 40-m Thai National Radio Telescope, the authors detected OH 18-cm maser emission from 12P/Pons-Brooks at 1665 and 1667 MHz on three epochs in March 2024, before perihelion. They derive $Q_{\rm OH}$ values of $(4.28 \pm 0.30) \times 10^{29}$ s$^{-1}$, $(5.21 \pm 0.42) \times 10^{29}$ s$^{-1}$, and $(3.36 \pm 0.43) \times 10^{29}$ s$^{-1}$ for March 22, 27, and 29, respectively, noting day-to-day fluctuations and a gradual rise toward perihelion when combined with prior estimates. The OH-line shapes yield a water expansion velocity $V_p$ of $1.55 \pm 0.14$ km s$^{-1}$ (best constrained on March 22), with a heuristic expectation of $V_p \approx 1.58^{+0.09}_{-0.08}$ km s$^{-1}$ at $r_h \approx 0.959$ au and $Q_{\rm OH} \approx 4.28 \times 10^{29}$ s$^{-1}$. The results validate the TNRT's capability for timely cometary radio monitoring and motivate creation of a TNRT Cometary Database (TNRT CDB) to enable cross-comparison with optical and other radio measurements and to support broader cometary studies.
Abstract
Although the optical cometary database is extensive, the radio database is limited. The 18-cm OH maser observations of comets allow us to determine (i) the production rate of OH ($Q_{\rm{OH}}$) and (ii) the water expansion velocity, for each comet. To reveal the physical properties of the periodic comet 12P/Pons-Brooks, we conducted the OH maser observations of the comet using the 40-m TNRT (Thai National Radio Telescope) on March 22nd, 27th and 29th, 2024 before the perihelion passage on April 21st, 2024. We successfully detected 1665 and 1667 MHz OH maser emissions from the comet. The average OH production rates of 12P/Pons-Brooks were determined as 4.28$\pm$0.30 $\times$ 10$^{29}$ sec$^{-1}$, 5.21$\pm$0.42 $\times$ 10$^{29}$ sec$^{-1}$, and 3.36$\pm$0.43 $\times$ 10$^{29}$ sec$^{-1}$ for March 22nd, 27th and 29th, respectively. Combining our results with previous estimates, we find that the OH production rate of 12P/Pons-Brooks shows some fluctuations on timescales of a few days, but gradually increases on longer timescales as the comet approaches the last perihelion. The water expansion velocities of the comet were determined to be 1.55$\pm$0.14 km s$^{-1}$, 1.55$\pm$0.35 km s$^{-1}$, and 2.02$^{+0.47}_{-0.45}$ km s$^{-1}$ for the observations on March 22nd, 27th and 29th, respectively. The reason why the errors are different is because the signal to noise ratio is different for each OH maser emission. All expansion velocities are consistent with the individual results of the heuristic law (Tseng et al. 2007) within errors.