Observations of the hydroxyl radical in C/2013 US10 (Catalina) at 18 cm Wavelength

The hydroxyl (OH) radical produced by photodissociation of water molecule is one of the most important indicators for cometary outgassing activity. The absorption lines of the OH radical at 1665 and 1667 MHz in the coma of comet C/2013 US10 Catalina were detected between 2015 December 3 and 5 by the Tian Ma Radio Telescope of Shanghai Astronomical Observatory. The source flux intensity was derived to be about -209 mJy km s^-1 and -86 mJy km s^-1 at 1665 MHz and 1667 MHz, respectively. The corresponding gas production rate was estimated to be (8.78 1.47) 10²⁸ H₂O s^-1 and (5.94 1.27) 10²⁸ H₂O s^-1, accordingly.