Periodic variation in the water production of comet C/2001 Q4 (NEAT) observed with the Odin satellite

Context. Comet C/2001 Q4 (NEAT) was extensively studied with the 1.1-m submillimetre telescope of the Odin satellite. The H2O line at 557 GHz was regularly observed from 6 March to 16 May 2004 and nearly continuously monitored during 3 periods between 26 April and 2 May 2004.Aims. This last set of data shows periodic variations in the line intensity, and we looked for characterising the long- and short-term behaviour of this comet.Methods. We used the variance ratio method and minimization to find the period of variation in the water production rate and simulations to infer its amplitude at the nucleus surface.Results. A 40% periodic variation in the water production rate is measured with a period of day ( h). The comet also exhibits a seasonal effect with a mean peak of outgassing around molec. s-1 taking place about 18 days before perihelion.