  We report the discovery of a transiting planet with an orbital period of
3.05d orbiting the star TYC 7247-587-1. The star, WASP-41, is a moderately
bright G8V star (V=11.6) with a metallicity close to solar
([Fe/H]=-0.08+-0.09). The star shows evidence of moderate chromospheric
activity, both from emission in the cores of the CaII H and K lines and
photometric variability with a period of 18.4d and an amplitude of about 1%. We
use a new method to show quantitatively that this periodic signal has a low
false alarm probability. The rotation period of the star implies a
gyrochronological age for WASP-41 of 1.8Gyr with an error of about 15%. We have
used a combined analysis of the available photometric and spectroscopic data to
derive the mass and radius of the planet (0.92+-0.06M_Jup, 1.20+-0.06R_Jup).
Further observations of WASP-41 can be used to explore the connections between
the properties of hot Jupiter planets and thelevel of chromospheric activity in
their host stars.
