  The hot-Jupiter WASP-10b was reported by Maciejewski et al. (2011a,b) to show
transit timing variations (TTV) with an amplitude of ~ 3.5 minutes. These
authors proposed that the observed TTVs were caused by a 0.1 MJup perturbing
companion with an orbital period of ~ 5.23 d, and hence, close to the outer 5:3
mean motion resonance with WASP-10b. To test this scenario, we present eight
new transit light curves of WASP-10b obtained with the Faulkes Telescope North
and the Liverpool Telescope. The new light curves, together with 22 previously
published ones, were modelled with a Markov-Chain Monte-Carlo transit fitting
code. (...)
  Our homogeneously derived transit times do not support the previous claimed
TTV signal, which was strongly dependent on 2 previously published transits
that have been incorrectly normalised. Nevertheless, a linear ephemeris is not
a statistically good fit to the transit times of WASP-10b. We show that the
observed transit time variations are due to spot occultation features or
systematics. We discuss and exemplify the effects of occultation spot features
in the measured transit times and show that despite spot occultation during
egress and ingress being difficult to distinguish in the transit light curves,
they have a significant effect in the measured transit times. We conclude that
if we account for spot features, the transit times of WASP-10 are consistent
with a linear ephemeris with the exception of one transit (epoch 143) which is
a partial transit. Therefore, there is currently no evidence for the existence
of a companion to WASP-10b. Our results support the lack of TTVs of
hot-Jupiters reported for the Kepler sample.
