  In this Letter we present observations of recent HAT-P-13b transits. The
combined analysis of published and newly obtained transit epochs shows evidence
for significant transit timing variations since the last publicly available
ephemerides. Variation of transit timings result in a sudden switch of transit
times. The detected full range of TTV spans ~0.015 days, which is significantly
more than the known TTV events exhibited by hot Jupiters. If we have detected a
periodic process, its period should be at least ~3 years because there are no
signs of variations in the previous observations. This argument makes unlikely
that the measured TTV is due to perturbations by HAT-P-13c.
