  GJ3470b is a hot Neptune exoplanet orbiting an M dwarf and the first
sub-Jovian planet to exhibit Rayleigh scattering. We present transit timing
variation (TTV) and transmission spectroscopy analyses of multi-wavelength
optical photometry from 2.4-m and 0.5-m telescopes at the Thai National
Observatory, and the 0.6-m PROMPT-8 telescope in Chile. Our TTV analysis allows
us to place an upper mass limit for a second planet in the system. The presence
of a hot Jupiter with a period of less than 10 days or a planet with an orbital
period between 2.5 and 4.0 days are excluded. Combined optical and
near-infrared transmission spectroscopy favour an H/He dominated haze (mean
molecular weight 1.08$\pm$0.20) with high particle abundance at high altitude.
We also argue that previous near-infrared data favour the presence of methane
in the atmosphere of GJ3470b.
