New Observations and a Possible Detection of Parameter Variations in the Transits of Gliese 436b

We present ground-based observations of the transiting Neptune-mass planet Gl 436b obtained with the 3.5 m telescope at Apache Point Observatory and other supporting telescopes. Included in this is an observed transit in early 2005, over 2 years before the earliest reported transit detection. We have compiled all available transit data to date and perform a uniform modeling using the JKTEBOP code. We do not detect any transit timing variations of amplitude greater than ~1 minute over the ~3.3 year baseline. We do however find possible evidence for a self-consistent trend of increasing orbital inclination, transit width, and transit depth, which supports the supposition that Gl 436b is being perturbed by another planet of lesssim12 M_⊕ in a nonresonant orbit.