  We observed nine primary transits of the super-Earth exoplanet GJ 1214b in
several optical photometric bands from March to August 2012, with the goal of
constraining the short-wavelength slope of the spectrum of GJ 1214b. Our
observations were conducted on the Kuiper 1.55 m telescope in Arizona and the
STELLA-I robotic 1.2 m telescope in Tenerife, Spain. From the derived light
curves we extracted transit depths in R (0.65 {\mu}m), V (0.55 {\mu}m), and g'
(0.475 {\mu}m) bands. Most previous observations of this exoplanet suggest a
flat spectrum varying little with wavelength from the near-infrared to the
optical, corresponding to a low-scale-height, high-molecular-weight atmosphere.
However, a handful of observations around Ks band (~2.15 {\mu}m) and g-band
(~0.46 {\mu}m) are inconsistent with this scenario and suggest a variation on a
hydrogen- or water-dominated atmosphere that also contains a haze layer of
small particles. In particular, the g-band observations of de Mooij et al.
(2012), consistent with Rayleigh scattering, limit the potential atmosphere
compositions of GJ 1214b due to the increasing slope at optical wavelengths
(Howe & Burrows 2012). We find that our results overlap within errors the
short-wavelength observations of de Mooij et al. (2012), but are also
consistent with a spectral slope of zero in GJ 1214b in the optical wavelength
region. Our observations thus allow for a larger suite of possible atmosphere
compositions, including those with a high-molecular-weight and/or hazes.
