The rapid outbursting star GM CEP:: An exor in Tr 37?

We present optical, IR, and millimeter observations of the solar-type star 13-277, also known as GM Cep, in the 4 Myr old cluster Tr 37. GM Cep experiences rapid magnitude variations of more than 2 mag at optical wavelengths. We explore the causes of the variability, which seem to be dominated by strong increases in the accretion, being similar to EXor episodes. The star shows high, variable accretion rates (up to similar to 10(-6) M (circle dot) yr(-1)) and signs of powerful winds, and it is a very fast rotator (V sin i similar to 43 km s(-1)). Its strong mid-IR excesses reveal a very flared disk and/ or a remnant envelope, most likely out of hydrostatic equilibrium. The 1.3 mm fluxes suggest a relatively massive disk (M-D similar to 0.1 M-circle dot). Nevertheless, the millimeter mass is not enough to sustain increased accretion episodes over large timescales, unless the mass is underestimated due to significant grain growth. We finally explore the possibility of GM Cep having a binary companion, which could trigger disk instabilities producing the enhanced accretion episodes.