We report the discovery of a warm brown dwarf transiting a solar analog in the benchmark open cluster Ruprecht 147 (R147, 3 Gyr, 300 pc). Using K2 precision photometry, we detect a 0.96 Jupiter radius object transiting the solar analog every 5.29 days. With TRES radial velocities, we derive a mass of 35 times Jupiter's and an orbital eccentricity, e = 0.19. The solar analog is chromospherically overactive for its age, and given its 12.7 day rotation period, we suggest that the brown dwarf orbit is in the process of circularizing, which is spinning up the solar analog and enhancing its magnetic dynamo.

{"references": ["Curtis, J. L., Wolfgang, A., Wright, J. T., Brewer, J. M., & Johnson, J. A. 2013, AJ, 145, 134", "Mamajek, E. E., & Hillenbrand, L. A. 2008, ApJ, 687, 1264-1293", "Vanderburg, A. & Johnson, J.A. 2014, PASP, 126, 948"]}