* Astronomy

Title: Discovery of a Very Bright, Nearby Gravitational Microlensing Event
Authors: B. Scott Gaudi, Joseph Patterson, David S. Spiegel, Thomas Krajci, R. Koff, G. Pojmanski, Subo Dong, Andrew Gould, Jose L. Prieto, Cullen H. Blake, Peter W. A. Roming, David P. Bennett, Joshua S. Bloom, David Boyd, Pierre de Ponthiere, N. Mirabal, Christopher W. Morgan, Ronald R. Remillard, T. Vanmunster, R. Mark Wagner, Linda C. Watson

We report the serendipitous detection of a very bright, very nearby microlensing event. In late October 2006, an otherwise unremarkable A0 star at a distance ~1 kpc (GSC 3656-1328) brightened achromatically by a factor of nearly 40 over the span of several days and then decayed in an apparently symmetrical way. We present a light curve of the event based on optical photometry from the Centre for Backyard Astrophysics and the All Sky Automatic Survey, as well as near-infrared photometry from the Peters Automated Infrared Imaging Telescope. This light curve is well-fit by a generic microlensing model. We also report optical spectra, and Swift X-ray and UV observations that are consistent with the microlensing interpretation. We discuss and reject alternative explanations for this variability. The lens star is probably a low-mass star or brown dwarf, with a relatively high proper motion of >20 mas/yr, and may be visible using precise optical/infrared imaging taken several years from now. We demonstrate that a modest, all-sky survey telescope could detect ~10 such events per year, which would enable searches for very low-mass planetary companions to relatively nearby stars.

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