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Gravitational lensing

Gaia16aye: the first binary microlensing event ever discovered towards the Galactic Plane

On 2016-08-05 the 1.2 mag brightening of an otherwise quiet stellar source triggered the Gaia16aye Gaia Science Alert, nicknamed Ayers Rock (19:40:01.13 +30:07:53.4, J2000). The previous 22 Gaia detections of the source (starting from 2014-10-30) show no variability greater than 0.05m RMS. The initial spectrophotometric observations did not clarify the nature of the observed flare (see ATel 9376) but the suspect of a bright microlensing event immediately rised and a spectrophotometric campaign started to monitor this source. Data obtained with the 1.5m telescope G.D. cassini by G. Altavilla (INAF-OABO) from Loiano at the beginning of September indicated a small rising trend in the light curves, as expected in the microlensing hypothesis. Moreover, in this hypothesis, modeling of the acquired light curves predicted another brightening (due to caustic crossing) in short times, hence intensively observations started again and G. Leto & R. Zanmar Sanchez (INAF-OACT) with the 0.8m robotic telescope APT2 from Serra la Nave observed a dramatic luminosity increase of Gaya16aye during the night between 17 and 18 September, 3 days after last observations in Loiano. This brightening confirmed the binary microlensing interpretation, and Gaia16aye results the first binary microlensing event ever discovered towards the Galactic Plane! Thanks to the light curve signatures secured by the photometric observations, we expect to characterize the size of the source in the units of the Einstein Radius, and in turn to estimate the mass of the lensing binary system. More information can be found in ATel 9507. The combined lightcurve and spectra can be found at

Image of Gaia16aye obtained at the 1.5m G.D. Cassini Telescope, Loiano.

Image of Gaia16aye obtained by G. Altavilla at the 1.5m G.D. Cassini Telescope, Loiano, on September 14, 2016.

Gaia16aye light curves

Gaia16aye light curves.