Gaia16bnn is a microlensing event in the Southern Bulge

ATel #9783; A. Hamanowicz (Warsaw University Astronomical Observatory, Poland), N. Britavskiy (Department of Astronomy and Astronomical Observatory, Odessa National University, Ukraine ), L. Wyrzykowski, K. A. Rybicki (Warsaw University Astronomical Observatory, Poland), David Buckley (South African Astronomical Observatory), Patricia Whitelock (South African Astronomical Observatory)
on 23 Nov 2016; 16:05 UT
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)

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We conducted the spectroscopic classification of a transient discovered by Gaia towards the Southern part of the Galactic Bulge. The transient was reported on the Gaia Photometric Science Alerts webpage as a 1 mag increase on an otherwise constant star.

The spectra were obtained using the Robert Stobie Spectrograph (RSS) on the South African Large Telescope (SALT). The spectrum is consistent with a GII or GIII-type star, therefore the most likely explanation for its brightening is gravitational microlensing effect. We assume the observed spectrum is of the source star, which was amplified several times. We note that the transient is positioned just outside of the OGLE-IV Bulge survey footprint at galactic latitude of -12.2 deg and is located relatively close to the stream of stars from the Sagittarius Dwarf galaxy.

Name | RA (J2000) | Dec (J2000) | Gaia Alerting Date | Gaia Alert. Mag | Obs. Date | Notes |
Gaia16bnn | 18:30:42.21 | -37:04:16.93 | 2016-10-14 | 16.93 | 2016-10-19 | GII/GIII-type star |

Further photometric and spectroscopic follow-up is encouraged as the event is still possibly on the rise, according to the data from Gaia

We acknowledge ESA Gaia, DPAC and the Photometric Science Alerts Team.