Gaia19bld is a highly magnified microlensing event in the Galactic disk
ATel #12948; K. Rybicki, L. Wyrzykowski, P. Zielinski, M. Ratajczak (Warsaw University Astronomical Observatory), E. Bachelet, R. Street (LCOGT), M. Hundertmark, Y. Tsapras (Uni. Heidelberg), A. Udalski (Warsaw University Astronomical Observatory, on behalf of the OGLE team), J. Hambsch (ROAD Observatory), M. Konacki, R. Pawlaszek, A. Kinasz (CAMK, on behalf of the Solaris team)
on 19 Jul 2019; 13:13 UT
Credential Certification: Lukasz Wyrzykowski (wyrzykow@astrouw.edu.pl)
Subjects: Optical, Black Hole, Microlensing Event, Star, Transient, Gravitational Lensing
We report on the discovery and follow-up of a very bright and highly magnified microlensing event Gaia19bld (AT2019dqb at IAU's Transient Name Server). The event is located in the Galactic disk (RA=12:37:32.56 DEC=-66:06:40.90) at galactic coordinates (l,b)=(301.5, -3.3). It has been detected and announced by the Gaia Science Alerts programme (Rixon et al. ATEL #6593) on 2019-04-18 18:12:57 UT (JD=2458592.259) at G = 14.4 mag, 0.4 mag above the baseline brightness of G=14.8 mag. It has been then followed-up with the Gaia Science Alerts network, mostly with the Las Cumbres Observatory (LCO) 1-m telescopes in the South African Astronomical Observatory, Siding Spring Observatory in Australia and Cerro Tololo International Observatory in Chile, in V and I filters. The event was also observed within the OGLE-IV project on the 1.3-m Warsaw Telescope located at Las Campanas Observatory in Chile, which shows the object remained flat since 2013 until its rise in early 2019. Regular observations are also carried out by 0.4m ROAD Observatory, San Pedro de Atacama, Chile and with Solaris global network of 0.5m telescopes.
The event reached its peak at JD~2458681.3 (2019-07-16 21:00 UT) with G=10.4 mag and I=9.0 mag. The microlensing lightcurve exhibits strong finite source effect but the model parameters and thus the nature of the source and the lens are still uncertain.
A high-resolution (R~50000) optical (400-900 nm) spectrum was acquired using the LCO Network of Robotic Echelle Spectrographs (NRES). The spectrum was obtained at Cerro Tololo, Chile at the 2019-07-16 01:04:57 UT. The spectrum shows features consistent with a single K3 star with luminosity class Ib or II. The fit of the synthetic spectrum reveals the best match with supergiant with Teff=4157+-68 K, logg=1.22+-0.46 and [M/H]=0.52+-0.09 dex.
We strongly encourage further photometric and spectroscopic follow-up of this spectacular event.
We acknowledge ESA Gaia (http://cosmos.esa.int/gaia), DPAC (cosmos.esa.int/web/gaia/dpac) and the DPAC Photometric Science Alerts Team (http://gaia.ac.uk/selected-gaia-science-alerts). We also acknowledge the use of the Cambridge Photometric Calibration Server (http://gsaweb.ast.cam.ac.uk/followup), developed and maintained by Lukasz Wyrzykowski, Sergey Koposov, Arancha Delgado, Pawel Zielinski and Kris Rybicki, funded by the European Union's Horizon 2020 research and innovation programme under grant agreement No 730890 (OPTICON).
Follow-up observations of Gaia19bld
