ASAS-SN Discovery of ASASSN-20mg, a Likely Bright Microlensing Event in the Galactic Disk
ATel #14037; D. Desai, K. Z. Stanek, T. Jayasinghe, Z. Way, C. S. Kochanek, T. A. Thompson (OSU), B. J. Shappee (Univ. of Hawaii), T. W.-S. Holoien (Carnegie Observatories), J. L. Prieto (Diego Portales; MAS), Subo Dong (KIAA-PKU), M. Stritzinger (Aarhus)
on 22 Sep 2020; 20:10 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)
Subjects: Optical, Microlensing Event, Transient
During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014, Kochanek et al. 2017), using data from the quadruple 14-cm "Payne" telescope, we identified a previously non-variable stellar source undergoing a significant brightening episode. The location of ASASSN-20mg (matching with a Gaia DR2 source: RAJ2000=264.63879813504, DEJ2000=-48.40000351866, source_id=5948438862137172736, d~4700 pc, Teff=4570 K) was first observed by ASAS-SN on UT 2016-03-08 and identified as a transient on UT 2020-09-21.83. The line of sight extinction to ASASSN-20mg is A_V~0.59 mag (A_g~0.71 mag) (Schlafly & Finkbeiner, 2011). ASASSN-20mg is located towards the Galactic center, and close to the Galactic plane with (l,b)~(342.610,-8.988). Presently, ASASSN-20mg has more than ~1,850 ASAS-SN epochs.
The optical source coincident with ASASSN-20mg did not show any previous, significant variability and has a quiescent mean magnitude of g~14.9 (V~14.3), as seen in the complete ASAS-SN V/g-band light curve. The latest ASAS-SN photometry shows that ASASSN-20mg brightened from g~14.7 on UT 2020-09-11 to g~13.6 on UT 2020-09-21. Based on the light curve morphology and the lack of similar variability in the archival data, ASASSN-20mg might be a Galactic disk microlensing event.
Follow-up observations of this interesting object are strongly encouraged.
We would like to thank Las Cumbres Observatory and its staff for their continued support of ASAS-SN. ASAS-SN is funded in part by the Gordon and Betty Moore Foundation through grant GBMF5490 to the Ohio State University, NSF grants AST-1515927 and AST-1908570, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics at OSU, the Chinese Academy of Sciences South America Center for Astronomy, and the Villum Fonden (Denmark).
