ASASSN-18fb: Discovery of a Bright Candidate Microlensing Event Located Away from the Galactic Bulge

ATel #11389; K. Z. Stanek (OSU), Subo Dong, P. Chen (KIAA-PKU), J. L. Prieto (Diego Portales; MAS), C. S. Kochanek, J. V. Shields, T. A. Thompson (OSU), B. J. Shappee (IfA-Hawaii), T. W.-S. Holoien (Carnegie Observatories), M. Stritzinger (Aarhus)
on 9 Mar 2018; 16:01 UT
Credential Certification: Krzysztof Stanek (stanek.32@osu.edu)

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During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN, Shappee et al. 2014), using data from the quadruple 14-cm "Cassius" telescope in CTIO, Chile, we detect a new transient source, most likely a bright microlensing event, located near the Galactic plane, but more than 60 degrees away from the Galactic center

 
Object       RA (J2000)    DEC (J2000)    Gal l (deg)   Gal b (deg)    Disc. UT Date   Disc. V mag  
ASASSN-18fb  11:12:05.36   -68:11:42.4      293.881      -7.084        2018-03-06.23     14.4 

ASASSN-18fb was discovered in images obtained on UT 2018-03-06.23 at V~14.4, and it is detected in subtracted V-band images going back to UT 2018-02-18.10. The event peaked in ASAS-SN V-band data on UT 2018-03-08.24, at V~13.8. We have retrieved image subtraction photometry time series at the location of ASASSN-18fb, but no previous outbursts or variability are detected at this position since ASAS-SN started observing this field in February 2016.

A microlensing fit to ASAS-SN V-band aperture photometry is shown here. Note that the lensed source is, most likely, significantly blended in ASAS-SN aperture photometry, as there are several stars listed in Gaia DR1 catalog within 10" radius.

Follow-up observations 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 grant AST-1515927, the Mt. Cuba Astronomical Foundation, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, the Chinese Academy of Sciences South America Center for Astronomy (CASSACA), and the Villum Fonden (Denmark).