Lens parameters for Gaia18cbf -- a long gravitational microlensing event in the Galactic plane

• Main Authors: Kruszyńska, Katarzyna, Wyrzykowski, Ł, Rybicki, K. A, Maskoliūnas, M, Bachelet, E, Rattenbury, N, Mróz, P, Zieliński, P, Howil, K, Kaczmarek, Z, Hodgkin, S. T, Ihanec, N, Gezer, I, Gromadzki, M, Mikołajczyk, P, Stankevičiūtė, A, Čepas, V, Pakštienė, E, Šiškauskaitė, K, Zdanavičius, J, Bozza, V, Dominik, M, Jaimes, R. Figuera, Fukui, A, Hundertmark, M, Narita, N, Street, R, Tsapras, Y, Bronikowski, M, Jabłońska, M, Jabłonowska, A, Ziółkowska, O
• Format: Journal Article
• Language: English
• Published: 07-04-2022
• Subjects: Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.2111.08337

A&A 662, A59 (2022) Context: The timescale of a microlensing event scales as a square root of a
lens mass. Therefore, long-lasting events are important candidates for massive
lenses, including black holes.
Aims: Here we present the analysis of the Gaia18cbf microlensing event
reported by the Gaia Science Alerts system. It exhibited a long timescale and
features that are common for the annual microlensing parallax effect. We deduce
the parameters of the lens based on the derived best fitting model.
Methods: We used photometric data collected by the Gaia satellite as well as
the follow-up data gathered by the ground-based observatories. We investigated
the range of microlensing models and used them to derive the most probable mass
and distance to the lens using a Galactic model as a prior. Using known
mass-brightness relation we determined how likely it is that the lens is a
main-sequence (MS) star.
Results: This event is one of the longest ever detected, with the Einstein
timescale of $t_\mathrm{E}=491.41^{+128.31}_{-84.94}$ days for the best
solution and $t_\mathrm{E}=453.74^{+178.69}_{-105.74}$ days for the
second-best. Assuming Galaxy priors, this translates to the most probable lens
mass of $M_\mathrm{L} = 2.65^{+5.09}_{-1.48} M_\odot$ and $M_\mathrm{L} =
1.71^{+3.78}_{-1.06} M_\odot$, respectively.
The limits on the blended light suggest that this event was most likely not
caused by a MS star, but rather by a dark remnant of stellar evolution.