Lens parameters for Gaia18cbf - a long gravitational microlensing event in the Galactic plane
Mróz, P.; Gromadzki, M.; Narita, N.; Hodgkin, S. T.; Kruszyńska, K.; Rybicki, K. A.; Wyrzykowski, Ł.; Ihanec, N.; Bachelet, E.; Zieliński, P.; Gezer, I.; Tsapras, Y.; Hundertmark, M.; Dominik, M.; Fukui, A.; Bozza, V.; Jabłońska, M.; Figuera Jaimes, R.; Mikołajczyk, P.; Rattenbury, N.; Street, R.; Ziółkowska, O.; Pakštienė, E.; Bronikowski, M.; Maskoliūnas, M.; Howil, K.; Kaczmarek, Z.; Zdanavičius, J.; Čepas, V.; Šiškauskaitė, K.; Stankevičiūtė, A.; Jabłonowska, A.
Poland, Lithuania, United States, New Zealand, United Kingdom, Italy, Chile, Japan, Spain, Germany, Slovenia
Abstract
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 a 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 tE = 491.41−84.94+128.31 days for the best solution and tE = 453.74−105.74+178.69 days for the second best. Assuming Galaxy priors, this translates to the most probable lens masses of ML = 2.65−1.48+5.09 M⊙ and ML = 1.71−1.06+3.78 M⊙, 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.