Abstract During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now ...possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.
Abstract We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a disk source rather than the traditional bulge microlensing fields. ...Our primary analysis yields a Jovian planet with M p = 0.59 − 0.05 + 0.15 M J at a projected orbital separation r ⊥ = 1.4 − 0.3 + 0.8 au, and the host is a ∼1.1 M ⊙ turnoff star at ∼1.3 kpc. At r ′ ≈ 14 , the host is far brighter than any previously discovered microlensing planet host, opening up the opportunity to test the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet’s orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the “inner–outer correlation” inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius θ E but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to the definitive characterization of the lens system.
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
Gaia
18cbf 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
t
E
= 491.41
−84.94
+128.31
days for the best solution and
t
E
= 453.74
−105.74
+178.69
days for the second best. Assuming Galaxy priors, this translates to the most probable lens masses of
M
L
= 2.65
−1.48
+5.09
M
⊙
and
M
L
= 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.
Gravitational microlensing is a phenomenon that allows us to observe dark remnants of stellar evolution even if they no longer emit electromagnetic radiation. In particular, it can be useful to ...observe solitary neutron stars or stellar-mass black holes, providing a unique window through which to understand stellar evolution. Obtaining direct mass measurements with this technique requires precise observations of both the change in brightness and the position of the microlensed star and the European Space Agency's Gaia satellite can provide both. We analysed events published in Gaia Data Release 3 (GDR3) microlensing catalogue using publicly available data from different surveys. Here we describe our selection of candidate dark lenses, where we suspect the lens is a white dwarf (WD), a neutron star (NS), a black hole (BH), or a mass-gap object, with a mass in a range between the heaviest NS and the least massive BH. We estimated the mass of the lenses using information obtained from the best-fitting microlensing models, the Galactic model and the expected distribution of the parameters. We found eight candidates for WDs or NS, and two mass-gap objects.
Identifying black holes is essential for comprehending the development of stars and uncovering novel principles of physics. Gravitational microlensing provides an exceptional opportunity to examine ...an undetectable population of black holes in the Milky Way. In particular, long-lasting events are likely to be associated with massive lenses, including black holes. We present an analysis of the Gaia18ajz microlensing event, reported by the Gaia Science Alerts system, which has exhibited a long timescale and features indicative of the annual microlensing parallax effect. Our objective is to estimate the parameters of the lens based on the best-fitting model. We utilized photometric data obtained from the Gaia satellite and terrestrial observatories to investigate a variety of microlensing models and calculate the most probable mass and distance to the lens, taking into consideration a Galactic model as a prior. Subsequently, weapplied a mass-brightness relation to evaluate the likelihood that the lens is a main sequence star. We also describe the DarkLensCode (DLC), an open-source routine which computes the distribution of probable lens mass, distance and luminosity employing the Galaxy priors on stellar density and velocity for microlensing events with detected microlensing parallax. We modelled Gaia18ajz event and found its two possible models with most likely Einstein timescale of \(316^{+36}_{-30}\) days and \(299^{+25}_{-22}\) days. Applying Galaxy priors for stellar density and motion, we calculated the most probable lens mass of \(4.9^{+5.4}_{-2.3} M_\odot\) located at \(1.14^{+0.75}_{-0.57}\,\text{kpc}\) or \(11.1^{+10.3}_{-4.7} M_\odot\) located at \(1.31^{+0.80}_{-0.60}\,\text{kpc}\). Our analysis of the blended light suggests that the lens is likely a dark remnant of stellar evolution, rather than a main sequence star.
During the last 25 years, hundreds of binary stars and planets have been discovered towards the Galactic Bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now ...possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at \(\le2.0\) kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.
We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a nearby disk source at ~2.5 kpc rather than the traditional bulge ...microlensing fields. Our primary analysis yields a Jovian planet with M_p = 0.50 +/- 0.05 M_J at a projected orbital separation r_perp = 1.63 +/- 0.17 AU. The host is a turnoff star with mass 1.24 +/- 0.06 M_sun and distance of 1.35 +/- 0.09 kpc, and at r'~14, it is far brighter than any previously discovered microlensing planet host, opening up the opportunity of testing the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet's orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the "inner-outer correlation" inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius theta_E, but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to definitive characterization of the lens system.
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.
In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of \(\sim 950\) microlensing events observed by the Spitzer Space Telescope between 2014 ...and 2019. In this study we focus on a sub-sample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of \(2.98^{+1.75}_{-1.28}~M_{\odot}\), \(4.65^{+3.12}_{-2.08}~M_{\odot}\), \(3.15^{+0.66}_{-0.64}~M_{\odot}\) and \(1.4^{+0.75}_{-0.55}~M_{\odot}\), respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the time-scale (\(t_{\rm E}\)) vs. parallax (\(\pi_{\rm E}\)) diagram to derive constraints on the population of lenses in general and massive remnants in particular.
