High-cadence observations of the Galactic bulge by the microlensing surveys led to the discovery of a handful of extremely short-timescale microlensing events that can be attributed to free-floating ...or wide-orbit planets. Here, we report the discovery of another strong free-floating planet candidate, which was found from the analysis of the gravitational microlensing event OGLE-2019-BLG-0551. The light curve of the event is characterized by a very short duration ( 3 days) and a very small amplitude ( 0.1 mag). From modeling of the light curve, we find that the Einstein timescale, day, is much shorter, and the angular Einstein radius, as, is much smaller than those of typical lensing events produced by stellar-mass lenses ( days, mas), indicating that the lens is very likely to be a planetary-mass object. We conduct an extensive search for possible signatures of a companion star in the light curve of the event, finding no significant evidence for the putative host star. For the first time, we also demonstrate that the angular Einstein radius of the lens does not depend on blending in the low-magnification events with strong finite source effects.
ABSTRACT
Only a few wide-orbit planets around old stars have been detected, which limits our statistical understanding of this planet population. Following the systematic search for planetary ...anomalies in microlensing events found by the Korea Microlensing Telescope Network, we present the discovery and analysis of three events that were initially thought to contain wide-orbit planets. The anomalous feature in the light curve of OGLE-2018-BLG-0383 is caused by a planet with mass ratio q = 2.1 × 10−4 and a projected separation s = 2.45. This makes it the lowest mass-ratio microlensing planet at such wide orbits. The other two events, KMT-2018-BLG-0998 and OGLE-2018-BLG-0271, are shown to be stellar binaries (q > 0.1) with rather close (s < 1) separations. We briefly discuss the properties of known wide-orbit microlensing planets and show that the survey observations are crucial in discovering and further statistically constraining such a planet population.
Searches for gravitational microlensing events are traditionally concentrated on the central regions of the Galactic bulge but many microlensing events are expected to occur in the Galactic plane, ...far from the Galactic Center. Owing to the difficulty in conducting high-cadence observations of the Galactic plane over its vast area, which are necessary for the detection of microlensing events, their global properties were hitherto unknown. Here, we present results of the first comprehensive search for microlensing events in the Galactic plane. We searched an area of almost 3000 square degrees along the Galactic plane ( , 0° < l < 50°, 190° < l < 360°) observed by the Optical Gravitational Lensing Experiment (OGLE) during 2013-2019 and detected 630 events. We demonstrate that the mean Einstein timescales of Galactic plane microlensing events are on average three times longer than those of Galactic bulge events, with little dependence on the Galactic longitude. We also measure the microlensing optical depth and event rate as a function of Galactic longitude and demonstrate that they exponentially decrease with the angular distance from the Galactic Center (with the characteristic angular scale length of 32°). The average optical depth decreases from 0.5 × 10−6 at l = 10° to 1.5 × 10−8 in the Galactic anticenter. We also find that the optical depth in the longitude range 240° < l < 330° is asymmetric about the Galactic equator, which we interpret as a signature of the Galactic warp.
Abstract
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered by the Optical Gravitational Lensing Experiment survey. The spatial distribution of the ...Mira stars is analyzed with a model containing three barred components that include the X-shaped boxy component in the Galactic center (GC) and an axisymmetric disk. We take into account the distance uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R
0
= 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the Sun–GC line of sight is
θ
= 20.°2 ± 0.°6(stat.) ± 0.°7(sys.). We present, for the first time, a detailed three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations. Our analysis provides independent evidence for both the X-shaped bulge component and the flaring disk (being plausibly warped). We provide the complete data set of properties of Miras that were used for calculations in this work. The table includes mean brightness and amplitudes in nine photometric bands (covering a range of wavelengths from 0.5 to 12
μ
m), photometric chemical type, estimated extinction, and calculated distance with its uncertainty for each Mira variable. The median distance accuracy to a Mira star is at the level of 6.6%.
Abstract Measurements of the microlensing optical depth and event rate toward the Large Magellanic Cloud (LMC) can be used to probe the distribution and mass function of compact objects in the ...direction toward that galaxy—in the Milky Way disk, the Milky Way dark matter halo, and the LMC itself. The previous measurements, based on small statistical samples of events, found that the optical depth is an order of magnitude smaller than that expected from the entire dark matter halo in the form of compact objects. However, these previous studies were not sensitive to long-duration events with Einstein timescales longer than 2.5–3 yr, which are expected from massive (10–100 M ⊙ ) and intermediate-mass (10 2 –10 5 M ⊙ ) black holes. Such events would have been missed by the previous studies and would not have been taken into account in calculations of the optical depth. Here, we present the analysis of nearly 20 yr long photometric monitoring of 78.7 million stars in the LMC by the Optical Gravitational Lensing Experiment (OGLE) from 2001 through 2020. We describe the observing setup, the construction of the 20 yr OGLE data set, the methods used for searching for microlensing events in the light-curve data, and the calculation of the event detection efficiency. In total, we find 16 microlensing events (13 using an automated pipeline and three with manual searches), all of which have timescales shorter than 1 yr. We use a sample of 13 events to measure the microlensing optical depth toward the LMC τ = (0.121 ± 0.037) × 10 −7 and the event rate Γ = (0.74 ± 0.25) × 10 −7 yr −1 star −1 . These numbers are consistent with lensing by stars in the Milky Way disk and the LMC itself, and they demonstrate that massive and intermediate-mass black holes cannot comprise a significant fraction of the dark matter.
Abstract We use the spectroscopic data collected by the Magellanic Quasars Survey (MQS) and the photometric V - and I -band data from the Optical Gravitational Lensing Experiment (OGLE) to measure ...the physical parameters for active galactic nuclei (AGNs) located behind the Magellanic Clouds. The flux-uncalibrated MQS spectra were obtained with the 4 m Anglo-Australian Telescope and the AAOmega spectroscope ( R = 1300) in a typical ∼1.5 hr visit. They span a spectral range of 3700–8500 Å and have signal-to-noise ratios in a range of 3–300. We report the discovery and observational properties of 161 AGNs in this footprint, which expands the total number of spectroscopically confirmed AGNs by MQS to 919. After the conversion of the OGLE mean magnitudes to the monochromatic luminosities at 5100, 3000, and 1350 Å, we were able to reliably measure the black hole masses for 165 out of 919 AGNs. The remaining physical parameters we provide are the bolometric luminosities and the Eddington ratios. A fraction of these AGNs have been observed by the OGLE survey since 1997 (all of them since 2001), enabling studies of correlations between the variability and physical parameters of these AGNs.
Abstract
We present the analyses of two microlensing events, OGLE-2018-BLG-0567 and OGLE-2018-BLG-0962. In both events, the short-lasting anomalies were densely and continuously covered by two ...high-cadence surveys. The light-curve modeling indicates that the anomalies are generated by source crossings over the planetary caustics induced by planetary companions to the hosts. The estimated planet/host separation (scaled to the angular Einstein radius
θ
E
) and mass ratio are (
s
,
q
× 10
3
) = (1.81 ± 0.02, 1.24 ± 0.07) and (
s
,
q
× 10
3
) = (1.25 ± 0.03, 2.38 ± 0.08), respectively. From Bayesian analyses, we estimate the host and planet masses as
(
M
h
,
M
p
)
=
(
0.25
−
0.13
+
0.27
M
⊙
,
0.32
−
0.17
+
0.34
M
J
)
and
(
M
h
,
M
p
)
=
(
0.54
−
0.28
+
0.33
M
⊙
,
1.34
−
0.70
+
0.82
M
J
)
, respectively. These planetary systems are located at a distance of
7.06
−
1.15
+
0.93
kpc
for OGLE-2018-BLG-0567 and
6.50
−
1.75
+
1.06
kpc
for OGLE-2018-BLG-0962, suggesting that they are likely to be near the Galactic bulge. The two events prove the capability of current high-cadence surveys for finding planets through the planetary-caustic channel. We find that most published planetary-caustic planets are found in Hollywood events in which the source size strongly contributes to the anomaly cross-section relative to the size of the caustic.
Aims.
With the aim of interpreting anomalous lensing events with no suggested models, we conducted a project of reinvestigating microlensing data collected in and before the 2019 season. In this ...work, we report a multi-planet system, OGLE-2019-BLG-0468L, that was found as a result of this project.
Methods.
The light curve of the lensing event OGLE-2019-BLG-0468, which consists of three distinctive anomaly features, could not be explained by the usual binary-lens or binary-source interpretations. We find a solution that explains all anomaly features with a triple-lens interpretation, in which the lens is composed of two planets and their host, making the lens the fourth multi-planet system securely found by microlensing.
Results.
The two planets have masses of ~3.4
M
J
and ~10.2
M
J
, and they are orbiting around a G-type star with a mass of ~0.9
M
⊙
and a distance of ~4.4 kpc. The host of the planets is most likely responsible for the light of the baseline object, although the possibility of the host being a companion to the baseline object cannot be ruled out.
Abstract
We present the analysis of seven microlensing planetary events with planet/host mass ratios
q
< 10
−4
: KMT-2017-BLG-1194, KMT-2017-BLG-0428, KMT-2019-BLG-1806, KMT-2017-BLG-1003, ...KMT-2019-BLG-1367, OGLE-2017-BLG-1806, and KMT-2016-BLG-1105. They were identified by applying the Korea Microlensing Telescope Network (KMTNet) AnomalyFinder algorithm to 2016–2019 KMTNet events. A Bayesian analysis indicates that all the lens systems consist of a cold super-Earth orbiting an M or K dwarf. Together with 17 previously published and three that will be published elsewhere, AnomalyFinder has found a total of 27 planets that have solutions with
q
< 10
−4
from 2016–2019 KMTNet events, which lays the foundation for the first statistical analysis of the planetary mass-ratio function based on KMTNet data. By reviewing the 27 planets, we find that the missing planetary caustics problem in the KMTNet planetary sample has been solved by AnomalyFinder. We also find a desert of high-magnification planetary signals (
A
≳ 65), and a follow-up project for KMTNet high-magnification events could detect at least two more
q
< 10
−4
planets per year and form an independent statistical sample.
Aims.
We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data.
Methods.
For this purpose, we conducted a systematic inspection of ...high-magnification microlensing events, with peak magnifications of
A
peak
≳ 30, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identified an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens.
Results.
We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close–wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is
q
~ 0.8 × 10
−4
for solution A and
q
~ 1.6 × 10
−4
for solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are (
M
p
,
M
h
,
D
L
) ~ (6.1
M
⊕
, 0.22
M
⊙
, 6.7 kpc) for solution A and ~(4.4
M
⊕
, 0.08
M
⊙
, 7.5 kpc) for solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar System’s ice giants, which were discovered by microlensing.
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