Free-Floating planet Mass Function from MOA-II 9-year survey towards the Galactic Bulge

We present the first measurement of the mass function of free-floating planets (FFP) or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006-2014. Six events are likely to be due to planets with Einstein radius crossing times, $t_{\rm E}<0.5$days, and the shortest has $t_{\rm E} = 0.057\pm 0.016$days and an angular Einstein radius of $\theta_{\rm E} = 0.90\pm 0.14\mu$as. We measure the detection efficiency depending on both $t_{\rm E}$ and $\theta_{\rm E}$ with image level simulations for the first time. These short events are well modeled by a power-law mass function, $dN_4/d\log M = (2.18^{+0.52}_{-1.40})\times (M/8\,M_\oplus)^{-\alpha_4}$ dex$^{-1}$star$^{-1}$ with $\alpha_4 = 0.96^{+0.47}_{-0.27}$ for $M/M_\odot < 0.02$. This implies a total of $f= 21^{+23}_{-13}$ FFP or very wide orbit planets of mass $0.33<M/M_\oplus < 6660$ per star, with a total mass of $80^{+73}_{-47} M_\oplus$ per star. The number of FFPs is $19_{-13}^{+23}$ times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of $\alpha\sim 0.9$, which would imply a total mass of $171_{-52}^{+80} M_\oplus$ star$^{-1}$. This model predicts that Roman Space Telescope will detect $988^{+1848}_{-566}$ FFPs with masses down to that of Mars (including $575^{+1733}_{ -424}$ with $0.1 \le M/M_\oplus \le 1$). The Sumi(2011) large Jupiter-mass FFP population is excluded.Comment: 17 pages, 7 figures, accepted for publication in A

Brown dwarf companions in binaries detected from the 2021 season high-cadence microlensing surveys

As a part of the project aiming to build a homogeneous sample of binary-lens (2L1S) events containing brown-dwarf (BD) companions, we investigate the 2021 season microlensing data collected by the Korea Microlensing Telescope Network (KMTNet) survey. For this purpose, we first identify 2L1S events by conducting systematic analyses of anomalous lensing events. We then select candidate BD-companion events by applying the criterion that the mass ratio between the lens components is less than $q_{\rm th}\sim 0.1$. From this procedure, we find four binary-lens events including KMT-2021-BLG-0588, KMT-2021-BLG-1110, KMT-2021-BLG-1643, and KMT-2021-BLG-1770, for which the estimated mass ratios are $q\sim 0.10$, 0.07, 0.08, and 0.15, respectively. The event KMT-2021-BLG-1770 is selected as a candidate despite the fact that the mass ratio is slightly greater than $q_{\rm th}$ because the lens mass expected from the measured short time scale of the event, $t_{\rm E}\sim 7.6$~days, is small. From the Bayesian analyses, we estimate that the primary and companion masses are $(M_1/M_\odot, M_2/M_\odot)= (0.54^{+0.31}_{-0.24}, 0.053^{+0.031}_{-0.023})$ for KMT-2021-BLG-0588L, $(0.74^{+0.27}_{-0.35}, 0.055^{+0.020}_{-0.026})$ for KMT-2021-BLG-1110L, $(0.73^{+0.24}_{-0.17}, 0.061^{+0.020}_{-0.014})$ for KMT-2021-BLG-1643L, and $(0.13^{+0.18}_{-0.07}, 0.020^{+0.028}_{-0.011})$ for KMT-2021-BLG-1770L. It is estimated that the probabilities of the lens companions being in the BD mass range are 82\%, 85\%, 91\%, and 59\% for the individual events. For confirming the BD nature of the lens companions found in this and previous works by directly imaging the lenses from future high-resolution adaptive-optics (AO) followup observations, we provide the lens-source separations expected in 2030, which is an approximate year of the first AO light on 30~m class telescopes.Comment: 11 pages, 10 tables, 8 figure

KMT-2021-BLG-1150Lb: Microlensing planet detected through a densely covered planetary-caustic signal

Recently, there have been reports of various types of degeneracies in the interpretation of planetary signals induced by planetary caustics. In this work, we check whether such degeneracies persist in the case of well-covered signals by analyzing the lensing event KMT-2021-BLG-1150, for which the light curve exhibits a densely and continuously covered short-term anomaly. In order to identify degenerate solutions, we thoroughly investigate the parameter space by conducting dense grid searches for the lensing parameters. We then check the severity of the degeneracy among the identified solutions. We identify a pair of planetary solutions resulting from the well-known inner-outer degeneracy, and find that interpreting the anomaly is not subject to any degeneracy other than the inner-outer degeneracy. The measured parameters of the planet separation (normalized to the Einstein radius) and mass ratio between the lens components are $(s, q)_{\rm in}\sim (1.297, 1.10\times 10^{-3})$ for the inner solution and $(s, q)_{\rm out}\sim (1.242, 1.15\times 10^{-3})$ for the outer solution. According to a Bayesian estimation, the lens is a planetary system consisting of a planet with a mass $M_{\rm p}=0.88^{+0.38}_{-0.36}~M_{\rm J}$ and its host with a mass $M_{\rm h}=0.73^{+0.32}_{-0.30}~M_\odot$ lying toward the Galactic center at a distance $D_{\rm L} =3.8^{+1.3}_{-1.2}$~kpc. By conducting analyses using mock data sets prepared to mimic those obtained with data gaps and under various observational cadences, it is found that gaps in data can result in various degenerate solutions, while the observational cadence does not pose a serious degeneracy problem as long as the anomaly feature can be delineated.Comment: 9 pages, 8 figure

KMT-2021-BLG-1547Lb: Giant microlensing planet detected through a signal deformed by source binarity

We investigate the previous microlensing data collected by the KMTNet survey in search of anomalous events for which no precise interpretations of the anomalies have been suggested. From this investigation, we find that the anomaly in the lensing light curve of the event KMT-2021-BLG-1547 is approximately described by a binary-lens (2L1S) model with a lens possessing a giant planet, but the model leaves unexplained residuals. We investigate the origin of the residuals by testing more sophisticated models that include either an extra lens component (3L1S model) or an extra source star (2L2S model) to the 2L1S configuration of the lens system. From these analyses, we find that the residuals from the 2L1S model originate from the existence of a faint companion to the source. The 2L2S solution substantially reduces the residuals and improves the model fit by $\Delta\chi^2=67.1$ with respect to the 2L1S solution. The 3L1S solution also improves the fit, but its fit is worse than that of the 2L2S solution by $\Delta\chi^2=24.7$. According to the 2L2S solution, the lens of the event is a planetary system with planet and host masses $(M_{\rm p}/M_{\rm J}, M_{\rm h}/M_\odot)=\left( 1.47^{+0.64}_{-0.77}, 0.72^{+0.32}_{-0.38}\right)$ lying at a distance \D_{\rm L} =5.07^{+0.98}_{-1.50}~kpc, and the source is a binary composed of a subgiant primary of a late G or an early K spectral type and a main-sequence companion of a K spectral type. The event demonstrates the need of sophisticated modeling for unexplained anomalies for the construction of a complete microlensing planet sample.Comment: 9 pages, 4 tables, 7 figure

KMT-2022-BLG-0440Lb: A New q<10−4q < 10^{-4} Microlensing Planet with the Central-Resonant Caustic Degeneracy Broken

We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, $q = 0.75$--$1.00 \times 10^{-4}$ at $1\sigma$. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by $\Delta\chi^2 > 70$. The binary-source model can fit the anomaly well but is rejected by the ``color argument'' on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disk, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9^{+0.6}_{-0.7}$ or $4.6^{+1.4}_{-1.7}$ au, subject to the close/wide degeneracy. This is the third $q < 10^{-4}$ planet from a high-magnification planetary signal ($A \gtrsim 65$). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability in detecting high-magnification planetary signals for $q < 10^{-4}$ planets, which are challenging for the current microlensing surveys.Comment: MNRAS accepte

Systematic KMTNet Planetary Anomaly Search. IX. Complete Sample of 2016 Prime-Field Planets

As a part of the ``Systematic KMTNet Planetary Anomaly Search" series, we report five new planets (namely, OGLE-2016-BLG-1635Lb, MOA-2016-BLG-532Lb, KMT-2016-BLG-0625Lb, OGLE-2016-BLG-1850Lb, and KMT-2016-BLG-1751Lb) and one planet candidate (KMT-2016-BLG-1855), which were found by searching $2016$ KMTNet prime fields. These $buried$ planets show a wide range of masses from Earth--class to Super--Jupiter--class, and are located in both the disk and the bulge. The ultimate goal of this series is to build a complete planet sample. Because our work provides a complementary sample to other planet detection methods, which have different detection sensitivities, our complete sample will help us to obtain a better understanding of planet demographics in our Galaxy.Comment: 38 pages, 17 figures, 12 Tables, submitted to the AAS journa

OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters arising from a Five Day Xallarap Effect in a Candidate Planetary Microlensing Event

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves $\chi^2$ values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters like mass-ratio, $q$, and separation, $s$, cannot be constrained well. However, we also find that the parameters for the source system like the orbital period and semi major axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of $P\sim5$ days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.Comment: 19 pages, 7 figures, 6 tables. Accepted by A

Transmission Control Considering Different Available Channels for CRDSA/IRSA in Satellite IoT Systems

In satellite Internet-of-Things (IoT) systems using the 920-MHz band Low Power Wide Area, available channels for each terminal are limited to avoid interference with terrestrial networks. Since this limitation depends on the location of the terminal, the available channels are different, resulting in throughput degradation. This paper proposes a transmission control scheme that reduces throughput degradation due to different available channels in the Contention Resolution Diversity Slotted ALOHA (CRDSA)/Irregular-Repetition Slotted ALOHA (IRSA) system. The proposed transmission control uses constraints that consider the characteristics of CRDSA/IRSA, as well as an objective function that considers fairness of throughput among terminals. Under these constraints and objective function, the transmission probability was calculated using an objective function that maximized the transmitting load. The computer simulation showed that it could achieve high throughput by preventing the influence of difference in the available channels

Free-floating Planet Mass Function from MOA-II 9 yr Survey toward the Galactic Bulge

We present the first measurement of the mass function of free-floating planets (FFPs), or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006–2014. Six events are likely to be due to planets with Einstein radius crossing times t _E < 0.5 days, and the shortest has t _E = 0.057 ± 0.016 days and an angular Einstein radius of θ _E = 0.90 ± 0.14 μ as. We measure the detection efficiency depending on both t _E and θ _E with image-level simulations for the first time. These short events are well modeled by a power-law mass function, ${{dN}}_{4}/d\mathrm{log}M={({2.18}_{-1.40}^{+0.52})\times (M/8\,{M}_{\oplus })}^{-{\alpha }_{4}}$ dex ^−1 star ^−1 with ${\alpha }_{4}={0.96}_{-0.27}^{+0.47}$ for M / M _⊙ < 0.02. This implies a total of $f={21}_{-13}^{+23}$ FFPs or very wide orbit planets of mass 0.33 < M / M _⊕ < 6660 per star, with a total mass of ${80}_{-47}^{+73}{M}_{\oplus }$ star ^−1 . The number of FFPs is ${19}_{-13}^{+23}$ times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α ∼ 0.9, which would imply a total mass of ${171}_{-52}^{+80}{M}_{\oplus }$ star ^−1 . This model predicts that Roman Space Telescope will detect ${988}_{-566}^{+1848}$ FFPs with masses down to that of Mars (including ${575}_{-424}^{+1733}$ with 0.1 ≤ M / M _⊕ ≤ 1). The Sumi et al. large Jupiter-mass FFP population is excluded