Gravitational Binary-Lens Events with Prominent Effects of Lens Orbital Motion (original) (raw)
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The Astrophysical Journal, 2011
We present the analysis result of a gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by 2 adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling of the light curve considering the parallax effect and Keplerian orbital motion, we are able to measure not only the physical parameters but also a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance 6.7 ± 0.3 kpc from the Earth. The individual lens components with masses 0.9±0.3 M ⊙ and 0.5±0.1 M ⊙ are separated with a semi-major axis of a = 2.5 ± 1.0 AU and orbiting each other with a period P = 3.1 ± 1.3 yr. The event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.
The binary gravitational lens and its extreme cases
Astronomy and Astrophysics, 1999
The transition of the binary gravitational lens from the equal mass case to small (planetary) mass ratios q is studied. It is shown how the limit of a (pure shear) Chang-Refsdal lens is approached, under what conditions the Chang-Refsdal approximation is valid, and how the 3 different topologies of the critical curves and caustics for a binary lens are mapped onto the 2 different topologies for a Chang-Refsdal lens with pure shear. It is shown that for wide binaries, the lensing in the vicinity of both lens objects can be described by a Taylorexpansion of the deflection term due to the other object, where the Chang-Refsdal approximation corresponds to a truncation of this series. For close binaries, only the vicinity of the secondary, less massive, object can be described in this way. However, for image distances much larger than the separation of the lens objects, any binary lens can be approximated by means of multipole expansion, where the first non-trivial term is the quadrupole term. It is shown that an ambiguity exists between wide and close binary lenses, where the shear at one of the objects due to the other object for the wide binary is equal to the absolute value of the eigenvalues of the quadrupole moment for the close binary. This analysis provides the basis for a classification of binary lens microlensing events, especially of planetary events, and an understanding of present ambiguities.
The Astrophysical Journal
We analyze the gravitational binary-lensing event OGLE-2016-BLG-0156, for which the lensing light curve displays pronounced deviations induced by microlens-parallax effects. The light curve exhibits 3 distinctive widely-separated peaks and we find that the multiple-peak feature provides a very tight constraint on the microlens-parallax effect, enabling us to precisely measure the microlens parallax π E. All the peaks are densely and continuously covered from high-cadence survey observations using globally located telescopes and the analysis of the peaks leads to the precise measurement of the angular Einstein radius θ E. From the combination of the measured π E and θ E , we determine the physical parameters of the lens. It is found that the lens is a binary composed of two M dwarfs with masses M 1 = 0.18 ± 0.01 M ⊙ and M 2 = 0.16 ± 0.01 M ⊙ located at a distance D L = 1.35 ± 0.09 kpc. According to the estimated lens mass and distance, the flux from the lens comprises an important fraction, ∼ 25%, of the blended flux. The bright nature of the lens combined with the high relative lens-source motion, µ = 6.94 ± 0.50 mas yr −1 , suggests that the lens can be directly observed from future high-resolution follow-up observations.
Astrophysical Journal, 2001
We present the photometry and theoretical models for a Galactic bulge microlensing event OGLE-2000-BUL-43. The event is very bright with I = 13.54 mag, and has a very long time scale, t E = 156 days. The long time scale and its light curve deviation from the standard shape strongly suggest that it may be affected by the parallax effect. We show that OGLE-2000-BUL-43 is the first discovered microlensing event, in which the parallax distortion is observed over a period of 2 years. Difference Image Analysis (DIA) using the PSF matching algorithm of Alard & Lupton enabled photometry accurate to 0.5%. All photometry obtained with DIA is available electronically. Our analysis indicates that the viewing condition from a location near Jupiter will be optimal and can lead to magnifications ∼ 50 around January 31, 2001. These features offer a great promise for resolving the source (a K giant) and breaking the degeneracy between the lens parameters including the mass of the lens, if the event is observed with the imaging camera on the Cassini space probe. Subject headings: gravitational microlensing -stars: individual OGLE-2000-BUL-43 * Based on observations obtained with the 1.3 m Warsaw Telescope at the Las Campanas Observatory of the Carnegie Institution of Washington.
Full characterization of binary-lens event OGLE-2002-BLG-069 from PLANET observations
2005
We analyze the photometric data obtained by PLANET and OGLE on the caustic-crossing binary-lens microlensing event OGLE-2002-BLG-069. Thanks to the excellent photometric and spectroscopic coverage of the event, we are able to constrain the lens model up to the known ambiguity between close and wide binary lenses. The detection of annual parallax in combination with measurements of extended-source effects allows us to determine the mass, distance and velocity of the lens components for the competing models. While the model involving a close binary lens leads to a Bulge-Disc lens scenario with a lens mass of M = (0.51 ± 0.15) M⊙ and distance of DL = (2.9 ± 0.4) kpc, the wide binary lens solution requires a rather implausible binary black-hole lens (M 126 M⊙). Furthermore we compare current state-of-the-art numerical and empirical models for the surface brightness profile of the source, a G5III Bulge giant. We find that a linear limb-darkening model for the atmosphere of the source star is consistent with the data whereas a PHOENIX atmosphere model assuming LTE and with no free parameter does not match our observations.
The Astrophysical Journal, 2016
Light curves of microlensing events involving stellar binaries and planetary systems can provide information about the orbital elements of the system due to orbital modulations of the caustic structure. Accurately measuring the orbit in either the stellar or planetary case requires detailed modeling of subtle deviations in the light curve. At the same time, the natural, Cartesian parameterization of a microlensing binary is partially degenerate with the microlens parallax. Hence, it is desirable to perform independent tests of the predictions of microlens orbit models using radial velocity time series of the lens binary system. To this end, we present 3.5 years of RV monitoring of the binary lens system OGLE-2009-BLG-020L, for which Skowron et al. (2011) constrained all internal parameters of the 200-700 day orbit. Our RV measurements reveal an orbit that is consistent with the predictions of the microlens light curve analysis, thereby providing the first confirmation of orbital elements inferred from microlensing events.
KMT-2019-BLG-1715: Planetary Microlensing Event with Three Lens Masses and Two Source Stars
The Astronomical Journal, 2021
We investigate the gravitational microlensing event KMT-2019-BLG-1715, the light curve of which shows two short-term anomalies from a caustic-crossing binary-lensing light curve: one with a large deviation and the other with a small deviation. We identify five pairs of solutions, in which the anomalies are explained by adding an extra lens or source component in addition to the base binary-lens model. We resolve the degeneracies by applying a method in which the measured flux ratio between the first and second source stars is compared with the flux ratio deduced from the ratio of the source radii. Applying this method leaves a single pair of viable solutions, in both of which the major anomaly is generated by a planetary-mass third body of the lens, and the minor anomaly is generated by a faint second source. A Bayesian analysis indicates that the lens comprises three masses: a planet-mass object with ∼2.6 M J and binary stars of K and M dwarfs lying in the galactic disk. We point o...
Theoretical Aspects of Gravitational Lensing in T e V e S
The Astrophysical Journal, 2006
Since creation of his Tensor-Vector-Scalar theory (TeVe S), the Modified Newtonian dynamics (MOND) paradigm has been redeemed from the embarrassment of lacking a relativistic version. One primary success of TeVe S is that it provides an enhancement of gravitational lensing, which could not be achieved by other MONDian theories. Following Bekenstein's work, we investigate the phenomena of gravitational lensing including deflection angles, lens equations and time delay. We find that the deflection angle would maintain its value while the distance of closest approach vary in the MOND regime. We also use the deflection angle law to derive magnification and investigate microlensing light curves. We find that the difference in the magnification of the two images in the point mass model is not a constant such as in GR. Besides, microlensing light curves could deviate significantly from GR in the deep MOND regime. Furthermore, the scalar field, which is introduced to enhance the deflection angle in TeVe S, contributes a negative effect on the potential time delay. Unfortunately this phenomenon is unmeasurable in lensing systems where we can only observe the time delay between two images for a given source. However, this measurable time delay offers another constraint on the mass ratio of the dark matter and MOND scenarios, which in general differs from that given by the deflection angle. In other words, for a lensing system, if two masses, m gN and m gM , are mutually alternatives for the deflection angles in their own paradigm, regarding the time delay they are in general in an exclusive relation.