Conservation signals location

Astronomy & Astrophysics, 2021

Context. Microlensing provides a unique opportunity to detect non-luminous objects. In the rare cases that the Einstein radius θE and microlensing parallax πE can be measured, it is possible to determine the mass of the lens. With technological advances in both ground- and space-based observatories, astrometric and interferometric measurements are becoming viable, which can lead to the more routine determination of θE and, if the microlensing parallax is also measured, the mass of the lens. Aims. We present the photometric analysis of Gaia19bld, a high-magnification (A ≈ 60) microlensing event located in the southern Galactic plane, which exhibited finite source and microlensing parallax effects. Due to a prompt detection by the Gaia satellite and the very high brightness of I = 9.05 mag at the peak, it was possible to collect a complete and unique set of multi-channel follow-up observations, which allowed us to determine all parameters vital for the characterisation of the lens and...

2002

We present an re-analysis of the longest timescale gravitational microlensing event discovered to date: MACHO-99-BLG-22/OGLE-1999-BUL-32, which was discovered by both the MACHO and OGLE microlensing alert systems. Our analysis of this microlensing parallax event includes a likelihood analysis of the lens position based upon a standard model of the Galactic velocity distribution, and this implies that the lens could be

arXiv (Cornell University), 2023

We present the results of our analysis of Gaia19dke, an extraordinary microlensing event in the Cygnus constellation that was first spotted by the Gaia satellite. This event featured a strong microlensing parallax effect, which resulted in multiple peaks in the light curve. We conducted extensive photometric, spectroscopic, and high-resolution imaging follow-up observations to determine the mass and the nature of the invisible lensing object. Using the Milky Way priors on density and velocity of lenses, we found that the dark lens is likely to be located at a distance of D L = (3.05 +4.10 −2.42) kpc, and has a mass of M L = (0.51 +3.07 −0.40)M ⊙. Based on its low luminosity and mass, we propose that the lens in Gaia19dke event is an isolated white dwarf.

The Astrophysical Journal, 1997

We present analysis of MACHO Alert 95-30, a dramatic gravitational microlensing event towards the Galactic bulge whose peak magnification departs significantly from the standard point-source microlensing model. Alert 95-30 was observed in real-time by the Global Microlensing Alert Network (GMAN), which obtained densely sampled photometric and spectroscopic data throughout the event. We interpret the light-curve "fine structure" as indicating transit of the lens across the extended face of the source star. This signifies resolution of a star several kpc distant.

1994

The MACHO project is searching for dark matter in the form of massive compact halo objects (Machos), by monitoring the brightness of millions of stars in the Magellanic Clouds to search for gravitational microlensing events. Analysis of our first 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate microlensing events, well in excess of the ≈ 1 event expected from lensing by known low-mass stars. The event timescales range from 34 to 145 days, and the estimated optical depth is ∼ 2×10 −7 , about half of that expected from a 'standard' halo. Likelihood analysis indicates the typical lens mass is 0.5 +0.3 −0.2 M ⊙ , suggesting they may be old white dwarfs.

2001

We analyze PLANET photometric observations of the caustic-crossing binary-lens microlensing event, EROS BLG-2000-5, and find that modeling the observed light curve requires incorporation of the microlens parallax and the binary orbital motion. The projected Einstein radius (r E = 3.61 ± 0.11 AU) is derived from the measurement of the microlens parallax, and we are also able to infer the angular Einstein radius (θ E = 1.38 ± 0.12 mas) from the finite source effect on the light curve, combined with an estimate of the angular size of the source given by the source position in a color-magnitude diagram. The lens mass, M = 0.612 ± 0.057 M ⊙ , is found by combining these two quantities. This is the first time that parallax effects are detected for a caustic-crossing event and also the first time that the lens mass degeneracy has been completely broken through photometric monitoring alone. The combination ofr E and θ E also allows us to conclude that the lens lies in the near side of the disk, within 2.6 kpc of the Sun, while the radial velocity measurement indicates that the source is a Galactic bulge giant.

Nature, 2001

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.

The Astrophysical Journal, 2020

We report the lens mass and distance measurements of the nearby microlensing event TCP J05074264+2447555. We measure the microlens parallax vector π E using Spitzer and ground-based light curves with constraints on the direction of lens-source relative proper motion derived from Very Large Telescope Interferometer (VLTI) GRAVITY observations. Combining this π E determination with the angular Einstein radius θ E measured by VLTI GRAVITY observations, we find that the lens is a star with mass M = 0.495 ± 0.063 M at a distance D L = 429 ± 21 pc. We find that the blended light basically all comes from the lens. The lenssource proper motion is µ rel,hel = 26.55 ± 0.36 mas yr -1 , so with currently available adaptive-optics (AO) instruments, the lens and source can be resolved in 2021. This is the first microlensing event whose lens mass is unambiguously measured by interferometry + satellite parallax observations, which opens a new window for mass measurements of isolated objects such as stellar-mass black holes.

Astron Astrophys, 1998

For a given spatial distribution of the lenses and distribution of the transverse velocity of the lens relative to the line-of-sight, a probability distribution for the lens mass for a single observed event is derived. In addition, similar probability distributions are derived for the Einstein radius and the separation of the lens objects and their rotation period for a binary lens. These probability distributions are distinct from the distributions for the lens population, as investigated e.g. by the mass moment method of De Rújula et al. (1991). It is shown that the expectation value for the mass of a certain event as derived in this paper coincides with the estimated average mass of the underlying mass spectrum as found with the mass moment method when only one event is considered. The special cases of a Maxwellian velocity distribution and of a constant velocity are discussed in detail. For a rudimentary model of the Galactic halo, the probability distributions are shown and the relations between the expectation values of the physical quantities and the event timescale are given. For this model it is shown that within a 95.4 %-interval around the expectation value the mass varies by a factor of 800. For the observed events towards the LMC-including the binary lens models for MACHO LMC#1 (Dominik & Hirshfeld 1996) and MACHO LMC#9 (Bennett et al. 1996)-the results are shown explicitly. I discuss what information can be extracted and how additional information from the ongoing microlensing observations influences the results.