Microlensing Optical Depth and Event Rate in the OGLE-IV Galactic Plane Fields

Mróz, P.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Pietrukowicz, P.; Kozłowski, S.; Skowron, J.; Poleski, R.; Ulaczyk, K.; Gromadzki, M.; Rybicki, K.; Iwanek, Patryk; Wrona, Marcin

doi:10.3847/1538-4365/ab9366

Cited by 28 publications

(64 citation statements)

References 48 publications

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“…The Gaia19bld event lies in the OGLE-IV disc field GD1298.15, and was already reported by Mróz et al (2020) in the comprehensive statistical study of 630 microlensing events found by the OGLE project in the Galactic disc. OGLE provides a fairly complete light curve, because the cadence for this field was increased for the duration of the event from one per week to one per day.…”

Section: Ogle Datasupporting

confidence: 57%

Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc

Rybicki

Wyrzykowski

Bachelet

et al. 2021

A&A

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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 the source in the microlensing event. Methods. Gaia19bld was discovered by the Gaia satellite and was subsequently intensively followed up with a network of ground-based observatories and the Spitzer Space Telescope. We collected multiple high-resolution spectra with Very Large Telescope (VLT)/X-shooter to characterise the source star. The event was also observed with VLT Interferometer (VLTI)/PIONIER during the peak. Here we focus on the photometric observations and model the light curve composed of data from Gaia, Spitzer, and multiple optical, ground-based observatories. We find the best-fitting solution with parallax and finite source effects. We derived the limit on the luminosity of the lens based on the blended light model and spectroscopic distance. Results. We compute the mass of the lens to be 1.13 ± 0.03 M⊙ and derive its distance to be 5.52−0.64+0.35 kpc. The lens is likely a main sequence star, however its true nature has yet to be verified by future high-resolution observations. Our results are consistent with interferometric measurements of the angular Einstein radius, emphasising that interferometry can be a new channel for determining the masses of objects that would otherwise remain undetectable, including stellar-mass black holes.

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Section: Ogle Datasupporting

confidence: 57%

Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc

Rybicki

Wyrzykowski

Bachelet

et al. 2021

A&A

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“…This explains the sharp drop-off in long-duration events around this point. Mróz et al (2020a) conducted the largest Galactic plane search for microlensing events prior to this work, discovering 630 events in the OGLE survey observing 3000 square degrees of the Galactic plane between 2013 and 2019. ZTF Lam et al (2020) found that black holes could be identified by placing microlensing events in the t E -π E space and looking for the events with the largest t E and the shortest π E .…”

Section: Discussionmentioning

confidence: 99%

“…The Expérience pour la Recherche d'Objets Sombres (EROS) spiral arm surveys (Rahal et al 2009) observed 12.9 million stars across four directions in the Galactic plane and discovered 27 microlensing events over seven years between 1996 and 2002. The Optical Gravitational Lensing Experiment (OGLE; Mróz et al (2020a)) discovered 630 events in 3000 square degrees of Galactic plane fields in the 7 years between 2013 and 2019. They measured a threefold increase in the average Einstein crossing time for Galactic plane events as compared to the Galactic bulge and an asymmetric optical depth that they interpret as evidence of the Galactic warp.…”

mentioning

confidence: 99%

60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One

Medford¹,

Lu²,

Nugent³

et al. 2022

Preprint

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Microlensing events have historically been discovered throughout the Galactic bulge and plane by surveys designed solely for that purpose. We conduct the first multi-year search for microlensing events on the Zwicky Transient Facility (ZTF), an all-sky optical synoptic survey that observes the entire visible Northern sky every few nights. We discover 128 high quality microlensing events in the three years of ZTF-I using the bulk lightcurves in the ZTF Public Data Release 5. We find an excess of longduration Galactic plane events when comparing our results to both previous surveys and simulations. 35 of our events are found outside of the Galactic plane (|b| ≥ 15 • ), nearly tripling the number of previously discovered events in the stellar halo from surveys pointed toward the Magellanic Clouds and the Andromeda Galaxy. We also record 1690 ongoing candidate events as potential microlensing that can continue to be observed by ZTF-II for identification. The scalable and computationally efficient methods developed in this work can be applied to future synoptic surveys such as the Rubin Observatory's Legacy Survey of Space and Time and the Nancy Grace Roman Space Telescope as they attempt to find microlensing events in even larger and deeper datasets.

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“…Such an effect, combined with a large timescale t E can be used to constrain the mass of the lens and to find microlensing dark remnants candidates (Poindexter et al 2005;Wyrzykowski et al 2016;Wyrzykowski & Mandel 2020;Lam et al 2020;Karolinski & Zhu 2020;Abrams & Takada 2020;Mróz & Wyrzykowski 2021). The longest ever detected microlensing event had a timescale of 640 +68 −54 days (Mao et al 2002) and only a few known events have timescales around 400 days (Wyrzykowski et al 2015;Mróz et al 2020). Terrestrial parallax occurs when a microlensing event is observed from two separate observatories on Earth.…”

Section: Introductionmentioning

confidence: 99%

Lens parameters for Gaia18cbf -- a long gravitational microlensing event in the Galactic plane

Kruszyńska,

Wyrzykowski,

Rybicki

et al. 2021

Preprint

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Context. The size of the Einstein Radius in a microlensing event scales as a square root of the mass of the lens. Therefore, long-lasting microlensing events are the best 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 has exhibited a long timescale and features characteristic to 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 investigate the range of microlensing models and use 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 star. Results. This event is one of the longest ever detected, with the Einstein timescale of t E = 491.41 +128.31 −84.94 days for the best solution and t E = 453.74 +178.69 −105.74 days for the second-best. This translates to a lens mass of M L = 2.91 +6.02 −1.70 M and M L = 1.88 +4.40 −1.19 M respectively. The limits on the blended light suggest that this event was most likely not caused by a main sequence star, but rather by a dark remnant of stellar evolution.

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Microlensing Optical Depth and Event Rate in the OGLE-IV Galactic Plane Fields

Cited by 28 publications

References 48 publications

Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc

Single-lens mass measurement in the high-magnification microlensing event Gaia19bld located in the Galactic disc

60 Microlensing Events from the Three Years of Zwicky Transient Facility Phase One

Lens parameters for Gaia18cbf -- a long gravitational microlensing event in the Galactic plane

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