Constraining lens masses in moderately to highly magnified microlensing events from Gaia

¹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warsaw, Poland
² Astrophysics Division, National Centre for Nuclear Research, Pasteura 7, 02-093 Warsaw, Poland
³ Astronomical Institute, University of Wrocław, ul. Mikołaja Kopernika 11, 51-622 Wrocław, Poland
⁴ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University in Toruń, Grudziądzka 5, 87-100 Toruń, Poland
⁵ Faculty of Mathematics and Computer Science, Jagiellonian University, Łojasiewicza 6, 30-348 Kraków, Poland
⁶ Research School of Astronomy and Astrophysics, Australian National University, Mount Stromlo Observatory, Cotter Road Weston Creek, ACT, 2611 Canberra, Australia
⁷ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
⁸ Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, suite 102, Goleta, CA 93117, USA
⁹ Astronomical Observatory, Volgina 7, 11060 Belgrade, Serbia
¹⁰ E.Kharadze Georgian National Astrophysical Observatory, 0301 Abastumani, Georgia
¹¹ Janusz Gil Institute of Astronomy, University of Zielona Góra, Lubuska 2, PL-65-265 Zielona Góra, Poland
¹² Flarestar Obsevatory, Fl.5 Ent.B, Silver Jubilee Apt, George Tayar Street, San Gwann, SGN 3160, Malta
¹³ Horten Videregaende Skole, Strandpromenaden 33, 3183 Horten, Norway
¹⁴ Istanbul University, Faculty of Science, Department of Astronomy and Spaces Sciences, 34119, Istanbul Türkiye, Istanbul University Observatory Research and Application Center, Istanbul University, 34119 Istanbul, Türkiye
¹⁵ Department of Physics, Adıyaman University, Adıyaman 02040, Türkiye
¹⁶ Department of Physics, The George Washington University, Washington, DC 20052, USA
¹⁷ IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁸ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
¹⁹ INAF-Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, I-40129 Bologna, Italy
²⁰ Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio Av. 3, 10257 Vilnius, Lithuania
²¹ Astronomical Observatory, Jagiellonian University, ul. Orla 171, PL-30-244 Kraków, Poland
²² University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, NC 27599, USA
²³ Department of Astronomy, University of Virginia, 530 McCormick Rd., Charlottesville, VA 22904, USA
²⁴ School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland
²⁵ Université Ĉote d’Azur, Observatoire de la Ĉote d’Azur, CNRS, Laboratoire Lagrange, France
²⁶ Astronomical Institute of the Academy of Sciences of the Czech Republic (ASU CAS), 25165 Ondrejov, Czech Republic
²⁷ Faculty of Automatic Control, Electronics and Computer Science, Silesian University of Technology, Akademicka 16, 44-100 Gliwice, Poland
²⁸ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), Martí i Franquès 1, E-08028 Barcelona, Spain
²⁹ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), Martí i Franquès 1, E-08028 Barcelona, Spain
³⁰ Institut d’Estudis Espacials de Catalunya (IEEC), Esteve Terradas, 1, Edifici RDIT, Campus PMT-UPC, 08860 Castelldefels, (Barcelona), Spain
³¹ National Astronomical Research Institute of Thailand (Public Organization), 260 Moo 4, Donkaew, Mae Rim, Chiang Mai, 50180, Thailand
³² ICAMER Observatory of National Academy of Sciences of Ukraine, 27 Acad. Zabolotnoho str., Kyiv 03143, Ukraine
³³ Astronomy and Space Physics Department, Taras Shevchenko National University of Kyiv, 4 Glushkova ave., Kyiv 03022, Ukraine
³⁴ National Center “Junior Academy of Sciences of Ukraine”, 38-44 Dehtiarivska St., Kyiv 04119, Ukraine
³⁵ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
³⁶ Institute of Earth Systems, University of Malta, Msida, Malta
³⁷ Znith Astronomy Observatory, Naxxar, Malta
³⁸ University of St Andrews, Centre for Exoplanet Science, SUPA School of Physics & Astronomy, North Haugh, St Andrews KY16 9SS, United Kingdom
³⁹ Dipartimento di Fisica “E.R. Caianiello”, Università di Salerno, Via Giovanni Paolo II 132, I-84084 Fisciano, Italy
⁴⁰ Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Via Cintia, I-80126 Napoli, Italy
⁴¹ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, F-75014 Paris, France
⁴² Millennium Institute of Astrophysics MAS, Nuncio Monsenor Sotero Sanz 100, Of. 104, Providencia, Santiago, Chile
⁴³ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
⁴⁴ Leibniz-Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 1 April 2025
Accepted: 4 September 2025

Abstract

Context. Microlensing events provide a unique way to detect and measure the masses of isolated, non-luminous objects, particularly dark stellar remnants. Under certain conditions, it is possible to measure the mass of these objects using photometry alone, specifically when a microlensing light curve displays a finite source (FS) effect. This effect generally occurs in highly magnified light curves, i.e. when the source and the lens are very well aligned.

Aims. In this study, we analyse Gaia Alerts and Gaia Data Release 3 datasets, identifying four moderate-to-high-magnification microlensing events without a discernible FS effect. The absence of this effect suggests a large Einstein radius, implying substantial lens masses.

Methods. In each event, we constrained the FS effect, and therefore established lower limits for the angular Einstein radius and lens mass. Additionally, we used the DarkLensCode software to obtain the mass, distance, and brightness distribution for the lens based on the Galactic model.

Results. Our analysis established lower mass limits of ∼0.7 M_⊙ for one lens and ∼0.3 − 0.5 M_⊙ for two others. A DarkLensCode analysis supports these findings, estimating lens masses in the range of ∼0.42 − 1.70 M_⊙ and dark lens probabilities exceeding 80%. These results strongly indicate that the lenses are stellar remnants, such as white dwarfs or neutron stars.

Conclusions. While further investigations are required to confirm the nature of these lenses, we demonstrate a straightforward yet effective approach to identifying stellar remnant candidates.