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

¹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
e-mail: krybicki@astrouw.edu.pl
² Las Cumbres Observatory, 6740 Cortona Drive, Suite 102, Goleta, CA 93117, USA
³ Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 75014 Paris, France
⁴ Max Planck Institute for Astronomy, Konigstuhl 17, 69117 Heidelberg, Germany
⁵ Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
⁶ IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁷ Center for Astrophysics, Harvard & Smithsonian, 60 Garden St, MS-15 Cambridge, MA 02138, USA
⁸ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁹ Astronomical Institute, University of Wrocław, ul. Kopernika 11, 51-622 Wrocław, Poland
¹⁰ ROAD Observatory, San Pedro de Atacama, Chile
¹¹ Vereniging Voor Sterrenkunde (VVS), Oostmeers 122 C, 8000 Brugge, Belgium
¹² Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
¹³ Dept. of Physics and Astronomy, University College London, Gower St., London WC1E 6BT, UK
¹⁴ National Astronomical Research Institute of Thailand, 260 Moo 4, Donkaew, Mae Rim, Chiang Mai 50180, Thailand
¹⁵ Data Science Research Center, Department of Statistics, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
¹⁶ Faulkes Telescope Project, School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA Wales, UK
¹⁷ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
¹⁸ Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copayapu 485, Copiapó, Chile
¹⁹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
²⁰ Kavli Institute for Cosmology Cambridge, Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
²¹ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
²² Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²³ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12-14, 69120 Heidelberg, Germany
²⁴ University of St Andrews, College Gate, St Andrews KY16 9AJ, UK
²⁵ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot, 76100, Israel
²⁶ Physics Department and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
²⁷ Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
²⁸ Auckland Observatory, Auckland, New Zealand
²⁹ Kumeu Observatory, Kumeu, New Zealand
³⁰ Farm Cove Observatory, Centre for Backyard Astrophysics, Pakuranga, Auckland, New Zealand
³¹ Klein Karoo Observatory, Centre for Backyard Astrophysics, Calitzdorp, South Africa
³² Institute for Radio Astronomy and Space Research (IRASR), AUT University, Auckland, New Zealand
³³ Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland
³⁴ Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio al. 3, Vilnius 10257, Lithuania

Received: 28 September 2020
Accepted: 20 July 2021

Abstract

Context. Microlensing provides a unique opportunity to detect non-luminous objects. In the rare cases that the Einstein radius θ_E and microlensing parallax π_E 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 θ_E 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.