Letter to the Editor

A possible nearby microlensing stellar remnant hiding in Gaia DR3 astrometry

¹ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
e-mail: majajjablonska@gmail.com
² Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
³ Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK

Received: 1 August 2022
Accepted: 22 September 2022

Abstract

Massive galactic lenses with large Einstein Radii should cause a measurable astrometric microlensing effect, that is, a light centroid shift due to the motion of the two images. Such a shift in the position of a background star due to microlensing was not included in the Gaia astrometric model, and therefore significant deviation should cause Gaia’s astrometric parameters to be determined incorrectly. Here we study one of the photometric microlensing events reported in the Gaia Data Release 3, GaiaDR3-ULENS-001, for which a poor goodness of Gaia fit and erroneous parallax could indicate the presence of an astrometric microlensing signal. Based on the photometric microlensing model, we simulated Gaia astrometric time series with the astrometric microlensing effect added. We find that including microlensing with an angular Einstein radius of θ_E = 2.60_−0.24^+0.21 mas (2.47_−0.24^+0.28 mas) assuming a positive (negative) impact parameter, u₀, reproduces the astrometric quantities reported by Gaia well. We estimate the mass of the lens to be 1.00_−0.18^+0.23 M_⊙ (0.70_−0.13^+0.17  M_⊙) and its distance 0.90_−0.11^+0.14 kpc (0.69_−0.09^+0.13 kpc), proposing the lens could be a nearby isolated white dwarf.