Microlens mass determination for Gaia's predicted photometric events


Type
Article
Change log
Authors
McGill, P 
Smith, LC 
Evans, NW 
Zhang, ZH 
Abstract

We used Gaia Data Release 2 to search for upcoming photometric microlensing events, identifying two candidates with high amplification. In the case of candidate 1, a spectrum of the lens (l1) confirms it is a usdM3 subdwarf with mass ≈0.11M, while the event reaches maximum amplification of 20−10+20 mmag on November 3rd 2019 ($\pm$1d). For candidate 2, the lens (l2) is a metal-poor M dwarf with mass ≈0.38M derived from spectral energy distribution (SED) fitting, and maximum amplification of 10−10+40 mmag occurs on June 3rd 2019 ($\pm$4d). This permits a new algorithm for mass inference on the microlens. Given the predicted time, the photometric lightcurve of these events can be densely sampled by ground-based telescopes. The lightcurve is a function of the unknown lens mass, together with 8 other parameters for all of which Gaia provides measurements and uncertainties. Leveraging this prior information on the source and lens provided by Gaia's astrometric solution, and assuming that a ground-based campaign can provide 50 measurements at mmag precision, we show for example that the mass of l1 can be recovered to within 20 per cent (68 per cent confidence limit).

Description
Keywords
gravitational lensing: micro, stars: low-mass, subdwarfs
Journal Title
Monthly Notices of the Royal Astronomical Society
Conference Name
Journal ISSN
0035-8711
1365-2966
Volume Title
483
Publisher
Oxford University Press (OUP)
Rights
Publisher's own licence
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)
STFC (1950369)