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We present the photometric analysis of Gaia19bld, a high-magnification($A\approx60$) microlensing event located in the southern Galactic plane, whichexhibited finite source and microlensing parallax effects. Due to a promptdetection by the Gaia satellite and the very high brightness of $I = 9.05~$magat the peak, it was possible to collect a complete and unique set ofmulti-channel follow-up observations, which allowed us to determine allparameters vital for the characterisation of the lens and the source in themicrolensing event. Gaia19bld was discovered by the Gaia satellite and wassubsequently intensively followed up with a network of ground-basedobservatories and the Spitzer Space Telescope. We collected multiplehigh-resolution spectra with Very Large Telescope (VLT)/X-Shooter tocharacterise the source star. The event was also observed with VLTInterferometer (VLTI)/PIONIER during the peak. Here we focus on the photometricobservations and model the light curve composed of data from Gaia, Spitzer, andmultiple optical, ground-based observatories. We find the best-fitting solutionwith parallax and finite source effects. We derived the limit on the luminosityof the lens based on the blended light model and spectroscopic distance. Wecompute the mass of the lens to be $1.13 \pm 0.03~M_{\odot}$ and derive itsdistance to be $5.52^{+0.35}_{-0.64}~\mathrm{kpc}$. The lens is likely a mainsequence star, however its true nature has yet to be verified by futurehigh-resolution observations. Our results are consistent with interferometricmeasurements of the angular Einstein radius, emphasising that interferometrycan be a new channel for determining the masses of objects that would otherwiseremain undetectable, including stellar-mass black holes.

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