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gaia data release 3 documentation

10.9 Microlensing

10.9.3 Calibration models

Microlensing events change the observed brightness sometimes by orders of magnitude. In the process of recognising Microlensing events using the goodness of model fit, it is important to use the measurement uncertainties, which may reflect a scatter across a wide range of magnitudes. We wanted to use the reduced χ2 in the evaluation of the best fitting model, but we noticed that the original σGgdr3 lead to reduced χ21 for genuine microlensing events. So we rescaled the uncertainties on G magnitudes to match the expected scatter in Gaia DR3 data. We used Gaia DR3 mean G vs its standard deviation to derive the expected lowest possible uncertainty σGexp for each G measurement, assuming 30 observations on average per object, using the following formulae:

σGexp={30×100.17×13.5-5.1forG<13.5mag30×100.17×G-5.1forG13.5mag, (10.11)

which is added in quadrature to the Gaia DR3 uncertainty σGgdr3 for estimating the employed value σGnew:

σGnew=(σGgdr3)2+(σGexp)2. (10.12)

The GBP and GRP data often contained outliers; therefore, in order to avoid incorrect Microlensing model to be driven by those outliers, we rescaled uncertainties in GBP and GRP time series by a constant factor of 10. This enforced GBP and GRP data points to have negligible contribution to the Microlensing model.