Triggers:Microlensing

Standard events

Amplitude: can be many magnitudes, in range 0.1-10 mag.

Time-scale: is defined as Einstein Ring crossing time and is close to FWHM of the bell-like light curve of the event.

The light curves are usually symmetric with slow rise and slow decline. In case of high magnification, the rise in magnitude speeds up closer to the peak.

Sources: can be located anywhere, however, the further source, the higher chance of it being microlensed.

Exotic events

It is believed, around 10% of all events (at least towards the bulge) exhibit some kind of anomalous behaviour. In most cases it due to binary companion either to the source or the lens. The light curves are then usually asymmetric, with high amplification regions and sharp rises in magnitude in case of binary lenses.

Figure from Jaroszynski et al. 2004.

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OGLE's EWS

OGLE Early Warning System (EWS) is detecting in real-time about 600 events per year towards the Galactic bulge.

Distribution of time scales corrected for detection efficiency for OGLE-III Bulge events.

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All-sky events

99% of events are currently being detected towards the Galactic Centre, due to its largest optical depth. There is couple of events reported towards the Magellanic Cloud.

Serendipitous detection of a microlensing event located not in the crowded field: Gaudi et al. 2008

GSC 3656-1328

Light curve of GSC 3656-1328 microlensing event

Probability of all-sky microlensing (optical depth) in units of 10-8 for sources down to V=18 mag.

Estimated probability of all-sky microlensing, including lensing in the Bulge. Units 1e-8.

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Over 5 years of operation of Gaia, there should be around 3000 microlensing events occurring in the Bulge and about 750 over all sky.

Microlensing events detection efficiency by Gaia for events with time-scale of 15 days.

Microlensing events detection efficiency by Gaia for events with time-scale of 100 days.