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.

---

OGLE's EWS

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