A Technical Review of Optical Gravitational Lensing Experiment/OGLE-IV

OGLE-IV: Fourth Phase of the Optical Gravitational Lensing Experiment

Authors:

Udalski et al

Abstract:

We present both the technical overview and main science drivers of the fourth phase of the Optical Gravitational Lensing Experiment (hereafter OGLE-IV). OGLE-IV is currently one of the largest sky variability surveys worldwide, targeting the densest stellar regions of the sky. The survey covers over 3000 square degrees in the sky and monitors regularly over a billion sources.

The main targets include the inner Galactic Bulge and the Magellanic System. Their photometry spans the range of 12 less than I less than 21 mag and 13 less than I less than 21.7 mag, respectively. Supplementary shallower Galaxy Variability Survey covers the extended Galactic bulge and 2/3 of the whole Galactic disk within the magnitude range of 10 less than I less than 19 mag. All OGLE-IV surveys provide photometry with milli-magnitude accuracy at the bright end. The cadence of observations varies from 19-60 minutes in the inner Galactic bulge to 1-3 days in the remaining Galactic bulge fields, Magellanic System and the Galactic disk.

OGLE-IV provides the astronomical community with a number of real time services. The Early Warning System (EWS) contains information on two thousand gravitational microlensing events being discovered in real time annually, the OGLE Transient Detection System (OTDS) delivers over 200 supernovae a year. We also provide the real time photometry of unpredictable variables such as optical counterparts to the X-ray sources and R CrB stars.

Hundreds of thousands new variable stars have already been discovered and classified by the OGLE survey. The number of new detections will be at least doubled during the current OGLE-IV phase. The survey was designed and optimized primarily to conduct the second generation microlensing survey for exoplanets. It has already contributed significantly to the increase of the discovery rate of microlensing exoplanets and free-floating planets.