DETECTION LEVEL ENHANCEMENTS OF GRAVITATIONAL MICROLENSING EVENTS FROM LIGHT CURVES: THE SIMULATIONS

Microlensing can be seen as a version of strong gravitation lensing where the separation angle of theimage formed by light deection by a massive object is too small to be seen by a ground based opticaltelescope. As a result, what can be observed is the change in light intensity as function of time; the lightcurve. Conventionally, the intensity of the source is expressed in magnitudes, which uses a logarithmicfunction of the apparent ux, known as the Pogson formulae. In this work, we compare the magnitudesfrom the Pogson formulae with magnitudes from the Asinh formulae (Lupton et al. 1999). We foundfor small uxes, Asinh magnitudes give smaller deviations, about 0.01 magnitudes smalller than Pogsonmagnitudes. This result is expected to give signi cant improvement in detection level of microlensinglight curves.Key words: gravitational lensing: micro; methods: data analysis1. INTRODUCTIONA research group which routinely provides early indica-tion of the occurrence of gravitational microlensing isthe Optical Gravitational Lensing Experiment (OGLE)group. This group built an early warning detection sys-tem for gravitational microlensing events and providephotometrically reduced data Udalski (1994). In gen-eral, the brightness of an astronomical object is de nedby its apparent ux (hereafter referred to as ux). Theux is converted into apparent brightness using the Pog-son formulae for magnitude (m). We know very well howthe Pogson formulae works, and it gives reliable magni-tude errors for large uxes. Conversely, for a small ux,with low S/N, the error in the magnitude will be verylarge. Therefore, Lupton et al. (1999) proposed a newset of equations to de ne object magnitudes, using theInverse Hyperbolic Sine function (hereafter referred toas Asinh magnitude) that works well in low the S/Nregime.2. OBJECTIVES AND METHODOLOGYWe want to determine whether Asinh magnitudes cangive better results in terms of the errors of magnitudesfor small uxes. Later, we want to increase the detectionlevel of gravitational microlensing from light curves byusing Asinh magnitudes. For the initial work, we per-http://pkas.kas.orgformed a simulated magnitude calculation from inputssuch as the temperature range, size, and distance of thesource. In this work, we use stellar radii in the range1-3 R and star temperatures between 3000{11000 K,corresponding to stars of spectral classes A to M, andobservations at visual wavelengths of (= 550 nm). Inaddition, we also adopt one value for source distance,d= 8.5 kpc. Magnitudes from the simulations will beconverted to Asinh magnitudes. Later, we apply Asinhmagnitudes to OGLE photometric reduced data withmagnitudes brighter than 19m, selected using the Mi-crolens Priority Generator from RoboNet Planet Searchfor the 2013 and 2014 seasons. The photometric datafrom the Early Warning System OGLE (EWS-OGLE)does not provide ux information. Therefore, we usedthe transformation equations from Bessel et al. (1998),to calculate the ux and its error.3. DATAWe choose one microgravitational lensing event for eachseason, with input parameters of the Las Campanas Ob-servatory ˚= 29