The distortion of microlensing by mass distribution of our Galaxy
Abstract
We consider the distortion of standard gravitational microlens model by gravitational field of our Galaxy. We use the Chang  Refsdal lens for our analysis. The detailed discussions of the clear model is presented. We show that the influence of gravitational field of our Galaxy during microlensing may yield large variations of the stellar light curve although a probability of the phenomena is small. The microlensing effect was predicted by Byalko and Paczynsky. It is well known that a probability is too small ( ~10^{6}) to observe the effect, therefore one will take into account ( ~10^{6}) light curves to find that is microlensed. The first results of microlensing were published by MACHO and EROS collaborations. Now more than hundred microlensing events are known. But there are some problems in fitting of observational data by Schwarzschild microlens model. There are some approaches to solve the problems, for example, to consider nonvanishing size of source, binary system of source, two point mass gravitational lens ^{11)}, noncompact gravitational microlens. Using a very clear model of noncompact microlens a detailed analysis of microlensing was presented in papers. Similarly to Chang  Refsdal model, we consider the influence of Galactic mass distribution on microlensing effect us ing known Galactic model. Namely, we suppose that (rho_{G}(r) = rho_0 frac {{r_c}^2+{r_0}^2}{r^2+{r_0}^2},) where rho_G(r) is Galactic mass density, r_c is a distance from Galactic Center to Sun, (r_c = 8.5 kpc), rho_0 is Galactic mass density near Sun (rho_0 = 0.008 M_odot pc^{3}), r_0 in [2 kpc, 8 kpc]. If we suppose that a source is in LMC (D_s = 52 kpc), a gravitational microlens has a mass M = 0.1M_odot, and D_d = 10 kpc. If we suppose r_0 = 2 kpc, then we obtain for the axis size (in Einstein  Chwolson radius units) lambda = 1.6 times 10^{6}. If we suppose r_0 = 8 kpc, then we obtain for the axis size lambda = 2.5 times 10^{6}. We obtain also following expression for a critical curve X^{2} = 1 + lambda sin^2 phi, (where X  dimesionless vector in the lens plane) or X = 1 + frac {lambda sin^2 phi}{2} for small lambda Thus we obtain expression for caustic curve (Y_{1} =  lambda cos^3 phi, Y_{2} = lambda sin^3 phi) where (Y  dimensionless vector in the source plane). So, the critical curves are astroids. We obtained that caustic curves are astroids but an axis size is too small, therefore the probability to intersect a caustic curve is too small also but if a source inresects the caustic curve then a light curve displays great variations (there are two peaks of the stellar light curve), since a magnification increases very sharply near a fold singularity and more sharply near a cusp singularity. The work was supported in part by Russian Foundation for Basic Research (grant N 960217434).
 Publication:

Joint European and National Astronomical Meeting
 Pub Date:
 1997
 Bibcode:
 1997jena.confE.317Z