TY - JOUR
T1 - The mean number of extra microimage pairs for macrolensed quasars
AU - Granot, Jonathan
AU - Schechter, Paul L.
AU - Wambsganss, Joachim
PY - 2003/2/1
Y1 - 2003/2/1
N2 - When a gravitationally lensed source crosses a caustic, a pair of images is created or destroyed. We calculate the mean number of such pairs of microimages 〈n〉 for a given macroimage of a gravitationally lensed point source due to microlensing by the stars of the lensing galaxy. This quantity was calculated by Wambsganss, Witt, and Schneider in 1992 for the case of zero external shear, γ = 0, at the location of the macroimage. Since in realistic lens models a nonzero shear is expected to be induced by the lensing galaxy, we extend this calculation to a general value of γ. We find a complex behavior of 〈n〉 as a function of γ and the normalized surface mass density in stars, κ*. Specifically, we find that at high magnifications, where the average total magnification of the macroimage is 〈μ〉 = |(1 - κ*)2 - γ2|-1 ≫ 1, 〈n〉 becomes correspondingly large and is proportional to 〈μ〉. The ratio 〈n〉/〈μ〉 is largest near the line γ = 1 - κ*, where the magnification 〈μ〉 becomes infinite, and its maximal value is 0.306, We compare our semianalytic results for 〈n〉 with the results of numerical simulations and find good agreement. We find that the probability distribution for the number of extra microimage pairs is reasonably described by a Poisson distribution with a mean value of 〈n〉 and that the width of the macroimage magnification distribution tends to be largest for 〈n〉 ∼ 1.
AB - When a gravitationally lensed source crosses a caustic, a pair of images is created or destroyed. We calculate the mean number of such pairs of microimages 〈n〉 for a given macroimage of a gravitationally lensed point source due to microlensing by the stars of the lensing galaxy. This quantity was calculated by Wambsganss, Witt, and Schneider in 1992 for the case of zero external shear, γ = 0, at the location of the macroimage. Since in realistic lens models a nonzero shear is expected to be induced by the lensing galaxy, we extend this calculation to a general value of γ. We find a complex behavior of 〈n〉 as a function of γ and the normalized surface mass density in stars, κ*. Specifically, we find that at high magnifications, where the average total magnification of the macroimage is 〈μ〉 = |(1 - κ*)2 - γ2|-1 ≫ 1, 〈n〉 becomes correspondingly large and is proportional to 〈μ〉. The ratio 〈n〉/〈μ〉 is largest near the line γ = 1 - κ*, where the magnification 〈μ〉 becomes infinite, and its maximal value is 0.306, We compare our semianalytic results for 〈n〉 with the results of numerical simulations and find good agreement. We find that the probability distribution for the number of extra microimage pairs is reasonably described by a Poisson distribution with a mean value of 〈n〉 and that the width of the macroimage magnification distribution tends to be largest for 〈n〉 ∼ 1.
KW - Dark matter
KW - Gravitational lensing
KW - Quasars: general
UR - http://www.scopus.com/inward/record.url?scp=0041423805&partnerID=8YFLogxK
U2 - 10.1086/345447
DO - 10.1086/345447
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AN - SCOPUS:0041423805
SN - 0004-637X
VL - 583
SP - 575
EP - 583
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2 I
ER -