Math @ Duke

Publications [#243972] of Arlie O. Petters
Papers Published
 Gaudi, BS; Petters, AO, Gravitational microlensing near caustics. II. Cusps,
The Astrophysical Journal, vol. 580 no. 1 I
(2002),
pp. 468489, IOP Publishing, ISSN 0004637X [0206162v2], [doi]
(last updated on 2019/04/19)
Abstract: We present a rigorous, detailed study of the generic, quantitative properties of gravitational lensing near cusp catastrophes. Concentrating on the case in which the individual images are unresolved, we derive explicit formulas for the total magnification and centroid of the images created for sources outside, on, and inside the cusped caustic. We obtain new results on how the image magnifications scale with respect to separation from the cusped caustic for arbitrary source positions. Along the axis of symmetry of the cusp, the total magnification μ scales as μ α u1, where u is the distance of the source from the cusp, whereas perpendicular to this axis, μ α u2/3. When the source passes through a point u 0 on a fold arc abutting the cusp, the image centroid has a jump discontinuity; we present a formula for the size of the jump in terms of the local derivatives of the lens potential and show that the magnitude of the jump scales as u101/2 for u10 ≪ 1, where u10 is the horizontal distance between u0 and the cusp. The total magnifications for a small extended source located both on and perpendicular to the axis of symmetry are also derived, for both uniform and limbdarkened surface brightness profiles. We find that the difference in magnification between a finite and point source is ≲5% for separations of ≲2.5 source radii from the cusp point, while the effect of limb darkening is ≲1% in the same range. Our predictions for the astrometric and photometric behavior of both pointlike and finite sources passing near a cusp are illustrated and verified using numerical simulations of the cuspcrossing Galactic binary lens event MACHO1997BUL28. Our results can be applied to any microlensing system with cusp caustics, including Galactic binary lenses and quasar microlensing; we discuss several possible applications of our results to these topics.


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