“Worst-Case” Micro-Lensing in the Identification and Modeling of Lensed Quasars

Kavli Affiliate: Paul Schechter

| First 5 Authors: Luke Weisenbach, Paul Schechter, Sahil Pontula, ,

| Summary:

Although micro-lensing of macro-lensed quasars and supernovae provides unique
opportunities for several kinds of investigations, it can add unwanted and
sometimes substantial noise. While micro-lensing flux anomalies may be safely
ignored for some observations, they severely limit others. "Worst-case"
estimates can inform the decision whether or not to undertake an extensive
examination of micro-lensing scenarios. Here, we report "worst-case"
micro-lensing uncertainties for point sources lensed by singular isothermal
potentials, parameterized by a convergence equal to the shear and by the
stellar fraction. The results can be straightforwardly applied to
non-isothermal potentials utilizing the mass sheet degeneracy. We use
micro-lensing maps to compute fluctuations in image micro-magnifications and
estimate the stellar fraction at which the fluctuations are greatest for a
given convergence. We find that the worst-case fluctuations happen at a stellar
fraction $kappa_star=frac{1}{|mu_{macro}|}$. For macro-minima, fluctuations
in both magnification and demagnification appear to be bounded ($1.5>Delta
m>-1.3$, where $Delta m$ is magnitude relative to the average
macro-magnification). Magnifications for macro-saddles are bounded as well
($Delta m > -1.7$). In contrast, demagnifications for macro-saddles appear to
have unbounded fluctuations as $1/mu_{macro}rightarrow0$ and
$kappa_starrightarrow0$.

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