Can Microlensing Explain the Long-Term Optical Variability of Quasars?

Abstract

Although controversial, the scenario of microlensing as the dominant mechanism for the long-term optical variability of quasars does provide a natural explanation for both the statistical symmetry, achromaticity and lack of cosmological time dilation in quasar light curves. Here, we investigate to what extent dark matter populations of compact objects allowed in the currently favored Omega_M=0.3, Omega_Lambda=0.7 cosmology really can explain the quantitative statistical features of the observed variability. We find that microlensing reasonably well reproduces the average structure function of quasars, but fails to explain both the high fraction of objects with amplitudes higher than 0.35 magnitudes and the mean amplitudes observed at redshifts below one. Even though microlensing may still contribute to the long-term optical variability at some level, another significant mechanism must also be involved. This severely complicates the task of using light-curve statistics from quasars which are not multiply imaged to isolate properties of any cosmologically significant population of compact objects which may in fact be present.

9 pages, 7 figures, accepted for publication in A&A

References in corpus (12)

• The 2dF QSO Redshift Survey - I. The Optical QSO Luminosity Function
• Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?
• EROS and MACHO Combined Limits on Planetary Mass Dark Matter in the Galactic Halo
• The Dipole Observed in the COBE DMR Four-Year Data
• Variability in active galactic nuclei: confrontation of models with observations
• Time Dilation and Quasar Variability
• Quasar variability: correlations with amplitude
• On the Probability Distribution of Cosmological Microlensing Optical Depths
• The Dyer-Roeder distance-redshift relation in inhomogeneous universes
• The Signature of Microlensing in QSO Variability-Redshift Correlations
• The Cloudy Universe
• Constraining the Cosmological Density of Compact Objects with the Long-Term Variability of Quasars

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• Ensemble Variability of Near-Infrared-Selected Active Galactic Nuclei
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• Detecting compact dark matter in galaxy clusters via gravitational microlensing: A2218 & A370
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• Free-floating "planets'' in the macrolensed quasar Q2237+0305
• Microlensing in phase space II: Correlations analysis
• Supernovae Light Curves: An Argument for a New Distance Modulus