Can microlensing explain the long-term optical variability of quasars?

Free access article

Issue		A&A Volume 408, Number 1, September II 2003


Page(s)		17 - 25
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20030895

A&A 408, 17-25 (2003)
DOI: 10.1051/0004-6361:20030895

Can microlensing explain the long-term optical variability of quasars?

E. Zackrisson¹, N. Bergvall¹, T. Marquart¹ and P. Helbig²

¹ Department of Astronomy and Space Physics, Box 515, 75120 Uppsala, Sweden
² Multivax C&R, Friedrich-Ebert-Str. 83, 61118 Bad Vilbel, Germany

(Received 10 March 2003 / Accepted 6 June 2003)

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 $\Omega_\mathrm{M}=0.3$ , $\Omega_\Lambda=0.7$ 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 mag 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.

Key words: dark matter -- gravitational lensing -- quasars: general -- cosmology: miscellaneous

Offprint request: E. Zackrisson, ez@astro.uu.se

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