Volume 420, Number 3, June IV 2004
|Page(s)||881 - 888|
|Published online||04 June 2004|
On the contribution of microlensing to X-ray variability of high-redshifted QSOs
National Astronomical Observatories, Chinese Academy of Sciences, 100012 Beijing, China
2 Institute of Theoretical and Experimental Physics, 25 B.Cheremushkinskaya st., Moscow 117259, Russia
3 Astro Space Centre of Lebedev Physics Institute, Moscow, Russia
4 Isaac Newton Institute of Chile, Moscow Branch, Russia
5 Astronomical Observatory, Volgina 7, 11160 Beograd, Serbia
6 Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
7 Isaac Newton Institute of Chile, Yugoslavia Branch, Yugoslavia
Corresponding author: L. Popović, firstname.lastname@example.org
Accepted: 10 March 2004
We consider a contribution of microlensing to the X-ray variability of high-redshifted QSOs. Such an effect could be caused by stellar mass objects (SMO) located in a bulge or/and in a halo of this quasar as well as at cosmological distances between an observer and a quasar. Here, we not consider microlensing caused by deflectors in our Galaxy since it is well-known from recent MACHO, EROS and OGLE observations that the corresponding optical depth for the Galactic halo and the Galactic bulge is lower than 10-6. Cosmologically distributed gravitational microlenses could be localized in galaxies (or even in bulge or halo of gravitational macrolenses) or could be distributed in a uniform way. We have analyzed both cases of such distributions. As a result of our analysis, we obtained that the optical depth for microlensing caused by stellar mass objects is usually small for quasar bulge and quasar halo gravitational microlens distributions (). On the other hand, the optical depth for gravitational microlensing caused by cosmologically distributed deflectors could be significant and could reach at . This means that cosmologically distributed deflectors may contribute significantlly to the X-ray variability of high-redshifted QSOs (). Considering that the upper limit of the optical depth () corresponds to the case where dark matter forms cosmologically distributed deflectors, observations of the X-ray variations of unlensed QSOs can be used for the estimation of the dark matter fraction of microlenses.
Key words: accretion, accretion disks / gravitational lensing / galaxies: quasars: general
© ESO, 2004
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