Issue |
A&A
Volume 420, Number 3, June IV 2004
|
|
---|---|---|
Page(s) | 881 - 888 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20034035 | |
Published online | 04 June 2004 |
On the contribution of microlensing to X-ray variability of high-redshifted QSOs
1
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, lpopovic@aip.de
Received:
2
July
2003
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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