Chapitres
- Multiple
Quasars
- Quasar
Microlensing: Theory
- Quasar
Microlensing: Observations and
Results
- Quasar
Microlensing: Simulations
Résumé
About
one in 1000 quasars is multiply
imaged by an intervening galaxy or
cluster of galaxies. Stars
in the lensing galaxies can
act as "microlenses". We
can detect this microlensing
effect as a time-variable
magnification of the background
quasar, due to the relative motion
between quasar, galaxy and
Earth. (This has to be
distinguished from intrinsic
quasar variability!). Amplitude
and shape of this variability
depend on the size of the quasar
and the density and nature of the
lensing objects. Hence
microlensing can be used to
explore both aspects: Size and
structure of the innermost
part of the quasar engine, as
well as the (possibly dark)
microlenses. After
introducing the concept and
the possibilities of quasar
microlensing, some
observational results will
be presented.
In the last part of the talk, the
technique how to calculate quasar
microlensing
("backward ray
tracing") will be
described: We simulate
the light deflection by tracing
light rays backward from the
observer on Earth through a
field of randomly positioned
stellar-mass lenses and
calculating their
deflections. The resulting
two-dimensional maps in the
"quasar plane" indicate the
density of light rays by different
colors, it is the
magnification of the
background quasar as a function of
its position.
The sharp "caustic lines" in the
map are locations of very
high magnification. When a
background quasar moves across
such a pattern, we can
determine its variable brightness.
By comparison with
observational results from
monitoring (macro-)lensed
quasars, we can deduce the
size and brightness profile of
the quasar. |
Bibliographie
- Quasar
Microlensing
Schmidt, R. W.
and Wambsganss, Joachim,
General Relativity and Gravitation,
Volume 42, Issue 9, pp.2127-2150,
adsabs.harvard.edu/abs/2010GReGr..42.2127S
- Gravitational
Microlensing
Wambsganss,
Joachim, (from: 33rd Saas-Fee
Advanced Course: "Gravitational
Lensing: Strong, Weak and Micro",
arxiv.org/abs/astro-ph/0604278
|
