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XMM - advanced
X-ray Astronomy
school
I. Georgantopoulos
NATIONAL OBSERVATORY OF ATHENS
Talks Overview
[AGN are mainly addressed]
Overview XMM
Formation of jets in AGN (Vlahakis)
X-ray emission from jets (Mastichiadis)
Radio quiet AGN, I, II (Corral)
Scripts for data analysis (Ranalli)
XMM data analysis, the SAS package (Corral)
X-ray spectra and XSPEC (Corral)
The 3XMM source catalog
X-rays: an Introduction
X-rays :
60 Angstrom or Ε = h v
keV
0.2keV up to 100
The most energetic phenomenae in the Universe
Temperatures 1-100 million degrees
High temperatures because of large gravitational potentials
(black holes and clusters of galaxies).
Contents
Brief History of X-ray Astronomy
Instrumentation and the X-ray missions
Capabilities XMM
The first X-ray observations
1949 Sun
(solar corona, gas 106 K)
SOHO
image of the sun.This is not a 1949 observation
!!
Why observe in X-rays ?
WIEN’s LAW
Wavelength inversely prop.
Temperature
λmax= 3x107 / T

Energetic phenomenae, temperatures of
million degrees (very large gravitational
potentials: BH, clusters of galaxies)
Birth of X-ray astronomy
1962. Trying to observe the moon.
Not detected instead
Sco-X1 and the X-ray background
Giacconi
(Nobel 2003)
1962 measurement
X-ray Moon as pictured by rosat in 1990
1960
1970
1979/1990
1993
1999
First X-ray satellite UHURU (1970), First imaging Einstein (1979), First imaging of hard
X-rays (2-10 keV) ASCA (1993)
XMM
XMM has 3 telescopes.
The first telescope focuses the light on the PN
CCD detector.
In the other two telescopes the light is split
between the MOS CCD detectors and the RGS
grating spectrograph.
XMM components
The 3
Telescopes
Detectors
X-ray Telescopes
-- Wolter type telescopes
where the X-rays are
scaterred on two
tubes.
Nested tubes to increase the telescope area
Grazing angle
Max grazing angle:
θc ∝ E-1 √Z
Spatial Resolution
The XMM spatial resolution is 16 arcsec Half-Power-Diameter
(this is the light from a point source will be spread in (almost) a
Gaussian with the above dimensions).
Although the spatial resolution in all telescopes is dictated by
Airy’s law which says that for a given telescope diameter, the
resolution (decreases) gets better with decreasing wavelength.
However, two effects play a crucial role in X-rays:
a) micro-roughness (how well are the mirrors polished)
b) the mirror alignments
Telescope Area
compare with Keck 785.000 cm2 (160 larger)
An example of an X-ray image
Limitations:
XMM view of the tycho SNR
1.
PSF degrades off-axis
2.
Vignetting
3.
Background
Sensitivity
We detect sources down to a given signal-to-noise ratio (SNR)
SNR= S x t / SQRT (BKG x t )
Hence the flux limit goes with the square root of the exposure time:
In the above:
t= exposure time
S= source counts per sec
BKG= background counts (noise) per sec
Sensitivity: spatial resolution
The sensitivity has to do with the spatial resolution
of the telescope and secondly with the size of the telescope
Signal-to-noise ratio = Net counts / SQRT
(BKG)
Chandra: 50% light in 1 arcsec
XMM
50% light 16arcsec
background (BKG) in XMM 256 larger SQRT
(256)= 16 tikes fainter
More on XMM optics
The size of the PSF increases with increasing off-axis angle. This effect is energy
dependent.
X-ray detectors: CCD
Do not give only images but also low resolution spectra
( ΔE/E~ 6 % spectral resolution
ONLY for moderately bright sources)
The idea is that the more the energetic the photon the more
the electrons that are produced
Works if there are not many photons ( 1/ 3sec)
Otherwise pile-up
(a situation in which no spectra can be obtained)
data cubes (event files)
4-dimensions
x-y (Image)
Energy (spectrum)
Time (Light curve)
More complex requests eg image 2-4 keV, Light
curve 6-7 keV
CCD spectra
why a black hole ?
Spectroscopy/Gratings
Grating spectroscopy
(λ/Δλ~1000)
Chandra vs. XMM
Chandra (NASA)
XMM (ESA)
a. 5000 cm2 @ 1keV
(largest
telescope)
b. moderate spatial resolution 6
arcsec FWHM
c. CCDs
d. Gratings at low energies
a. Highest spatial resolution ever
achieved 1 arcsec (~optical
astronomy)
b. 1000 cm2
c. CCDs
d. Grating at both high and low
energies
Bibliography
‘X-ray spectroscopy in Astrophysics’ (van Paradijs, Bleeker eds)
Springer
‘The Universe in X-rays’ (Truemper et al. eds) Springer
Exploring the X-ray Universe, ‘Cambridge Univ. Press’, Seward