1. Lecture 3
X-ray and gamma-ray satellites
Absorption in X-rays:
Photoelectric effect
Compton thickness

2. The Intergalactic medium Absorbs radiation: Lyman alpha forest
High-z QSO spectra (Becker et al. 2001)
The Intergalactic medium
Absorbs radiation:
Lyman alpha forest
And Lyman continuum
In high redshift quasars:
intervening absorption by
Clouds of neutral hydrogen

3. Equivalent width of Na I and K I lines and reddening A&A, 318, 269
Munari & Zwitter 1997:
Equivalent width of Na I and K I lines and reddening
A&A, 318, 269
Rauch 1998:
The Lyman-alpha forest in the spectra of QSOs
ARA&A, 36, 267

4. X-ray telescopes: grazing incidence

5. X-ray observations of Eta Carinae
Chandra XMM-Newton ASCA

6. M82 at high energies Chandra (0.5-8 keV) Fermi-LAT (>200 MeV)
VERITAS
(>700 GeV)

7. X-ray: keV
The history of X-ray astronomy started in the 1960s:
R. Giacconi 2003:
Nobel Lecture: The dawn of X-ray astronomy
Reviews of Modern Physics 75, 995
(see in particular launch of Italian X-ray satellite Uhuru in 1970)
In 40 years the X-ray flux sensitivity has improved by 10 orders of magnitudes, comparable to the improvement in optical instruments sensitivity in the last 400 years!
First high-energy baloon experiments: about e-08 erg/s/cm2
In 1-10 keV
Chandra (launched 1999): e-18 erg/s/cm2

8. Gamma-Rays: 100 keV - TeV Satellites: up to 300 GeV
Fermi Large Area Telescope (LAT)
Gamma-rays need solid state detectors:
Interaction of gamma-rays with matter converts the photon into an electron and positron pair. The path of the pair in the silicon strips allows arrival direction reconstruction. Their interaction with the calorimeter allows photon energy reconstruction

9. The Fermi GST mission: 11 June 2008
LAT
Glast Burst Monitor
Energy Range: 10 keV - 30 MeV
12 Sodium Iodide (NaI) Scintillation detectors
Burst trigger
Coverage of the typical GRB spectrum
(10 keV 1 MeV)
2 Bismuth Germanate (BGO) Scintillation detectors
Spectral overlap with the LAT
(150 keV-30 MeV)
Courtesy: N. Omodei

10. The AGILE satellite
Launched 23 April 2007

11. AGILE
SuperAGILE (18-60 keV)
GRID (30 MeV - 50 GeV)
Minicalorimeter
( MeV)

12. Neutral gas in our Galaxy absorbs thru photoelectric effect.
This is predominantly neutral hydrogen (HI): the Lyman limit
occurs at 912 Å = 13.6 eV
At frequencies higher than 13.6 eV part of the X-ray flux is
Absorbed, in a frequency-dependent way
Morrison & McCammon (1983, ApJ, 270, 119) have
computed this dependence in the keV energy
interval, taking into account cosmic abundances

15. Compton thick sources
In Seyfert 2 galaxies there is evidence of cold material around the nucleus and of absorption caused by this material in excess of the Galactic one. The local column density of this material is optically thick to Compton scattering
Bassani et al. 1999, ApJS, 121, 473
Matt et al. 1999, New Astronomy, 4, 191 (astro-ph/ )

16. Compton-thick sources