High Energy astrophysics started late in the history of modern astronomy, compared to other wavelength ranges, since it required the development of space flight through rockets and satellites.
Left: Spectral signature of monocromatic photons revealed by an ideal very large gamma-ray detector. Right: in real detectors the signal is the combination of all the different processes, and of the escaped energy.
Gas filled detectors work through photoionization of filling gas. Ionization potential is 10~30 eV (compared to 1~5 eV of solid state devices).
Depending on the applied voltage they work in different regimes (linear, saturated) and take different names (proportional counters, Geiger counters).
They work as seen for optical astronomy (cf. lecture of Prof. Brescia) but with some differences:
CCD in X-ray band thus give 4-dimensional arrays containing X,Y (or Ra,Dec), energy and time.
Grade selections allows to optimize the Signal to Noise ratio of an observations retaining only “significant” events: direct removal of cosmic rays and off-axis photons (from the XMM proposers manual).
CCD rely on photoelectric absorption of incident X-ray photons. Thus the probability of detecting a photon is approximately given by:
The resulting efficiency, expressed in terms of effective area, shows thee edges tipical of photoelectric absorption.
In designing a telescope you often want to place absorption edges of the detector within your energy range to increase the detection efficiency, while avoiding those of the mirrors. This is done through a proper choice of the building materials.
2. Absorption and scattering processes – Part I
3. Absorption and scattering processes – Part II
4. Emission processes – Part I
5. Emission processes – Part II
6. Instruments for X-ray and γ-ray Astrophysics – Part I
7. Instruments for X-ray and γ-ray Astrophysics – Part II
8. X-rays from the solar system
9. X-rays from low-mass and PMS stars
12. Evolution of Shell-type Supernova remnants
13. X-ray binaries
14. X-ray emission in normal galaxies
15. Active Galactic Nuclei – part I
16. Active Galactic Nuclei – Part II
17. Active Galactic Nuclei – Part III
18. Clusters of Galaxies – Part I
19. Clusters of Galaxies - Part II