MEASURES AND OBSERVATIONS OF CELESTIAL X AND GAMMA RAYS
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- Versione italiana
- Academic year
- 2022/2023
- Teacher
- FILIPPO FRONTERA
- Credits
- 6
- Didactic period
- Secondo Semestre
- SSD
- FIS/01
Training objectives
- Goal of the course is that of providing to the master student advanced knowledge of experimental X- and gamma-ray astronomy, in particular its theoretical grounds.With this knowledges, the student is capable to to design an X-ray telescope with the desired features, and he is capable to evaluate its expectations, eg. sensitivity and angular resolution, and optimize them.
Prerequisites
- Basic knowledgde of optics, quantum mechanics, relativity and structure of the matter.
Course programme
- Information that can be extracted from the detection of the electromagnetic radiation of celestial origin. (2 hrs).
Detection of electromagnetic radiation: principles. Photoelectric effect and its applications. Thomson scattering. Compton effect and its applications. Pair production. Criteria for the choice of the detector material. Proportional counters, scintillator detectors, solid state detectors. Expected photon spectra. Consequences of secondary interactions. (13 hrs)
Observational limits. Angular resolution limit. Basic concepts of interferometry. Detection limits to the continuum intensity and to X-ray lines for direct-viewing telescopes and focusing telescopes. Detection limits to flux temporal variations. (6 hrs)
High energy gamma-ray telescopes (>20 MeV). Principles and instrument configurations flown. Cerenkov radiation for very high energy gamma-rays. Compton Telescopes for medium gamma-ray energies (300 keV - 20 MeV). Sky direct-viewing X-/soft gamma-ray telescopes. Mechanical collimators. Modulation collimators and rotating modulating collimators (only hints). (6 hrs)
Coded mask systems: operation principle. Introduction to convolution, its applications and properties. Comparison between convolution and cross correlation. Image formation through a mask. Mask image deconvolution. Angular resolution of a mask system. Accuracy in locating a point source. Mask configurations. Signal to noise ratio of the reconstructed image. (10 hrs)
X-ray reflection: operation principles. Theory of total external reflection for grazing incidence. Measurement of the refraction index. X-ray reflection from real surfaces. Geometries of the focusing optics. Parabolic configuration. Wolter I telescope geometry. Oblique aberrations. Abbe condition. Kirkpatrick-Baez telescope. Kumakhov lenses. “Lobster eye” telescopes. One-dimensional Schmidt imagers. Schmidt telescopes for two-dimensional imaging. (10 hrs)
Bragg diffraction and its applications to hard X/soft gamma-ray telescopes. Perfect, mosaic and curved crystals. Reflectivity of flat mosaic crystals for Laue configuration. Reflectivity of curved crystals in Laue configuration. Multilayer mirrors and supermirrors. Laue lens design. Optical properties of a lens. (6 hrs)
Introduction to X-ray detectors. Basic diagram of a detector. Pulse height amplitude spectrum. Energy resolution and spectroscopic resolving power. Detection efficiency. Dead time. Pile up. (5 hrs)
Spectral deconvolution. Hypothesis test. Application to X-ray telescopes. (2 hrs) Didactic methods
- Online Lectures.
Learning assessment procedures
- Exercises during the course. Oral exam, in which, in addition to understand if the student has acquired the theoretical knowledges of experimental X-/gamma.ray astrophysics, he is invited to face various problematics, which are typical of the experimental X-/gamma-ray astrophysics, like the design of an X-/gamma-ray detector or telescope with given requirements, or establishing the type of instrument or technology required to measure specific high energy astrophysics quantities.
Reference texts
- G. B. Rybicki and A. P. Lightman, Radiative processes in astrophysics, John Wiley and Sons.
R. C. Smith, Observational Astrophysics, Cambridge University Press.
G. E. Knoll, Radiation Detection and Measurements, John Wiley and Sons.
Lecture notes prepared by the lecturer
