X-Ray Astronomy Lab

1. X-Ray Astronomy Lab • X-rays • Why look for X-rays? • High temperatures • Atomic lines • Non-thermal processes • X-ray detectors • X-ray telescopes • The Lab

2. X-rays • Measure X-ray energies in energy units (eV or keV) or wavelength units (Angstroms) • Soft X-rays = 0.1-2 keV • Medium (“standard”) X-rays = 2-10 keV • Hard X-rays 20-200 keV

3. Photons Energy of photon is set by frequency/wavelength Unit is electon-volt (eV or keV) 1 eV = 1.610-19 J = 1.610-12 erg

4. Thermal Radiation Thermal spectrum peaks at 2.7 kT, falls off sharply at higher and lower energies. Wien’s Law: Peak of radiation = 2.9107Å/ T(K) = (0.43 keV) (T/106 K)

5. Black holes make X-rays • BH of 10 solar masses can have a luminosity of 100,000 times the Sun’s emitted from a region ~ 200 km in radius • Use Stefan-Boltzman law to find temperature, L = 4R2T4 TA = 1000  5700 K ~ 6,000,000 K Peak at 4.8 Å = 2.6 keV

6. Atomic lines Photons emitted from transitions to inner electron shells are in the X-ray band Link to tables of line energies

7. Non-thermal processes Particle acceleration in magnetic fields • Supernova remnants • Corona of black hole accretion disks • Radiation from pulsars • Jet acceleration by black holes

8. X-Ray Detectors • Usually detect each individual photon • Wish to measure photon properties • Energy • Number • Time of arrival • Position • Polarization

9. Solid State X-ray Detectors X-ray interacts in material to produce photoelectrons which are collected by applying a drift field

10. Energy Resolution Number of initial photoelectrons N = E/w, where E = energy of X-ray, w = average ionization energy (3.62 eV for Si) Creation of photoelectrons is a random process, number fluctuates Variance of N: N2 = FN, where F is the “Fano” factor, fluctuations are lower than expected from Poisson statistics (F = 0.17 for Ar, Xe) Energy resolution (FWHM) is For silicon, F = 0.115, w = 3.62 eV. Energy resolution is often degraded by electronic noise.

11. Quantum Efficiency To be detected, X-ray must pass through window without being absorbed and then be absorbed in gas Tw is geometric open fraction of window, t is window thickness, d is gas depth, ’s are absorption length for window/gas (energy dependent)

12. Charge Coupled Devices

13. Pixelated Detectors CCDs have small pixel sizes, good energy resolution, and a single readout electronics channel, but are slow, thin (< 300 microns), and only made in Si. Pixelated detectors have larger pixel sizes, require many electronics channels, but are fast and can be made thick and of various materials – therefore can be efficient up to higher energies

14. X-Ray Reflectivity

15. Grazing Incidence Optics

16. The Lab • Shine X-rays on sample • Measure energies of fluorescent X-rays • Determine elements in sample

17. X-Ray Generator Silicon X-Ray Detector

18. Setup X-ray source X Target X e- Multichannel analyzer Si Preamp 1. Calibrate MCA eV/channel: Measure spectra of known targets 2. Determine composition of unknown target: Measure spectrum and identify lines.