Follow-up questions

Follow-up questions

Christoffer Lundman

KTH

January 27, 2011

Questions

1: Review possible sources for B(x, y), the signal independent noise. In practice, how might this be determined?

2: How can a refractive index be less than unity?

3: Explain how CdZnTe detectors work and compare to other detection techniques

4: Provide an overview of contemporary X-ray telescopes

1: Review possible sources for B(x, y), the signal independent noise. In practice, how might this be determined?

Sources of noise:

I

Diffuse X- / gamma-ray background

I

Cosmic rays

I

Neutrons (albedo / structure induced) As long as the noise is homogenous (approximately) over the detector plane, the image reconstruction algorithm won’t change.

D(x , y ) = A(x , y ) ∗ S (x , y ) + B(x , y )

2: How can a refractive index be less than unity?

I

Refractive index given by n ≡ c/v

, where v

is the phase velocity of the wave in the material

I

No information/energy travels with the phase velocity, thus it can be arbitrarily large

I

For phase velocity larger than c, n becomes less than unity

3: Explain how CdZnTe detectors work and compare to other detection techniques

I

Alloy of cadmium telluride &

zinc telluride

I

Direct bandgap semiconductor

I

High count rate in room temperature (> 10

photons/s/mm

)

I

High sensitivity for X- &

gammarays (high Z of cadmium and telluride)

I

Better energy resolution

than scintillator detectors

3: Explain how CdZnTe detectors work and compare to other detection techniques

I

Detector crystal metallized on top and botton (anode/cathode)

I

When hit by a photon, an electron/hole migrates to anode/cathode (photoelectric effect)

I

Depending on anode/cathode construction, positional information is read out

I

Directional information requires

other instrument parts (compton

scattering, coded mask)

3: Explain how CdZnTe detectors work and compare to other detection techniques

Semiconductors

I

Great energy (and spatial) resolution

I

May require cooling

Scintillators

I

Can be made into much

larger crystals, which means

a higher probability to

observe a given photon

4: Provide an overview of contemporary X-ray telescopes

Current X-ray missions:

I

AGILE

I

Chandra X-ray Observatory

I

Fermi

I

HETE-2

I

INTEGRAL

I

Rossi X-ray Timing Explorer

I

Suzaku

I

Swift

I

XMM-Newton Possible targets:

AGN, Galactic center, GRBs, SNR, Pulsars,

Dark matter..

4: Provide an overview of contemporary X-ray telescopes

Missions using Wolter type I focusing optics (nested mirrors):

Mission Instrument Energy range [keV]

Chandra ACIS 0.2-10

Suzaku XIS, XRS 0.4-10

Swift XRT 0.2-10

XMM-Newton EPIC, RGS 0.1-15

Common denominators:

I

Soft X-rays

I

Small FOV

I

Good imaging capabilities

4: Provide an overview of contemporary X-ray telescopes

Missions using coded masks:

Mission Instrument Energy range [keV]

AGILE Super-Agile 15-45

HETE-2 WFXM, SXC 2-25

INTEGRAL IBIS, SPI 15-10000

Swift BAT 10-150

Common denominators:

I

Hard X-rays

I

Large FOV

I

Good for catching transients

AGILE

HETE-2

Suzaku

Chandra

INTEGRAL

Swift

Fermi

RXTE

XMM-Newton