Geant4 Simulation of PoGO on the reduced design

1
Geant4 Simulation of PoGO on the reduced design

• January 20, 2003
• Tsunefumi Mizuno, H. Tajima and T. Kamae
• mizuno_at_SLAC.Stanford.EDU

2
Simulated Geometry

• Thickness of fast scint. 2.63cm
• (D 2.23cm)
• W (thickness of slow scint.) 0.2cm
• L1 (slow scint. length) 60cm
• L2 (fast scint. length) 20cm
• Thickness of W collimator 0.0025cm
• Thickness of btm BGO 2.68cm
• Length of btm BGO 3cm
• (not tapered in simulator for simplicity)
• Gap between BGOs 0.5cm
• (including BaSo4 eflector)
• Thickness of side Anti BGO 3cm
• Length of side Anti BGO 60cm
• of units 397 (geometrical area of fast scint.
  not covered by slow scint. 1709cm2) or 217
  (934.4 cm2)

Simulation of realistic geometry
3
Simulation Condition

• The same spectrum as that used in Hiros EGS4
  simulation
• E-2.1 spectrum with 100mCrab intensity, 20-200keV
  (300.8 c/s/m2)
• 6h exposure, attenuation by air of 3g/cm2
• Use Geant4 ver5.1. Possible minor bug of
  polarization vector after scattering was fixed by
  user (found and fixed by Y. Fukazawa _at_ Hiroshima
  Univ.).
• Assumed detector response
• 0.5 photo-electron/keV
• fluctuated by poission distribution and smeared
  by gaussian of sigma0.5 keV
• minimum hit threshold is 3 keV for both fast and
  veto scintillators.
• Event selection
• 2 or 3 hits in fast scintillators
• The largest energy deposit is considered to be
  photo absorption and the second largest to be
  compton scattering.

4
EGS4 results (for reference)
EGS4 MC prediction
polarization profiles of three models
Definitions of P1/P2/IP
5
G4 results for 397 units

• Fit the azimuth angle distribution with
  p0(1p1cos(2(phi-p2)pi))

Crab Pulsar PolarizationP1
Crab Pulsar PolarizationP2
p20.273-0.035 (polar cap model) p21.62-0.07
(caustic model) p2-0.33-0.06 (outer cap model)
Polar Cap Model Caustic Model Outer Cap Model
MF3.14-0.46

• Modulation can be detected by 7 sigma or more
• We can distinguish models by 10 sigma or more
  (difference of the phase)

We confirmed the EGS4 results with G4 simulation.
6
G4 results for 217 units

• Fit the azimuth angle distribution with
  p0(1p1cos(2(phi-p2)pi))

Crab Pulsar PolarizationP1
Crab Pulsar PolarizationP2
p20.342-0.045 (polar cap model) p21.54-0.10
(caustic model) p2-0.22-0.10 (outer cap model)
Polar Cap Model Caustic Model Outer Cap Model
MF3.10-0.65

• Modulation can be detected by 5 sigma or more
• We can distinguish models by 6 sigma or more
  (difference of the phase)

Even the PoGO of reduced design allows us to
distinguish three models in 6-hour observation.