POLAR

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POLAR SHARP-ASM

• Shuang Nan Zhang (???)
• Tsinghua University
• and
• Institute of High Energy Physics, Chinese Academy
  of Sciences

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Outlines

• POLAR a GRB Polarization Instrument aboard
  Chinas Spacelab to be launched around 2011-2012
• SHARP-ASM an instrument concept for an X-ray
  all-sky monitor with sub-arcsecond angular
  resolution and several eV energy resolution

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GRB prompt emission polarization one of the
last observables of GRBs

• Different GRB models
• E-M Model well defined, moderate Plin 50
• Fireball Model high values excluded Plin 10-20
  
• Cannon ball Model full range possible Plin 0 -
  100
• Probe quantum gravity (???)
• Amelino-Camelia G., 2000, Nature, 408, 661
• Amelino-Camelia G., et al., 1998, Nature, 393,
  763
• Piran T, 2005, Lect. Notes Phys, 669, 351
• Fan, Y-Z Wei, D-M Xu, D. 2007, MNRAS, 376, 1857

From M. Lyutikov, 2003
See papers discussing various GRB models T.
Piran, A. Dar, M. Lyutikov, D. Eichler, G.
Ghisellini, D. Lazzatti, M. Medvedev, E. Rossi
etc.
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Current GRB polarization measurements

• Polarization of the prompt ?-ray emission from
  the ?-ray burst of 6 December 2002 (RHESSI),
  Coburn, W Boggs, S. E., Nature, 2003, 423, 415
  (122 citations) Plin 80 20 (highly
  significant detection!)
• Re-analysis of polarization in the ?-ray flux of
  GRB 021206, Rutledge, R. E. Fox, D. B., MNRAS,
  2004, 350, 1288
• Statistical Uncertainty in the Re-Analysis of
  Polarization in GRB021206, Coburn, W
  Boggs, S. E., 2003astro.ph.10515B
• Gamma-Ray Burst Polarization Limits from RHESSI
  Measurements, Wiggler, C. et al, ApJ, 2004, 613,
  1088
• Evidence of polarisation in the prompt ?-ray
  emission from GRB 930131 and GRB 960924
  (BATSE/GRO), Willis, D. R. et al, 2005, AA, 439,
  245
• Polarisation studies of the prompt ?-ray emission
  from GRB 041219a using the spectrometer aboard
  INTEGRAL, McGlynn, S., 2007, AA, 466, 895

Important, rare, large uncertainty
controversial!
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POLAR mission status
POLAR

• Instrument concept proposed by N. Produit, et
  al., NIM (2005)
• Onboard Chinas spacelab TG-2 launch time
  2011-12
• FOV of POLAR ½ sky
• MDP is 10 gt10 GRBs per year down to 10
  polarization
• Requires directionality and energy spectrum known
  after the fact

Tian-Gong ?? Palace in Heaven
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The joint spacelab-TG POLAR team

• China Tsinghua/IHEP Shuang Nan Zhang (PI)
• China IHEP Bobing Wu, Shaolin Xiong, etc.
• Swizerland ISDC Nicolas Produit (Co-PI), Daniel
  Haas
• Switzerland PSI Wojtek Hajdas, Aliko
  Mchedlishvili
• Switzerland DPNC Estela Suarez, Martin Pohl,
  Catherine Leluc, Divic Rapin
• France LAPP Giovanni Lamanna, Jean-Pierre Vialle
• Poland IPJ Radoslaw Marcinkowski, Michal Gierlik

China 50 others 50
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Compton Scattering(F. LEI, A. J. DEAN and G. L.
HILLS,Space Science Reviews 82,309,1997)
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Azimuthal Scattering Angle
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Detector Models
PS bars 8x86mm6mm20cm PMT H8500 (88 anode
pixel)
Weight constraints lt 30 kg
PS Bars PMTs Weight (kg) Dimension (cm)
DM1 3232 44 12 2424
DM2 4040 55 20 3030
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Monte-Carlo Simulations
Direction Polarization Spectrum Band
(a-1.01,ß-3.31,Epeak390 keV) BATSE LogN-LogF
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Trigger Strategy

• For each event
• Ed (energy deposition) in every PS bar.
• Find the two bars of the highest energy
  deposition, i.e. Edmax, Edsec.
• Get the azimuthal scatter angle ?.

Find the optimum Trigger Strategy (TS) to reduce
the background rates. TS1 Edsec gt 5 keV the
total Ed lt 400 keV. TS2 TS1 and exclude the
adjacent hits. TS3 TS2 and the total Ed gt 30
keV.
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Effective Area Gamma-ray Energy
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Modulation factor Polarization Angle
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Modulation factor direction
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Comparison

• FOV 2pis better than FOV 1.3p
• 2) DM2 is better than DM1.

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Comparison
3)TS2 is better. Because it eliminates the
background induced by charged particles.
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Conclusion of simulations
With the 30 kg constraint, the best configuration
of POLAR is DM2
TS2 FOV 2p Detector Model 2
(40x40)(6mmx6mmx20cm) plastic scintillators
Trigger Strategy 2
Edsec gt 5 keV the total Ed lt 400 keV
exclude the adjacent
hits
Detector Model 2 PS Bars PMTs Weight (kg) Dimension (cm)
Detector Model 2 4040 55 20 3030
PS bar 6mm6mm20cm PMT H8500 (88 anode
pixel)
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POLAR capability summary
10 GRBs per year down to 8, or 60 GRBs per year
down to 30, or 100 GRBs per year down to 50
polarization, if all POLAR GRBs are localized
independently to degrees accuracy by other GRB
instruments.
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Feasibility studies ready for Phase-B
Vibration test survived
Polarizer in Switzerland
Polarization measured
Prototype in Switzerland
Eth5 keV achievable
Prototype in China
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Mechanical Design
Detector stack (outside)
Electronics box (inside)
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Sub-arcsecond X-ray ASM

• Current scheme in localizing GRBs
• ASM provides localization of arcmin
• Fast re-pointing of X-ray telescope for
  arcsecond positioning
• However no X-ray detection for a few percent of
  LGRBs and 1/4 SGRBs
• Nature of these GRBs?
• An ASM with sub-arcsecond angular resolution
  should be able to find out their host (or lack
  of) galaxies and their locations in their hosts
• Helpful in determining their nature?

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Super-High Angular Resolution Principle SHARP
Accepted for publication in Chinese Journal of A
A (arXiv0806.3494)
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Coded-mask imaging for geometrical optics
D
In principle, extremely fine angular resolution
may be achieved with very small D and very large L
L
Mask pattern
D
Shadow-gram
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Diffraction is not always negligible
For a pinhole of size 5 µm, the size of the
diffraction spot is 500 µm located at 2.5 m for 1
keV X-ray photons.
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X-ray diffraction simulation for a pinhole
1.24 keV
12.4 keV
Pixel and pinhole size 5 x 5 (µm)2 Pinhole to
detector distance 2.5 m
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Mask and Shadow-gram
Shadow-gram at 1.24 keV
Mask
Shadow-gram at 12.4 keV
Diffraction and interference between neighboring
holes dominate the observed shadow-gram
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traditional coded-mask cross-correlation image
of a point source in X-ray band
1.24 keV
12.4 keV
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DICC Diffraction/Interference Cross-Correlation

• traditional cross-correlation between the
  detected shadow-gram and the mask pattern
• In the limit of geometrical optics, a
  delta-function can be obtained for a point source
• DICC between the detected shadow-gram and the
  diffraction/interference pattern of
  multiple-pinholes of the mask for each energy
• For ideal detectors with absolute energy
  measurement for each photon, a delta-function can
  also be obtained for a point source

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DICC image of a point source in X-ray band
1.24 keV
12.4 keV
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Image comparison
1.24 keV
12.4 keV
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SHARP-ASM an instrument concept
Pixel size 5 x 5 (µm)2 Energy resolution 7
eV Energy range 0.2-12 keV Angular resolution lt
1 Location accuracy lt 0.1 FOV 60o x 60o
(with 36 modules) Technical challenge
cooling for such a huge TES array
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SHARP-ASM angular resolution
1.24 keV 0.72
12.4 keV 0.78
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SHARP comparisons
TES Cooling?
CCD CZT
36 modules
HETE-2 SXC (CCD) 0.5-14 keV, 0.91 sr, 3-15