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PoGO: Hard X-ray Polarimeter for GLAST Mission

This presentation provides an overview of the PoGO (Polarized Gamma-ray Observer) mission and its collaboration with the GLAST mission. It discusses the hardware developments, scientific targets, and progress in X-ray astrophysics, emphasizing the importance of polarization measurements in understanding high-energy objects such as pulsars and accretion disks. The unique features of PoGO, including its extremely high sensitivity and narrow field of view, are highlighted. The presentation also outlines the collaboration and schedule of the mission, including balloon flights and beam tests.

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PoGO: Hard X-ray Polarimeter for GLAST Mission

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  1. Hard X-ray Polarimeter PoGO and GLAST mission (硬X線偏光観測PoGO計画とGLASTとの連携) • November 25, 2005, GLAST Science Workshop at Titech • Tsunefumi Mizuno (Hiroshima University) for the PoGO Collaboration • mizuno@hirax6.hepl.hiroshima-u.ac.jp • Outline: • Introduction • PoGO mission • Hardware Developments • Scientific Targets

  2. Progress of X-ray Astrophysics Energy Resolution at 5.9 keV Point Spread Funciton Einstein (IPC) Uhuru Tenma (SPC) ASCA (SIS) Einstein (IPC) ROSAT (PSPC) Chandra (ACIS) Chandra (HEG) Suzaku (XRS) Sensitivity • In X-ray Astrophysics, the imaging capability, spectral resolving power and point source sensitivity have improved by orders of magnitude. However, … Uhuru Einstein (IPC) Chandra (ACIS)

  3. (Little) Progress of Polarization Measurement Crab Nebula Polarization measurement with OSO-8 (1976) Modulation curve for 2.6 keV Crab Nebula signal+BG BG Intensity of the source from which pol. was detected • Two carbon Bragg diffraction polarimeters • @2.6 keV and 5.2 keV • 19.2+-1.0 % polarization from Crab Nebula (Weisskopf et al. 1976) • Signal/BG ratio was ~9(2.6 keV)/2(5.2 keV) • No significant (3s) pol. detection from Crab pulsar Results has not been surpassed for ~30 years, but PoGO (Polarized Gamma-ray Observer) can do!

  4. What can polarization tell us about HE objects? • --- Processes known to polarize hard X-rays --- • Synchrotron emission: pol. vector is perpendicular to magnetic field and can tell us the direction of the field. • SNRs, Pulsars, AGN jets, micro-quasars and GRBs • Compton Scattering: pol. vector is perpendicular to the plane of scattering and can tell us the geometry of the photon source and the scatterer (e.g., accretion disk) • BH binaries, Seyfert AGNs • Propagation of photons in strong magnetic field: photons with pol. vector perpendicular to magnetic field are highly absorbed. Good for the test of quantum electrodynamics and reconstruction of the direction of the magnetic field. • Isolated pulsars, NS binaries with a strong cyclotron line. • Polarization is a powerful tool for the direct measurement of source geometry.

  5. Concept of the Compton Polarimeter Utilize azimuthal angle asymmetry of Compton Scattering to measure hard X-ray polarization Klein-Nishina cross section pol. vector Azimuthal angle distribution 90degree scattering is the best for the polarization measurement 0 degree 45 degree Modulation Factor is defined as 135 degree 90 degree

  6. Polarized Gamma-ray Observer (PoGO) • Utilize well-type phoswich counter design: plastic scintillators (main detector) shielded by slow scintillators (active collimator) and side/bottom BGO. Similar to Suzaku HXD-II. • Energy band is 30-100 keV: Non-thermal process is dominant and photons are expected to be polarized in many objects. • Low background (~10 mCrab) and large effective area (240 cm2): very high sensitivity for polarization. plastic scintillator passive/active collimator side BGO bottom BGO PMT

  7. Uniqueness of PoGO Extremely high sensitivity • Ultra-low BG: only 10-20 mCrab • Large Effective Area: 230 cm2 @40 keV • Narrow FOV: 1.25 msr minimum detectable pol. degree is ~3 % for 100 mCrab (1s) by a single, 6 hours balloon flight Modulation Curve for 100 mCrab source Expected source and BG spectra 1 Crab 100 mCrab Signal/BG=5 MF=23.79+-0.72 % BG BG total (CXB/ atmospheric downward/upward) • Balloon-borne mission: • very low cost • possible observation of flaring events (alerted by, e.g., GLAST)

  8. Collaboration/Schedule of the Mission • United States: NASA/GSFC, SLAC and Princeton Univ. • Balloon Flight, DAQ, Beam Test and plastic scintillators • Japan: Tokyo Institute of Technology, Hiroshima Univ., Yamagata Univ. and JAXA/ISAS • PMTs, Beam Test and MC Simulation • Sweden and France: Royal Institute of Technology, Stockholm Univ. and Ecole Polytechnique • PMTs, BGO scintillators and Reflectors 2006 2008 2003 2004 2005 2007 Proposal to NASA Proton Beam Test (Osaka) PoGO Balloon Flight Spring8/Argonne Beam Test KEK Beam Test KEK/Argonne Beam Test 1st prototype (fast scinti. 7 units) 2nd prototype (fast/slow 19 units+anti) Flight Instrument Integration and Test GLAST Launch & Obs.

  9. Argonne Beam Test (2003) • 60,73 and 83 keV synchrotron beam • Tested prototype detector (7 units fast scintillators) as well as Geant4 simulaiton Modulation Curve for 73 keV beam Modulation Factor: 42+-1 %(data) vs. ~47 %(simulation) beam direction • Validated prototype on 10 % level. • Bugs in Geant4 (pol. processes in Rayleigh scattering and Compton Scattering) were found and reported. (more than a year ago….) • Details are in Mizuno et al. (NIMA, 2005).

  10. KEK Beam Test (2004) • 30,50 and 70 keV synchrotron beam • Tested prototype detector with flight-design PMTs Beam Injection • Flight configuration scintillators and PMTs were tested. • Lowest energy X-rays for PoGO were tested and validated. • Details are in Kataoka et al. (SPIE, 2005).

  11. Laboratory Test of prototype (2005) • 2nd prototype with a long hexagonal slow tube and BGO is now being tested. • Used a strong Am source and Compton Scattering technique to generate polarized X-rays in laboratory: very low cost and high flexibility. • M. Ueno (Titech), K. Yamamoto (Hiroshima Univ), T.P. Ylinen and B.G. Kiss (KTH) 3 days data for 0 degree run Pulse Shape Discrimination technique to select fast scint. events. slow shaper out MF = 22+-6 % (taking BG into account) consistent with G4 sim. fast shaper out This new prototype will be tested at KEK next month.

  12. Possible Targets for PoGO(1) Crab Pulsar obs. by PoGO can distinguish among pulsar emission models Modulation Curve for the 1st peak Dyks and Rudak, ApJ, 2003 polar cap model caustic model outer gap model Caustic Polar cap Outer gap GeV gamma-ray spectrum from Vela pulsar Outer gap model Polar cap model GLAST + PoGO will provide a very strong restriction on the pulsar emission mechanism. E2*Flux 0.1 1 10 100 GeV

  13. Possible Target for PoGO (2) Geometry of Astrophysical Jets Multi-band spectrum of Mrk 501 • High Frequency-Peaked BL Lac Objects (HBL) • observe in flaring state notified by, e.g., GLAST. • Multi-wavelength spectrum by GLAST and PoGO can also constrain the jet mechanism. • Galactic microquasars • GRS 1915+105/GRO J1655-40 20 MeV-300 GeV (GLAST) 30-100 keV (PoGO) Other Possible Targets • Galactic BHBs in hard state: accretion disk geometry • Cyg X-1, GX339-4, etc. • Binary pulsars with cyclotron line: propagation of photons in magnetic field • Her X-1, Cen X-3, Vela X-1, etc. ~10 Galactic/extragalactic high energy object could be observed by PoGO

  14. Summary • PoGO is a balloon-borne instrument scheduled to be launched in 2008 and will open an new window in high energy astrophysics, i.e., polarization. • It is based on a well-type phoswich counter design and has a very high sensitivity down to 10 % polarization from 100 mCrab source. ~10 Galactic/extragalactic objects could be observed. • Test of the 2nd prototype started. • Collaboration of GLAST and PoGO will provide a strong constrain on the emission mechanism of pulsars, AGN/micro-quasar jets, etc.

  15. Backup Slides Backup Slides for discussion

  16. Galactic Black Hole Binaries

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