High Energy Polarimetry Missons in Japan; PoGOLite, SPHiNX, PolariS Hiromitsu Takahashi (Hiroshima University) hirotaka@hep01.hepl.hiroshima-u.ac.jp PoGOLite balloon 10m (2013~) SPHiNX satellite 0.5m (Plan: 2016~) PolariS satellite 6m (Plan: 2020~)
Crab Polarized Sources Synchrotron emission: - Rotation-powered neutron stars (e.g. Crab pulsar) - Pulsar wind nebulae (e.g. Crab nebula) - Jets in active galactic nuclei (e.g. Mkn 501, 1E1959+65) - Gamma-ray bursts Compton scattering: - Accretion disk around black holes (e.g. Cygnus X-1) Propagation in strong magnetic field: - Highly magnetized neutron stars (e.g. Hercules X-1, Magnetars) Cygnus X-1 Scattering Synchrotron emission
Polarization Measurement (X/gamma-ray) - Polarization measurements in X/gamma-rays have been expected to provide a powerful probe into high-energy emission mechanism around pulsars, black hole binaries, active galactic nuclei etc. - However, X/gamma-ray polarization has been measured only GRBs and at 2.6/5.2 kev and above 200 kev from the Crab nebula and Cyg X-1. - Additional measurements (middle10s kev band / other sources) are needed (New missions: TSUBAME, ASTRO-H, SPHiNX, GEMS, Polaris ). (c) astro.psu.edu Gamma-ray (25-80 kev) ~40 km
Polarimeter Design Figure of Merit: Minimum Detectable Polarisation (3σ) Bragg-reflected photons, Photo-electrons Compton-scattered photons Pair-created e+/etend to be detected one direction. Background rate Good mirror, Shielding Modulation for 100% polarized source Good position resolution Signal rate Good mirror, Large effective area Observation time
Polarimeter Design Modulation curve Figure of Merit: Minimum Detectable Polarisation (3σ) Bragg-reflected photons, Photo-electrons Compton-scattered photons Pair-created e+/etend to be detected one direction. Background rate Good mirror, Shielding Modulation factor Modulation for 100% polarized source Good position resolution Signal rate Good mirror, Large effective area Observation time Polarization degree
Future Satellite Missions (by Tamagawa) PoGOLite balloon (2010~) Source : faint Mirror/background rejection : needed => US: SMEX, JP: Small satellite AOs GAP (2010~) GRB : bright Very small satellite: OK Green: will be launched Red: Plan 日 :Japan, ス :Sweden 米 :US
Polarized Gamma-ray Observer (PoGOLite) Hiromitsu Takahashi (Hiroshima University) hirotaka@hep01.hepl.hiroshima-u.ac.jp Sweden (KTH, Stockholm Univ., Esrange, DST Control) Japan (Hiroshima Univ., Nagoya Univ., Waseda Univ., Tokyo Tech., ISAS/JAXA) US (SLAC, Univ. of Hawaii) PI: Mark Pearce (KTH, Royal Institute of Technology) www.particle.kth.se/pogolite
Polarized Gamma-ray Observer (PoGOLite) - The Polarized Gamma-ray Observer, PoGOLite, is a balloon experiment with the capability of detecting 10% polarization from a 200 mcrab celestial object in the energy-range 25 80 kev. (1 Crab ~ 0.2 photons/s/cm2 @30 kev, power-law index ~ 2.1) - The project is international collaboration including Japan, Sweden and US. - Its pathfinder flight took place in the summer of 2013 from Kiruna, Sweden (c) astro.psu.edu Gamma-ray (25-80 kev) ~40 km Weight (wo ballast) : ~1750 kg Power : ~300 W (Instrument) ~200 W (Gondola, etc.)
Pathfinder Flight from Sweden Flight Plan (1-day long) Crab nebula (Pulsar) Cyg X-1 (Black hole binary) (c) ESA Solar flare (c) JAXA (c) astro.psu.edu PoGOLite: - large effective area, low background => Suitable for bright sources. - long exposure => high statistics, variability, flaring activities.
Flight Record of PoGOLite - In the summer 2010, there was a plan of 1 or 2-day flight @ Kiruna However, it was cancelled due to NASA launch failure in Australia in April 2010 - At 23:57, July 6th, 2011 (UTC), there was a successful launch @ Kiruna The flight was planned toward Canada (duration ~5 days). However, there was He-leak from the balloon, and the gondola was returned to ground after ~5 hours. - July, 2012, the gondola became flight ready @ Kiruna for 2-week circumpolar flight. However, weather was bad, flight was cancelled. - July 14~26, 2013, there was a successful flight from Kiruna, Sweden to Norilsk, Russia.
Detector Concept (1) : Detection - PoGOLite captures a pair of Compton scattering and photoabsorption for one X/gamma-ray event with 217 well-type phoswich detector cells (PDCs), and measure the azimuthal angle anisotropy of Compton-scattering. - In the pathfindr flight, there are 61 PDCs. - Instrument is rotated (5~15 mins/rotation) to cancel instrumental systematics. Gamma-ray Top view PDCs SAS 1 m Slow plastic scintillator Fast plastic scintillator Bottom BGO PMTs PDCs in one direction detect more events than ones in other directions.
Detector Concept (2) : Low background Count rate of background from charged particles, neutrons and X/gammaray from other sources is ~1000 times higher than that of the signal. Shields of BGO scintillator (SAS) and polyethylene locate around PDCs. Each PDC is a well-type phoswich detector has narrow FOV (~ 1 deg). Charged particles and X/gamma-rays are rejected ~100% The remaining background is neutron-scatter events. Gamma-ray 1 deg PDC unit PDCs SAS 1 m Slow plastic scintillator Fast plastic scintillator Bottom BGO PMTs
Principle Modulation curve Slow plastic scintillator collimator Valid event Off-axis event (vetoed by hit in slow scintillator) BGO anticoincidence Side-entering event (vetoed by hit side anticoincidence BGO shield) Fast plastic scintillator scatterer Modulation factor Polyethylene neutron shield Back-entering event (vetoed by hit in BGO) Neutron event (background) Polarization degree
Polarimeter Design Figure of Merit: Minimum Detectable Polarisation (3σ) Background rate Small field-of-view: low aperture background. BGO anticoincidence: low γ + particle backgrounds Polyethylene shielding: suppresses dominant neutron background μ Modulation for 100% polarized source Signal rate Area, geometry, efficiency. Hexagonal crosssection plastic scintillators: ~40 cm 2 (full-size: ~200 cm 2 ) @ 50 kev for a reasonable MF (~30% @ 50 kev). Observation time Long duration balloon flight
Detector Installation All the 91 units are installed successfully.
Polarimeter and Star Trackers STM star tracker (2.57 x 1.92 deg) STR star tracker (5.0 x 3.7 deg) Aurora monitor unit
PoGOLite Overall View (2013)
PoGOLite Overall View (2011)
Launch (2013/7/12)@Kiruna 19
Launch (2013/7/12)@Kiruna 20
Operation 21
Trajectory (14 days) Kiruna Latitude 68 Altitude 39~40 km (day), ~36 km (night) 22
Trajectory (14 days) Launch 2013-07-12 08:18 UT Cut 2013-07-25 23:24 UT Landing 2013-07-26 00:15 UT! 23
Attitude Control (for 7 hours) (Deg) RA DEC - Attitude Control System worked for 14 days Requirement (~0.1 deg accuracy) is archived (GOOD) - Polarimeter worked for first 3 days After that, there was a power trouble. (Time) 24
Landing (2013/7/26)@Russia Gondola has been delivered from Russia to Sweden in Jan. (Export is difficult ) 25
SPHiNX satellite 0.5m (Plan: 2016~) PolariS satellite 6m (Plan: 2020~) Launched by Swedish satellite - GRB dedicated (50-500 kev) 25 detections / year - Large effective area: 120 cm 2 - Effective area is ~10 times larger than GAP/TSUBAME. - Modulation factor is similar to GAP (TSUBAME has twice better modulation factor). Launched by Japanese Epsilon rocket - 2-80 kev hard X-ray band >10 mcrab sources. - Hard X-ray mirror (like ASTRO-H) gain effective area reduce backgrounds
PolariS targets (by Hayashida)
Summary (by Tamagawa) PoGOLite balloon (2010~) Source : faint Mirror/background rejection : needed => US: SMEX, JP: Small satellite AOs GAP (2010~) GRB : bright Very small satellite: OK It is Green: high-time will be for launched dedicated instruments for polarized X-ray astrophysics. Several Red: Plan groups are pursuing balloon- and satellite-borne instruments.