J. Mitchell

A. Harding

S. Hunter

T. Takahashi

Taiji Mizuno

E. Groth

P. Chen

L. Barbier

G. Bogaert

H. Tajima

Y. Fukazawa

J. Ng

J. Krizmanic

R. Streitmatter

R. Fernholz

P. Bloser

T. Kamae

V. Andersson

G. Madejski

Y. Saito

Goddard /Princeton U. /Royal Ins NASA

We are developing a new balloon-borne instrument (PoGO), to measure polarization of soft gamma rays (30-200 keV) using asymmetry in azimuth angle distribution of Compton scattering. PoGO is designed to detect 10% polarization in 100mCrab sources in a 6-8 hour observation and bring a new dimension to studies on gamma ray emission/transportation mechanism in pulsars, AGNs, black hole binaries, and neutron star surface. The concept is an adaptation to polarization measurements of well-type phoswich counter consisting of a fast plastic scintillator (the detection part), a slow plastic scintillator (the active collimator) and a BGO scintillator (the bottom anti-counter). PoGO consists of close-packed array of 217 hexagonal well-type phoswich counters and has a narrow field-of-view ({approx} 5 deg{sup 2}) to reduce possible source confusion. A prototype instrument has been tested in the polarized soft gamma-ray beams at Advanced Photon Source (ANL) and at Photon Factory (KEK). On the results, the polarization dependence of EGS4 has been validated and that of Geant4 has been corrected.

Large-Area Balloon-Borne Polarized Gamma Ray Observer (PoGO).

Goddard /Princeton U. /Royal Ins NASA

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