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Title: Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN Jets: Design and Calibration(SULI)

Abstract

Polarization measurements at X-ray and gamma-ray energies can provide crucial information on the emission region around massive compact objects such as black holes and neutron stars. The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrument designed to measure polarization from such astrophysical objects in the 30-100 keV range, under development by an international collaboration with members from United States, Japan, Sweden and France. The PoGO instrument has been designed by the collaboration and several versions of prototype models have been built at SLAC. The purpose of this experiment is to test the latest prototype model with a radioactive gamma-ray source. For this, we have to polarize gamma-rays in a laboratory environment. Unpolarized gamma-rays from Am241 (59.5 keV) were Compton scattered at around 90 degrees for this purpose. Computer simulation of the scattering process in the setup predicts a 86% polarization. The polarized beam was then used to irradiate the prototype PoGO detector. The data taken in this experiment showed a clear polarization signal, with a measured azimuthal modulation factor of 0.35 {+-} 0.02. The measured modulation is in very close agreement with the value expected from a previous beam test study of a polarized gamma-ray beam at the Argonnemore » National Laboratories Advanced Photon Source. This experiment has demonstrated that the PoGO instrument (or any other polarimeter in the energy range) can be tested in a libratory with a simple setup to a similar accuracy.« less

Authors:
;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
877479
Report Number(s):
SLAC-TN-05-058
TRN: US0601501
DOE Contract Number:
AC02-76SF00515
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ACCURACY; ADVANCED PHOTON SOURCE; BLACK HOLES; COMPUTERIZED SIMULATION; ENERGY RANGE; KEV RANGE; MODULATION; NEUTRON STARS; POLARIMETERS; POLARIZATION; POLARIZED BEAMS; PULSARS; SCATTERING; STANFORD LINEAR ACCELERATOR CENTER; Astrophysics,ASTROPHYS

Citation Formats

Apte, Zachary, and /Hampshire Coll. /SLAC. Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN Jets: Design and Calibration(SULI). United States: N. p., 2005. Web. doi:10.2172/877479.
Apte, Zachary, & /Hampshire Coll. /SLAC. Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN Jets: Design and Calibration(SULI). United States. doi:10.2172/877479.
Apte, Zachary, and /Hampshire Coll. /SLAC. Thu . "Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN Jets: Design and Calibration(SULI)". United States. doi:10.2172/877479. https://www.osti.gov/servlets/purl/877479.
@article{osti_877479,
title = {Balloon-Borne Gamma-Ray Polarimeter (PoGO) to Study Black Holes, Pulsars, and AGN Jets: Design and Calibration(SULI)},
author = {Apte, Zachary and /Hampshire Coll. /SLAC},
abstractNote = {Polarization measurements at X-ray and gamma-ray energies can provide crucial information on the emission region around massive compact objects such as black holes and neutron stars. The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrument designed to measure polarization from such astrophysical objects in the 30-100 keV range, under development by an international collaboration with members from United States, Japan, Sweden and France. The PoGO instrument has been designed by the collaboration and several versions of prototype models have been built at SLAC. The purpose of this experiment is to test the latest prototype model with a radioactive gamma-ray source. For this, we have to polarize gamma-rays in a laboratory environment. Unpolarized gamma-rays from Am241 (59.5 keV) were Compton scattered at around 90 degrees for this purpose. Computer simulation of the scattering process in the setup predicts a 86% polarization. The polarized beam was then used to irradiate the prototype PoGO detector. The data taken in this experiment showed a clear polarization signal, with a measured azimuthal modulation factor of 0.35 {+-} 0.02. The measured modulation is in very close agreement with the value expected from a previous beam test study of a polarized gamma-ray beam at the Argonne National Laboratories Advanced Photon Source. This experiment has demonstrated that the PoGO instrument (or any other polarimeter in the energy range) can be tested in a libratory with a simple setup to a similar accuracy.},
doi = {10.2172/877479},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 15 00:00:00 EST 2005},
month = {Thu Dec 15 00:00:00 EST 2005}
}

Technical Report:

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  • We are developing a new balloon-borne instrument (PoGO), to measure polarization of soft gamma rays (25-200 keV) using asymmetry in azimuth angle distribution of Compton scattering. PoGO will 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 technology used in balloon-borne experiments (Welcome-1) and AstroE2 Hard X-ray Detector. PoGO consists of close-packed array of 397 hexagonal well-type phoswich counters. Each unit is composed ofmore » a long thin tube (well) of slow plastic scintillator, a solid rod of fast plastic scintillator, and a short BGO at the base. A photomultiplier coupled to the end of the BGO detects light from all 3 scintillators. The rods with decay times < 10 ns, are used as the active elements; while the wells and BGOs, with decay times {approx}250 ns are used as active anti-coincidence. The fast and slow signals are separated out electronically. When gamma rays entering the field-of-view (fwhm {approx} 3deg{sup 2}) strike a fast scintillator, some are Compton scattered. A fraction of the scattered photons are absorbed in another rod (or undergo a second scatter). A valid event requires one clean fast signal of pulse-height compatible with photo-absorption (> 20keV) and one or more compatible with Compton scattering (< 10keV). Studies based on EGS4 (with polarization features) and Geant4 predict excellent background rejection and high sensitivity.« less
  • Polarization measurements in the X-ray and gamma-ray energy range can provide crucial information on massive compact objects such as black holes and neutron stars. The Polarized Gamma-ray Observer (PoGO) is a new balloon-borne instrument designed to measure polarization from astrophysical objects in the 30-100 keV range, under development by an international collaboration with members from United States, Japan, Sweden and France. To examine PoGO's capability, a beam test of a simplified prototype detector array was conducted at the Argonne National Laboratory Advanced Photon Source. The detector array consisted of seven plastic scintillators, and was irradiated by polarized photon beams atmore » 60, 73, and 83 keV. The data showed a clear polarization signal, with a measured modulation factor of 0.42 {+-} 0.01. This was successfully reproduced at the 10% level by the computer simulation package Geant4 after modifications to its implementation of polarized Compton/Rayleigh scattering. Details of the beam test and the validation of the Geant4 simulations are presented.« less
  • 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 consistsmore » 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.« less
  • Instrumental background in balloon-borne gamma-ray spectrometers is presented. The calculations are based on newly available interaction cross sections and new analytic techniques, and are the most detailed and accurate published to date. Results compare well with measurements made in the 20 keV to 10 MeV energy range by the Goddard Low Energy Gamma-ray Spectrometer (LEGS). The principal components of the continuum background in spectrometers with GE detectors and thick active shields are: (1) elastic neutron scattering of atmospheric neutrons on the Ge nuclei; (2) aperture flux of atmospheric and cosmic gamma rays; (3) beta decays of unstable nuclides produced bymore » nuclear interactions of atmospheric protons and neutrons with Ge nuclei; and (4) shield leakage of atmospheric gamma rays. The improved understanding of these components leads to several recommended techniques for reducing the background.« less
  • A high resolution gamma ray spectrometer for stellar measurements was developed. The instrument consists of a large Ge(Li) crystal (140 cu cm) cooled at liquid nitrogen temperature and actively shielded by a sodium iodide crystal. Spectral resolution and effective area are respectively 3.0 KeV (F.W.H.M.) and 2.7 sq cm at 1 MeV. Three successful flights were carried on board a stabilized gondola. The background total counting rate was about 10 counts/s in the 0.1-8 MeV energy range at floating altitude (2.8g/sq cm residual atmosphere, 12 GV cut off-rigidity). The sensitivity of the detector is about 10 to the minus threemore » power/sq cm/s over the energy range for three hours of observation of a point source. Preliminary results and future developments are described.« less