Observation of diffuse cosmic and atmospheric gamma rays at balloon altitudes with an electron-tracking compton camera

Atsushi Takada, Hidetoshi Kubo, Hironobu Nishimura, Kazuki Ueno, Kaori Hattori, Shigeto Kabuki, Shunsuke Kurosawa, Kentaro Miuchi, Eiichi Mizuta, Tsutomu Nagayoshi, Naoki Nonaka, Yoko Okada, Reiko Orito, Hiroyuki Sekiya, Atsushi Takeda, Toru Tanimori

Research output: Contribution to journalArticlepeer-review

41 Citations (Scopus)

Abstract

We observed diffuse cosmic and atmospheric gamma rays at balloon altitudes with the Sub-MeV gamma-ray Imaging Loaded-on-balloon Experiment I (SMILE-I) as the first step toward a future all-sky survey with a high sensitivity. SMILE-I employed an electron-tracking Compton camera comprised of a gaseous electron tracker as a Compton-scattering target and a scintillation camera as an absorber. The balloon carrying the SMILE-I detector was launched from the Sanriku Balloon Center of the Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency on 2006 September 1, and the flight lasted for 6.8hr, including level flight for 4.1hr at an altitude of 32-35km. During the level flight, we successfully detected 420 downward gamma rays between 100keV and 1MeV at zenith angles below 60°. To obtain the flux of diffuse cosmic gamma rays, we first simulated their scattering in the atmosphere using Geant4, and for gamma rays detected at an atmospheric depth of 7.0gcm-2 we found that 50% and 21% of the gamma rays at energies of 150keV and 1MeV, respectively, were scattered in the atmosphere prior to reaching the detector. Moreover, by using Geant4 simulations and the QinetiQ atmospheric radiation model, we estimated that the detected events consisted of diffuse cosmic and atmospheric gamma rays (79%), secondary photons produced in the instrument through the interaction between cosmic rays and materials surrounding the detector (19%), and other particles (2%). The obtained growth curve was comparable to Ling's model, and the fluxes of diffuse cosmic and atmospheric gamma rays were consistent with the results of previous experiments. The expected detection sensitivity of a future SMILE experiment measuring gamma rays between 150keV and 20MeV was estimated from our SMILE-I results and was found to be 10 times better than that of other experiments at around 1MeV.

Original languageEnglish
Article number13
JournalAstrophysical Journal
Volume733
Issue number1
DOIs
Publication statusPublished - 2011 May 20
Externally publishedYes

Keywords

  • balloons
  • diffuse radiation
  • gamma rays: diffuse background
  • instrumentation: detectors

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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