Speaker
Description
The Large Area Telescope onboard the Fermi Gamma-ray Space Telescope (Fermi-LAT) has surveyed the sub-GeV/GeV gamma-ray sky and achieved high statistics measurements since 2008. However, observation at low galactic latitudes remains difficult owing to the lack of the angular resolution, and new issues following the operation of Fermi-LAT have arisen.
We devised a precise gamma-ray observation project, Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE), using balloon-borne emulsion gamma-ray telescopes to realize high angular resolution, polarization-sensitive, and large-aperture observations in the 0.01–100 GeV energy region. The main detector of the telescope, the nuclear emulsion, is a device that can track charged particles with sub-micron accuracy, and by measuring the angle of electron pair tracks and the emission azimuthal angle directly below the gamma-ray conversion point, it has a high angular resolution of 0.1 degrees in the 1 GeV band and the ability to measure polarization in the sub-GeV band. By combining the nuclear emulsion with a time stamper and launching it on a balloon, it is possible to achieve precision observations that would not be possible with satellite projects.
GRAINE's initial targets are high-angular-resolution observations of the Fermi Galactic Center GeV Excess and the first polarization measurement of the Vela pulsar in the sub-GeV band by repeatedly launching balloons from Australia. In the 3rd balloon experiment conducted in 2018, imaging observations of the Vela pulsar in the 100 MeV band were achieved with the world's highest resolution using a small-size emulsion telescope.
This talk comprehensively reports the latest observational results from the Vela pulsar and the Galactic center region from the 4th balloon experiment (conducted in April 2023) that launched a telescope with a 2.5-m$^2$ aperture area 6 times larger than the previous experiment, as well as the technical developments for high-angular resolution and polarization measurements using an emulsion telescope, and the preparation status towards further scientific observations using larger telescopes and long-duration balloon flights.
| Collaboration(s) | GRAINE |
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