New Mission Concept: Galactic Explorer with Coded Aperture Mask Compton Telescope (GECCO)

by Alexander Moiseev (University of Maryland, CRESST/NASA Goddard Space Flight Center)

Thursday 17 Sept 2020, 15:00 → 16:00 US/Eastern

We present a novel concept for a next-generation γ-ray telescope that will cover the hard X-ray - soft γ-ray region. Despite the progress made by the European Space Observatory INTEGRAL, this energy range is still under-explored. GECCO will conduct high-sensitivity measurements of the cosmic γ-radiation in the energy range from 100 keV to ∼10 MeV and create intensity maps with high spectral and spatial resolution, focusing on sensitive separation of diffuse and point- source components. These observations will enable the following major objectives for GECCO: a) understand the nature of the central supermassive black hole environment and sources at the Galactic Center (GC); b) resolve heavily populated sky regions, including tangential directions to the spiral arms in the Galactic plane; c) localize and discern the origin(s) of the 511 keV positron annihilation line; d) decipher the origin(s) of the Fermi Bubbles by mapping the Bubbles and especially their bases near the GC; e) resolve Galactic chemical evolution and sites of explosive element synthesis by conducting high-sensitivity measurements of nuclear lines; f) test as-yet unexplored candidates for the dark matter.

The instrument is based on a novel CdZnTe Imaging calorimeter and a deployable coded aperture mask. It utilizes a heavy-scintillator shield and plastic scintillator anti-coincidence detectors. The unique feature of GECCO is that it combines the advantages of two techniques – the high-angular resolution possible with coded mask imaging, and a Compton telescope mode providing high sensitivity measurements of diffuse radiation. With this combined “Mask+Compton” operation we will separate diffuse and point-sources components in the GC radiation with high sensitivity. GECCO will be operating mainly in the pointing mode, focusing on the Galactic Center and other regions of interest. It can be quickly re-pointed to any other region, when alarmed. Expected GECCO performance is as follows: energy resolution <1% at 0.5-5 MeV, angular resolution ∼1 arcmin in the Mask mode (2-3 degree field-of-view, ∼2,000 cm2 effective area), and 3-5 degrees in the Compton mode (15-20 degree field-of-view, ∼500 cm2 effective area). The sensitivity is expected to be better than 10−6MeV/cm2/s at 1 MeV. GECCO can be considered for a future NASA Explorer mission.

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