KICP Colloquium: James Buckley (Washington University in St. Louis)

3:30–4:30 pm ERC 161

James Buckley (Washington University in St. Louis) "The Advanced Particle-astrophysics Telescope (APT)"

I will present the case for a next-generation space-based gamma-ray observatory aimed at resolving a number or key questions in particle astrophysics ranging from the nature of dark matter to the origin of the heavy chemical elements. The instrument will also add a key multimessenger capability, providing prompt sub-degree localization of electromagnetic counterparts for gravitational wave sources and other astrophysical transients. I’ll make the case that such an instrument is capable of either detecting or ruling out the entire natural parameter space for thermal WIMPs, not only by resolving the GeV excess at the Galactic center but by providing robust constraints on stacked dwarf galaxies. The concept, called the Advanced Particle-astrophysics Telescope (APT), is based on a new detector design that will allow us to substantially increase the effective area compared to Fermi, add Compton imaging for MeV observations, and add key capabilities for cosmic-ray measurements - becoming a true astroparticle physics observatory. By using scintillating fibers and a distributed imaging CsI calorimeter, it is possible to realize an order of magnitude in effective area compared to Fermi in the 20 MeV to TeV energy range at about the same mission cost (somewhere between a MIDEX and Probe class mission). Putting the instrument in a Lagrange orbit would double the GeV field of view compared to Fermi, and provide an almost 4-pi steradian instantaneous MeV field of view with sub-degree localization. But developing and demonstrating this low-cost technical approach is key to enabling this mission concept. As a first major step toward this goal, the APT team is constructing the Antarctic Demonstrator for APT (ADAPT), a ballon-born instrument scheduled for an Antarctic flight in 2025. ADAPT will have an active detector area of 0.45m x 0.45m and will consist of 4 imaging CsI calorimeter (ICC) models, 4 layers of scintillating fiber trackers, and 4 integrating CsI (tail) counters. The ICC and tracker modules provide Compton imaging (in the MeV regime) and pair reconstruction (up to several GeV). With no passive converter layers, the pair telescope will reach lower energies (and larger effective areas) than Fermi in the tens of MeV to 100 MeV regime, providing the best instantaneous sensitivity for flaring sources. In addition, a silicon strip detector (SSD) covering the top layer of the instrument will provide cosmic-ray charge measurements, while also serving as a technical demonstration of SSDs for Compton imaging. To achieve a design that can be scaled to a much larger area (2.5m x 2.5m) and still fit in the cost envelope for a future midsize or probe-scale mission, APT (and ADAPT) make use of scintillating fibers both for the tracker and ICC readout by Silicon Photomultipliers (SiPMs) custom low-power preamplifier and custom analog pipeline waveform digitizer ASICs (the SMART and ALPHA ASICs). ADAPT will serve as a technology demonstrator for these detector components, as well as on-board firmware (e.g., VHDL running on FPGAs) and software for real-time data reduction and event reconstruction, including a complete pipeline for real-time Compton reconstruction and localization of MeV transients. The ADAPT mission should provide prompt (on-board) degree-scale localizations and provide polarization constraints on several GRBs during a 30 day flight.

Event Type


Oct 18