The precise reconstruction of Compton-scatter events is paramount for an imaging medium-energy gamma-ray telescope. The proposed AMEGO-X is enabled by a silicon tracker utilizing AstroPix chips - a pixelated silicon HVCMOS sensor novel for space use. To achieve science goals, each 500 × 500 μm2 pixel must be sensitive for energy deposits ranging from 25 - 700 keV with an energy resolution of 5 keV at 122 keV (< 10%). This is achieved through depletion of the 500 μm thick sensor, although complete depletion poses an engineering and design challenge. This talk will summarize the current status of depletion measurements highlighting direct measurement with TCT laser scanning and the agreement with simulation. Future plans for further testing will also be identified.
A next-generation medium-energy (100 keV to 100 MeV) gamma-ray observatory will greatly enhance the identification and characterization of multimessenger sources in the coming decade. Coupling gamma-ray spectroscopy, imaging, and polarization to neutrino and gravitational wave detections will develop our understanding of various astrophysical phenomena including compact object mergers, supernovae remnants, active galactic nuclei and gamma-ray bursts. An observatory operating in the MeV energy regime requires technologies that are capable of measuring Compton scattered photons and photons interacting via pair production. AstroPix is a monolithic high voltage CMOS active pixel sensor which enables future gamma-ray telescopes in this energy range. AstroPix’s design is iterating towards low-power (∼1.5mW/cm2), high spatial (500 μm pixel pitch) and spectral (<5 keV at 122 keV) tracking of photon and charged particle interactions. Stacking planar arrays of AstroPix sensors in three dimensions creates an instrument capable of reconstructing the trajectories and energies of incident gamma rays over large fields of view. A prototype multi-layered AstroPix instrument, called the AstroPix Sounding rocket Technology demonstration Payload (A-STEP), will test three layers of AstroPix “quad chips” in a suborbital rocket flight. These quad chips (2×2 joined AstroPix sensors) form the 4×4 cm2 building block of future large area AstroPix instruments, such as ComPair-2 and AMEGO-X. This payload will be the first demonstration of AstroPix detectors operated in a space environment and will demonstrate the technology’s readiness for future astrophysical and nuclear physics applications. In this work, we overview the design and state of development of the A-STEP payload.
Many questions posed in the Astro2020 Decadal survey in both the New Messengers and New Physics and the Cosmic Ecosystems science themes require a gamma-ray mission with capabilities exceeding those of existing (e.g. Fermi, Swift) and planned (e.g. COSI) observatories. ComPair, the Compton Pair telescope, is a prototype of such a next-generation gamma-ray mission. It had its inaugural balloon flight from Ft. Sumner, New Mexico in August 2023. To continue the goals of the ComPair project to develop technologies that will enable a future gamma-ray mission, the next generation of ComPair (ComPair-2) will be upgraded to increase the sensitivity and low-energy transient capabilities of the instrument. These advancements are enabled by AstroPix, a silicon monolithic active pixel sensor, in the tracker and custom dual-gain silicon photomultipliers and front-end electronics in the calorimeter. This effort builds on design work for the All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) concept that was submitted the 2021 MIDEX Announcement of Opportunity. Here we describe the ComPair-2 prototype design and integration and testing plans to advance the readiness level of these novel technologies.
The ComPair balloon instrument is a prototype of the All-sky Medium Energy Gamma-ray Observatory (AMEGO) mission concept. AMEGO aims to bridge the spectral gap in sensitivity that currently exists from ∼100 keV to ∼100 MeV by being sensitive to both Compton and pair-production events. This is made possible through the use of four subsystems working together to reconstruct events: a double-sided silicon strip detector (DSSD) Tracker, a virtual Frisch grid cadmium zinc telluride (CZT) Low Energy Calorimeter, a ceasium iodide (CsI) High Energy Calorimeter, and an anti-coincidence detector (ACD) to reject charged particle backgrounds. Composed of 10 layers of DSSDs, ComPair’s Tracker is designed to measure the position of photons that Compton scatter in the silicon, as well as reconstruct the tracks of electrons and positrons from pair-production as they propagate through the detector. By using these positions, as well as the absorbed energies in the Tracker and 2 Calorimeters, the energy and direction of the incident photon can be determined. This proceeding will present the development, testing, and calibration of the ComPair DSSD Tracker and early results from its balloon flight in August 2023.
The ComPair balloon instrument is a prototype gamma-ray telescope that aims to further develop technology for observing the gamma-ray sky in the MeV regime. ComPair combines four detector subsystems to enable parallel Compton scattering and pair-production detection, critical for observing in this energy range. This includes a 10 layer double-sided silicon strip detector tracker, a virtual Frisch grid low energy CZT calorimeter, a high energy CsI calorimeter, and a plastic scintillator anti-coincidence detector. The inaugural balloon flight successfully launched from the Columbia Scientific Balloon Facility site in Fort Sumner, New Mexico, in late August 2023, lasting approximately 6.5 hours in duration. In this proceeding, we discuss the development of the ComPair balloon payload, the performance during flight, and early results.
The ComPair gamma-ray telescope is a technology demonstrator for a future gamma-ray telescope called the All-sky Medium Energy Gamma-ray Observatory (AMEGO). The instrument is composed of four subsystems, a double-sided silicon strip detector, a virtual Frisch grid CdZnTe calorimeter, a CsI:Tl based calorimeter, and an anti-coincidence detector (ACD). The CsI calorimeter's goal is to measure the position and energy deposited from high-energy events. To demonstrate the technological readiness, the calorimeter has flown onboard a NASA scientific balloon as part of the GRAPE-ComPair mission and accumulated around 3 hours of float time at an altitude of 40 km. During the flight, the CsI calorimeter observed background radiation, Regener-Pfotzer Maximum, and several gamma-ray activation lines originating from aluminum.
All-sky medium-energy gamma-ray observations are essential to deepen our understanding of physics in high energy astronomical phenomena, and to further develop multi-messenger astronomy. Future all-sky MeV gamma-ray telescopes must have a large area detector and keep high sensitivities even in the energies in which Compton scattering is dominant. AMEGO-X is one of the proposed MeV gamma-ray missions and its gamma-ray detector consists of silicon trackers and calorimeters. In order to efficiently detect MeV photons and to have precise Compton reconstruction, the silicon sensors must be fully depleted (500 μm) and have a moderate position resolution (∼ 500 μm) with a good energy resolution (< 10% at 60 keV). On top of that, the power consumption of the silicon detector must be low (< 1.5 mW/cm2) given the required silicon area in the gamma-ray detector is huge (∼ 24 m2). We have been developing AstroPix, a high-voltage CMOS active pixel sensor, to fulfill such specifications. In this contribution, we report basic characterization of the third version of AstroPix chip (AstroPix3), such as I-V measurement, imaging capability, energy spectrum, and indirect depletion depth measurements using gamma-ray sources.
KEYWORDS: Space operations, Sensors, Equipment, Gamma radiation, Signal detection, Silicon photomultipliers, Data archive systems, Observatories, Data processing, Design
BurstCube is a 6U (10 x 20 x 30 cm) CubeSat designed to detect gamma-ray bursts (GRBs) and enable multimessenger observations, scheduled to launch in early 2024. BurstCube science is informed by the coincident detection of GRB 170817A and gravitational wave (GW) 170817, which confirmed compact binary mergers as progenitors for GRBs. Future coincident detections will also provide important context to the GW measurements - namely constraining the neutron star equation of state and testing fundamental physics, while also probing the origin of GRB prompt emission. Full sky coverage in the gamma-ray regime is needed to increase the likelihood of such measurements. Once in orbit, BurstCube will expand sky coverage while rapidly providing public alerts and localization information to the community using the Tracking and Data Relay Satellite (TDRS) and General Coordinates Network (GCN). This work will describe the current status of the mission, as well as an outline of post-launch operations, performance, and science goals.
ComPair is a prototype gamma-ray telescope for the development of key technologies for next-generation gammaray detectors consisting of four subsystems: a 10-layer double-sided silicon strip detector tracker, a cadmium zinc telluride calorimeter, a cesium iodide calorimeter, and a plastic anti-coincidence detector (ACD). The ACD acts as an active shield to veto charged particle events and consists of 5 plastic scintillating panels. ComPair was launched as a balloon payload from Ft. Sumner, New Mexico and completed a 6-hour flight on August 27, 2023. Here we detail the design and calibration of the ComPair ACD, and report on the ACD’s veto efficiency and other performance metrics during the ComPair flight.
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions and accelerators. The main science themes include supermassive black holes and their connections to neutrinos and cosmic rays; binary neutron star mergers and the relativistic jets they produce; cosmic ray particle acceleration sources including galactic supernovae; continuous monitoring of other astrophysical events and sources over the full sky in this important energy range. AMEGO-X will probe the medium energy gamma-ray band using a single instrument with sensitivity up to an order of magnitude greater than previous telescopes in the energy range 100 keV to 1 GeV that can be only realized in space. During its 3-year baseline mission, AMEGO-X will observe nearly the entire sky every two orbits, building up a sensitive all-sky map of gamma-ray sources and emissions. AMEGO-X was submitted in the recent 2021 NASA MIDEX announcement of opportunity.
There is a growing interest in the science uniquely enabled by observations in the MeV range, particularly in light of multi-messenger astrophysics. The Compton Pair (ComPair) telescope, a prototype of the AMEGO Probe-class concept, consists of four subsystems that together detect and characterize gamma rays in the MeV regime. A double-sided strip silicon Tracker gives a precise measure of the first Compton scatter interaction and tracks pair-conversion products. A novel cadmium zinc telluride (CZT) detector with excellent position and energy resolution beneath the Tracker detects the Compton-scattered photons. A thick cesium iodide (CsI) calorimeter contains the high-energy Compton and pair events. The instrument is surrounded by a plastic anti-coincidence (ACD) detector to veto the cosmic-ray background. In this work, we will give an overview of the science motivation and a description of the prototype development and performance.
Space-based γ-ray telescopes such as the Fermi Large Area Telescope have used single sided silicon strip detectors to track secondary charged particles produced by primary γ-rays with high resolution. At the lower energies targeted by keV-MeV telescopes, two dimensional position information within a single detector is required for event reconstruction—especially in the Compton regime. This work describes the development of monolithic CMOS active pixel silicon sensors—AstroPix—as a novel technology for use in future γ-ray telescopes. Based upon sensors (ATLASPix) designed for use in the ATLAS detector at the Large Hadron Collider, AstroPix has the potential to maintain high performance while reducing noise with low power consumption. This is achieved with the dual detection and readout capabilities in each CMOS pixel. The status of AstroPix development and testing, as well as outlook for future testing and application, will be presented.
This conference presentation was prepared for the conference on Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, part of SPIE Astronomical Telescopes + Instrumentation, 2022.
This paper details preliminary photon measurements with the monolithic silicon detector ATLASPix, a pixel detector built and optimized for the CERN experiment ATLAS. The goal of this paper is to determine the promise of pixelated silicon in future space-based gamma-ray experiments. With this goal in mind, radioactive photon sources were used to determine the energy resolution and detector response of ATLASPix; these are novel measurements for ATLASPix, a detector built for a ground-based particle accelerator. As part of this project a new iteration of monolithic Si pixels, named AstroPix, have been created based on ATLASPix, and the eventual goal is to further optimize AstroPix for gamma-ray detection by constructing a prototype Compton telescope. The energy resolution of both the digital and analog output of ATLASPix is the focus of this paper, as it is a critical metric for Compton telescopes. It was found that with the analog output of the detector, the energy resolution of a single pixel was 7.69 ± 0.13% at 5.89 keV and 7.27 ± 1.18% at 30.1 keV, which exceeds the conservative baseline requirements of 10% resolution at 60 keV and is an encouraging start to an optimistic goal of <2% resolution at 60 keV. The digital output of the entire detector consistently yielded energy resolutions that exceeded 100% for different sources. The analog output of the monolithic silicon pixels indicates that this is a promising technology for future gamma-ray missions, while the analysis of the digital output points to the need for a redesign of future photon-sensitive monolithic silicon pixel detectors.
BurstCube aims to expand sky coverage in order to detect, localize, and rapidly disseminate information about gamma-ray bursts (GRBs). BurstCube is a ’6U’ CubeSat with an instrument comprised of 4 Cesium Iodide (CsI) scintillators coupled to arrays of Silicon photo-multipliers (SiPMs) and will be sensitive to gamma-rays between 50 keV and 1 MeV. BurstCube will assist current observatories, such as Swift and Fermi, in the detection of GRBs as well as provide astronomical context to gravitational wave (GW) events detected by LIGO, Virgo, and KAGRA. BurstCube is currently in its development phase with a launch readiness date in early 2022.
AMEGO is a combined Compton and pair-production telescope designed to survey the sky from ∼ 200 keV to > 10 GeV. The prototype, known as ComPair, will undergo beam tests in 2021 and a short-duration balloon flight the following year. The ComPair tracker is based on ten layers of 10 cm × 10 cm double-sided silicon detectors read out with a custom front-end based on the IDEAS VATA460 ASIC and a Zynq SoC ARM+FPGA running petalinux. In this contribution, we will discuss detector and ASIC characterization, calibration systems, and the overall design of the ComPair silicon tracker.
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