Future x-ray observatories will require imaging detectors with fast readout speeds that simultaneously achieve or exceed the other high-performance parameters of x-ray charge-coupled devices used in many missions over the past three decades. Fast readout will reduce the impact of pile-up in missions with large collecting areas while improving the performance in other respects, such as timing resolution. Event-driven readout, in which only pixels with charge from x-ray events are read out, can be used to achieve these faster operating speeds. Speedster-EXD550 detectors are hybrid complementary metal-oxide semiconductor detectors capable of event-driven readout that were developed by Teledyne Imaging Sensors and Penn State University. We present the initial results from measurements of the first of these detectors, demonstrating their capabilities and performance in both full-frame and event-driven readout modes. These include dark current, read noise, gain variation, and energy resolution measurements from the first two engineering-grade devices.
BlackCAT is a NASA CubeSat mission planned to be launch-ready in early 2025. Using a wide-field telescope, this 6U CubeSat will monitor the soft x-ray sky, searching for high-redshift Gamma-Ray Bursts (GRBs), gravitational-wave counterparts, and other transient events. After detecting burst events, BlackCAT will be capable of transmitting rapid alerts to enable prompt follow-up observations. The instrument is composed of a coded-aperture telescope using an array of event-driven x-ray Hybrid CMOS Detectors (HCDs) in its focal plane. In this paper, we provide a brief update on the design and status of the mission.
The novel Speedster-EXD550 is a 550×550-pixel x-ray Hybrid CMOS Detector (HCD) with event-driven readout capabilities and 40-micron pixel pitch. In event-driven readout mode, only the pixels that contain sufficient liberated charge from the absorption of an x-ray will be read out. Event-driven readout allows for even faster readout speed than other HCDs, reaching readout speeds up to 10,000 frames/sec. The high frame rate of the Speedster-EXD550 is desirable for future missions as the effects of dark current and x-ray pile-up will be reduced. The readout circuitry within the ROIC for the Speedster-EXD550 contains a high-gain capacitive transimpedance amplifier, in-pixel correlated double sampling, and an in-pixel comparator enabling event-driven readout. The Speedster-EXD550 also utilizes column-parallel on-chip digitization. The ability of the Speedster-EXD550 will be demonstrated on BlackCAT, a funded NASA CubeSat mission. Testing and characterization of the Speedster-EXD550 has been done by the Penn State High Energy Astrophysics Detector and Instrumentation lab in both full-frame and event-driven readout modes. A radioactive 55Fe source was used for the measurements presented. Here, we discuss the methods and recent results for the characterization of the Speedster-EXD550 dark current, read noise, gain, and gain variation.
Next-generation x-ray observatories, such as the Lynx X-ray Observatory Mission Concept or other similar concepts in the coming decade, will require detectors with high quantum efficiency (QE) across the soft x-ray band to observe the faint objects that drive their mission science objectives. Hybrid CMOS detectors (HCDs), a form of active-pixel sensor, are promising candidates for use on these missions because of their fast read-out, low power consumption, and intrinsic radiation hardness. We present QE measurements of a Teledyne H2RG HCD, performed using a gas-flow proportional counter as a reference detector. We find that this detector achieves high QE across the soft x-ray band, with an effective QE of 94.6 ± 1.1 % at the Mn Kα / Kβ energies (5.90/6.49 keV), 98.3 ± 1.9 % at the Al Kα energy (1.49 keV), 85.6 ± 2.8 % at the O Kα energy (0.52 keV), and 61.3 ± 1.1 % at the C Kα energy (0.28 keV). These values are in good agreement with our model, based on the absorption of detector layers. We find similar results in a more restrictive analysis considering only high-quality events, with only somewhat reduced QE at lower energies.
Next-generation X-ray observatories, such as the Lynx X-ray Observatory Mission Concept, will require detectors with high quantum efficiency (QE) across the soft X-ray band to observe the faint objects that drive their mission science cases. Hybrid CMOS Detectors (HCDs), a form of active-pixel sensor, are promising candidates for use on these missions because of their faster read-out, lower power consumption, and greater radiation hardness than detectors used in the current generation of X-ray telescopes. In this work, we present QE measurements of a Teledyne H2RG HCD. These measurements were performed using a gas-flow proportional counter as a reference detector to measure the absolute flux incident on the HCD. We find an effective QE of 95:0 ± 1:1% at the Mn ∝/Kβ lines (at 5.9 and 6.5 keV), 98:5 ± 1:8% at the Al Ka line (1.5 keV), and 85:0 ± 2:8% at the O K∝ line (0.52 keV).
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