The BlackCAT observatory makes use of a 6U CubeSat platform with an x-ray coded aperture telescope payload. BlackCAT, utilizing its wide field-of-view (0.9 steradians), will monitor deep space for a variety of x-ray transients and flares, with a primary focus on high redshift gamma-ray bursts. The payload consists of a detector module (DM), a dedicated electronics package, mechanical mounts, and thermal straps for passive cooling. The DM includes the DM housing, coded aperture mask, optical blocking filter (OBF), and a focal plane array (FPA) consisting of four x-ray hybrid CMOS detectors (HCDs). Each of these four detectors is a 550×550-pixel Speedster-EXD silicon sensor with a molybdenum package to provide a low-strain thermal and mechanical mounting structure. The primary purpose of the electronics package is reading out and processing data from the HCDs. For optimal scientific performance, the FPA must be maintained at a temperature of -40°C or below. The detectors have an aluminum OBF directly deposited because the silicon detectors are sensitive to optical light. For additional optical blocking against the brightest optical background and UV light, a separate OBF will be mounted in front of the detector surface. The coded aperture mask is a wire mesh made of nickel with a thin layer of gold coating all sides. The mask allows approximately 40% of incident x-rays to strike the detector in a unique pattern that is dependent upon source position and the open cell geometry. This allows for the angular position of the source to be determined to sub-arcminute precision. To prevent deformation due to thermal strain, the mask is required to maintain a set temperature between 10°C and 20°C. The DM housing acts as the primary support structure for the payload and is thick enough to provide shielding from off-axis x-rays and optical/UV light. The OBF is directly connected to the DM housing, while the mask and FPA are both thermally isolated via standoffs to meet respective temperature requirements. Additionally, the DM housing is the interface between the payload components and the chassis. We present an overview of the mechanical and thermal payload requirements, as well as design constraints imposed by the 6U CubeSat form factor. We describe the designs used to meet these requirements and present analyses to demonstrate the efficacy of these designs. The mechanical requirements and information from thermal analyses will drive the overall design of the BlackCAT CubeSat to achieve the science goals throughout the mission lifetime.
The BlackCAT CubeSat will monitor the soft x-ray sky, searching for high-redshift gamma-ray bursts (GRBs), gravitational-wave counterparts, and other high-energy transient events. BlackCAT will utilize a coded-aperture mask to localize sources to sub-arcminute precision. We investigate the primary forms of background that will affect this mission and present different methods to suppress these sources in order to increase the sensitivity of this mission. In the absence of mitigation, the optical and ultraviolet backgrounds could increase noise in the hybrid CMOS detectors (HCDs) used in this mission and potentially trigger spurious events. We plan to use a polyimide filter to suppress extreme ultraviolet emission produced by the geocorona. The HCDs and polyimide filter will be coated with a thin aluminum layer to block optical light. We estimate the magnitude of the observed cosmic and galactic X-ray backgrounds. Additionally, we investigate the impact of trapped particles on the sensitivity and duty cycle of the mission. We discuss the effect of these various sources of background on the sensitivity of BlackCAT to GRBs and other transient events.
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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