We report the results of an extensive set of simulations exploring the sensitivity of the BlackCAT CubeSat to long-duration gamma-ray bursts (GRBs). BlackCAT is a NASA APRA-funded CubeSat mission for the detection and real-time subarcminute localization of high-redshift ( z ≳ 3.5) GRBs. Thanks to their luminous and long-lived afterglow emissions, GRBs are uniquely valuable probes of high-redshift star-forming galaxies and the intergalactic medium. In addition, each detected GRB with a known redshift serves to localize a region of high-redshift star formation in three dimensions, enabling deep follow-on searches for host galaxies and associated local and large-scale structures. We explore two distinct models for the GRB redshift distribution and luminosity function, both consistent with Swift observations. We find that, for either model, BlackCAT is expected to detect a mean of 42 bursts per year on orbit, with 6.7% to 10% of these at z > 3.5. BlackCAT bursts will be localized to an r _90 ≲ 55″ precision and reported to the community within seconds. Due to the mission orbit and pointing scheme, bursts will be located in the night sky and well placed for deep multiwavelength follow-up observations. BlackCAT is on schedule to achieve launch readiness in 2025.

BlackCAT is a NASA-funded 6U CubeSat mission planned to be launch-ready in 2025. BlackCAT will use its wide field-of-view and arcminute-scale localization to identify gamma-ray bursts (GRBs), gravitational-wave counterparts, and other high-energy transient events. The mission will send rapid alerts after detection of a transient event, enabling prompt follow-up from other ground- and space-based observatories. The science instrument is a coded aperture telescope, using a focal plane with four Speedster-EXD550 event-driven X-ray hybrid CMOS detectors (HCDs) and a gold-plated nickel coded mask to localize source positions. We describe methods for the calibration of the detectors and the assembled coded-aperture instrument. We also briefly discuss plans for in-flight commissioning and calibration.

The BlackCAT CubeSat is an X-ray coded-aperture-telescope observatory that is expected to launch in 2025. It is designed for observations of bright X-ray sources in the 0.5-20 keV band. The instrument will have a wide field of view (0.85 steradian) and be capable of catching gamma ray bursts (GRBs) from the distant universe, galactic transients, and flares from blazars, while monitoring the X-ray sky. In addition to the primary high-redshift GRB science, BlackCAT can monitor known source variability and search for rare and exciting events including gravitational-wave X-ray counterparts, magnetar flares, supernova shock breakouts, and tidal disruption events. The mission will thus function as a multi-wavelength and multi-messenger complement to present and future facilities including LIGO, VIRGO, KAGRA, IceCube, KM3NET, LSST, LOFAR, SKA, and CTA. Rapid notifications of burst positions will be transmitted to the ground via satellite network and then relayed to the GCN. The name BlackCAT is derived from its scientific emphasis on black-hole-related transient events being observed with a coded aperture telescope (CAT). BlackCAT will serve as the scientific payload aboard a commercial 6U CubeSat spacecraft provided by NanoAvionics US. Novel event-driven X-ray hybrid CMOS detectors will form the focal plane array. In addition to carrying out science programs related to distant GRBs, transients, and X-ray sky monitoring, BlackCAT will also serve as a pathfinder for future economical missions combining multiple BlackCAT modules on either a single small satellite or on multiple CubeSats. BlackCAT will also serve as a platform for new X-ray hybrid CMOS detector development. An overview of BlackCAT in its current development state and its current status will be presented.

The Penn State University High-Energy Astrophysics Detector and Instrumentation (HEADI) Lab, in collaboration with Teledyne Imaging Sensors (TIS), has continued its efforts to improve soft x-ray Hybrid CMOS detectors (HCDs) on several fronts. We report on the read noise and energy resolution for the H1RG and the H2RG using a cryogenic SIDECAR (TM), which gained TRL 9 and flight heritage through the Water Recovery X-ray Rocket Mission in 2018. We also describe the 40-mu m event-driven Speedster-EXD HCD, which has been scaled up from a 64x64 array to an 550x550 array. The readout circuitry within the ROIC for the Speedster-EXD contains a high-gain capacitive transimpedance amplifier (CTIA) to negate pixel cross-talk, in-pixel correlated double sampling (CDS) for correction of reset noise variations, and an in-pixel comparator enabling event-driven readout. Here we report on read noise and energy resolution measurements for the Speedster-EXD and discuss the upcoming BlackCAT CubeSAT, on which the Speedster-EXD550 will fly, raising the TRL of these HCDs. Further, to meet the requirements of future high-throughput and high spatial resolution Lynx-like x-ray observatories, HCDs with fast readout and small pixel sizes have been developed. Here we report on the energy resolution and the lowest measured read noise of any x-ray HCD to-date for the 12.5-mu m 128x128 prototype Small-pixel HCD, as well as present the current results for the newest x-ray HCD, the Small-pixel1024. The Small-pixel1024 is a 12.5 mu m 1024x1024 HCD utilizing a high-gain CTIA and in-pixel CDS. Finally, we report on the development efforts between Penn State and Teledyne on a new event-driven HCD, which will retain the low read noise of the Small-pixel HCD while having event-driven capabilities like the Speedster-EXD.

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 (CCDs) 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 also improving performance in other respects like 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 (CMOS) detectors capable of event-driven readout, developed by Teledyne Imaging Sensors and Penn State University. We present 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.

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.

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.

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. In this work, 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.

We conduct X-ray spectral fits on 184 likely counterparts to Fermi-LAT 3FGL unassociated sources. Characterization and classification of these sources allows for more complete population studies of the high-energy sky. Most of these X-ray spectra are well fit by an absorbed power-law model, as expected for a population dominated by blazars and pulsars. A small subset of seven X-ray sources have spectra unlike the power law expected from a blazar or pulsar and may be linked to coincident stars or background emission. We develop a multiwavelength machine learning classifier to categorize unassociated sources into pulsars and blazars using gamma-ray and X-ray observations. Training a random forest (RF) procedure with known pulsars and blazars, we achieve a cross-validated classification accuracy of 98.6%. Applying the RF routine to the unassociated sources returned 126 likely blazar candidates (defined as P-bzr >= 90%) and five likely pulsar candidates (P-bzr <= 10%). Our new X-ray spectral analysis does not drastically alter the RF classifications of these sources compared to previous works, but it builds a more robust classification scheme and highlights the importance of X-ray spectral fitting. Our procedure can be further expanded with UV, visual, or radio spectral parameters or by measuring flux variability.