arXiv subjects

Catherine E. Grant

Publications and source records attributed to Catherine E. Grant.

At least 19 recordsLinked to original sources

arXiv2026

Curving X-ray detectors for astrophysics applications

Next-generation X-ray optics will revolutionize high-energy astrophysics, yet they present several challenges to design a complementary focal plane. In particular, the focal surface is curved, requiring many small, flat sensors to achieve a large field. We present work building on MIT Lincoln Laboratory technology to curve the sensor itself, improving image quality and reducing complexity. Applying this technology to back-illuminated, large-format CCDs having well-characterized X-ray response, we describe the process and report success curving functional BI CCDs to a 2.5-m radius of curvature, achieving RMS curvature deviations less than 1 micron. We confirm that there is no appreciable increase in dark current and that the spectroscopic performance across the 0.3-6 keV band remains excellent. These results demonstrate that curved, large-format X-ray sensors are realizable, and the process can be extended to silicon detectors with other architectures, including active pixel sensors.

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arXiv2026

X-ray grating spectroscopy as a mission enhancement

We propose to add instruments to any potential future X-ray mission with focussing optics that is considered in NASA's ASTRA framework. Such an instrument is a necessity to study AGN wind outflows and feedback, find the missing baryons, study the intergalactic medium, and analyze abundances and chemical bonds in dust grains throughout the Milky Way. We conclude that those science goals can be achieved with a spectral resolving power > 3000 in the soft X-ray band (about 10-40 Ang) and an effective area a few times larger than current instruments. We describe a possible mission implementation for a soft X-ray grating spectrometer that can be folded in and out or be mounted permanently in the beam. Such an instrument can reach the requirements for a wide variety of host mission properties. A small UV imager and a UV spectrograph can be mounted on the same platform with independent optics. These added instruments vastly enhance the science capabilities of the host mission for a modest cost (100-200 million $) and with weight and power needs that can be easily accommodated in any major mission.

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arXiv2026

Fast, low noise, megapixel detector and readout systems for future X-ray astronomy missions

Next-generation strategic X-ray astronomy missions will require the simultaneous achievement of high angular resolution, large effective collecting area, and wide-field imaging with large-format focal plane detectors. Realizing the associated science objectives--ranging from precision measurements of bright point sources to the detection and characterization of faint diffuse emission-places stringent and, in some cases, competing requirements on detector performance. In particular, high frame rates are necessary to mitigate photon pile-up in observations of bright sources and to reduce contamination from particle-induced background in measurements of low surface brightness structures. At the same time, these instruments must preserve excellent soft X-ray response, which places tight constraints on read noise and on the fidelity of event characterization. State-of-the-art X-ray charge-coupled devices (CCDs) approach many of the key performance metrics required for these missions, but readout speed remains a primary limitation. Addressing this gap requires readout architectures that scale to high channel count, sustain high pixel throughput, and preserve the low-noise characteristics needed for soft X-ray sensitivity.

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arXiv2026

High-speed, low-noise, multi-megapixel CCDs for next generation X-ray observatories

Next generation X-ray observatories require fast, low-noise, low-power, multi-megapixel imaging spectrometers. To meet these demands, the X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, in partnership with the MIT Kavli Institute and MIT Lincoln Laboratory (MIT-LL), is developing multi-channel X-ray charge-coupled devices (CCDs) and fast readout architectures. We report the energy resolution and noise performance achieved with a full-scale (1440x1440-pixel), 16-channel, front-illuminated MIT-LL CCD detector developed for the Advanced X-ray Imaging Satellite (AXIS) concept, the CCID-100, read out using two Multi-Channel Readout Chip (MCRC) V1 application-specific integrated circuit (ASIC) chips in the new Stanford CCID-100 test setup. We describe an automated method for bias optimization on each CCD channel, and integrated debugging features of the front-end ASIC and readout system. The demonstrated performance confirms that these systems can meet the speed and noise requirements of future strategic X-ray missions.

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arXiv2026

High-statistics simulations of NewAthena WFI background using Geant4

The observation of hot gas structures is one science goal of the Wide Field Imager (WFI) on ESA's NewAthena X-ray observatory. Because the measurement of these faint diffuse sources is limited by background from cosmic ray particle interactions within the instrument, understanding and reducing this background is critical. To this end, we employ a two-pronged approach, performing high-fidelity Geant4 simulations on both detailed, realistic geometry models as well as complementary simple geometry models. The former can reveal subtle sensitivities of background to details of the instrument design. The latter allows for fast iteration, useful in guiding and understanding the larger simulations. We show how we leverage High Performance Computing (HPC) resources to achieve simultaneously high throughput and fast time to result. We discuss our recent results, which are applicable not only to WFI, but also other X-ray missions.

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arXiv2026

Output-Stage Design Optimization for High-Sensitivity SiSeRO CCDs and SiSeRO Active Pixel Sensors

The Single electron Sensitive Read Out (SiSeRO) technology is a new device class designed to support the needs of future X-ray and optical astronomical telescopes that will require fast, low-noise, megapixel spectro-imagers. Developed at MIT Lincoln Laboratory, in collaboration with Stanford University and MIT, the first generation SiSeRO-CCD (charge-coupled device) prototypes achieved a charge/current conversion gain of 700$-$800 pA per electron, an equivalent noise charge (ENC) of around 3.5 electrons root mean square (RMS), and a full width half maximum (FWHM) energy resolution of approximately 130 eV at 5.9 keV at a readout speed of 625 kpix/s. Utilizing Repetitive Non-Destructive Readout (RNDR), these same devices also demonstrated sub-electron noise performance (ENC$<$0.5 electrons RMS) at a readout speed of 10 kpix/s. We present the results of device simulations for next-generation SiSeRO CCD output stages that optimize the sensing transistor and its internal gate geometry to enhance noise and speed performance. Further, the goal is to develop a SiSeRO active pixel sensor (APS) that combines the proven X-ray performance of CCDs with the architectural advantages of an APS. Enabling this requires substantial design updates, for example, incorporating two SiSeRO amplifiers side by side on each pixel and shuffling the charge between them to support RNDR. We discuss our device simulation framework and design parameter optimization in the first-generation SiSeRO devices.

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arXiv2026

Fast, low-noise CCD systems for future strategic X-ray missions

Future strategic X-ray missions, such as those targeted by the Great Observatories Maturation Program (GOMaP), require fast, low-noise X-ray imaging spectrometers. To achieve the speed and noise capabilities required by such programs, our Stanford team, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing enhanced X-ray charge-coupled devices (CCDs) and readout systems that leverage tailored application-specific integrated circuits (ASICs). Here, we report the energy resolution and noise performance achieved using some of the latest MIT-LL CCDs in conjunction with Stanford-developed Multi-Channel Readout Chip (MCRC) ASICs. Additionally, we present a new sampling method for simultaneous optimization of the output gate (OG), reset gate (RG), and reset drain (RD) biases which, in combination with new integrated fast summing well (SW) and RG clock operation modes, enables the data rates and noise required for future X-ray telescopes. Finally, we present noise power spectral density (PSD) and waveform analysis methods and posit a physical model for characterizing and understanding output stage noise behavior.

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arXiv2026

The High-Speed FPGA Readout System for the Advanced X-ray Imaging Satellite (AXIS)

The Advanced X-ray Imaging Satellite (AXIS) is a Probe-class mission concept designed to deliver arcsecond spatial resolution, high-sensitivity spectral imaging across the 0.3-10 keV band. The X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing the AXIS X-ray camera, including both the detector and the front-end readout electronics required to meet the mission's demanding performance goals. The telescope's focal plane detector consists of four 1440x1440 pixel charge-coupled devices (CCDs) developed by MIT-LL, each featuring 16 parallel output channels. These outputs are amplified by a high-speed, low-power, low-noise application-specific integrated circuit (ASIC) - the Multi-Channel Readout Chip (MCRC) - developed at Stanford. Following amplification, the analog signals are digitized and processed to construct a pixel array, prior to event detection. Here, we present the field-programmable gate array (FPGA) architecture developed to enable high-speed, parallelized readout of these CCD channels. The FPGA samples 16 analog-to-digital converter (ADC) channels at 50 MHz, performs preprocessing of pixel data, which is then streamed via User Datagram Protocol (UDP) over a 1 Gb Ethernet link to the back-end system for event reconstruction. Our design demonstrates the goal readout performance for AXIS (20 frames per second) and provides a framework for future high-throughput X-ray observatories.

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arXiv2026

RNDR noise modeling in first-generation Single electron Sensitive Readout (SiSeRO) devices

Flagship observatories require single-photon detectors with ultra-fast readout, sub-electron noise performance, and scalable large-format architectures. The X-ray Astronomy and Observational Cosmology group at Stanford, in collaboration with the MIT Kavli Institute and MIT Lincoln Laboratory, is developing readout technologies for next-generation detectors. Prototypes employing Single-electron Sensitive Readout (SiSeRO) amplifiers demonstrate excellent read noise and spectral performance using repetitive non-destructive readout (RNDR), achieving 0.5 e$^-$ noise in under 57 cycles. We have modeled noise for longer RNDR cycles, exploring probabilistic mechanisms such as thermal leakage and impact ionization. Here we present our model results, including statistical limits on dark current-like signals. Maturation of SiSeRO technology will improve detector performance at soft X-ray energies, addressing technology gaps for future X-ray and UV/visible/near-IR observatories.

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arXiv2026

First results for second generation SiSeRO CCD devices

The Astro2020 Decadal recommended the development of a suite of next generation astronomical observatories spanning the X-ray to near-IR spectrum. These programs require fast, extremely low noise detectors to fulfill their science goals. To address this technology gap, Stanford X-ray Astronomy and Observational Cosmology (XOC) group, MIT Lincoln Laboratory (MIT-LL), and MIT Kavli Institute (MKI) are advancing Single electron Sensitive Read Out (SiSeRO), a multiband detector technology capable of achieving substantially sub-electron noise via Repetitive Non-Destructive Readout (RNDR). We present initial results for our second generation SiSeRO CCDs. We also discuss our test bed, including a readout electronics system capable of accommodating all second-generation SiSeRO CCD variants utilizing the XOC-designed Multi-Channel Readout Chip (MCRC) ASIC.

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arXiv2026

XRISM Observations of Abell 1795: Evidence for Low Turbulence and Resonant Scattering

We present high-resolution X-ray spectroscopic observations of the cool-core galaxy cluster Abell~1795 obtained with XRISM/Resolve. The cluster was observed with two deep pointings: a 225 ks central exposure and a 113 ks northern exposure, extending to a projected radius of 320 kpc from the cluster center. Single-temperature fits reveal a clear radial gradient in the line-of-sight velocity dispersion, decreasing from 114 $\pm$ 11 km/s in the core to 68 $\pm$ 39 km/s at 320 kpc. The bulk velocities in the central regions are very low (22 $\pm$ 12 and 7 $\pm$ 21 km/s), indicating no significant relative motion between the brightest cluster galaxy (BCG) and the intracluster medium (ICM). Given that the central region includes the southward extending cool gas tail, this result disfavors the ``cooling-wake'' scenario and instead supports an AGN-uplift origin. We find that the nonthermal pressure fraction decreases with radius, from $P_{\rm NT}/P_{\rm T}\approx2\%$ in the core to $\sim0.6\%$ at 330 kpc, suggesting that the northern ICM of A1795 is largely quiescent. Two-temperature and split energy-band (2--4 keV and 6--7 keV) fits identify two gas phases within the central $<1.5'$ region, providing strong evidence for multiphase gas in the cluster core. We detect a $\sim14\%$ resonant suppression of the optically thick Fe XXV $w$ line in the center. Additionally, we observe a significant excess in the Fe XXV $y$ line-flux relative to models. Accounting for uncertainties in the atomic data reduces this discrepancy, suggesting that atomic data uncertainties may contribute to the observed residual flux.

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arXiv2025

The high-speed X-ray camera on AXIS: design and performance updates

AXIS, a Probe mission concept now in a Phase A study, will provide transformative studies of high-energy astrophysical phenomena thanks to its high-resolution X-ray spectral imaging. These capabilities are enabled by improvements to the mirror design that greatly increase the X-ray throughput per unit mass; and to the detector system, which operates more than an order of magnitude faster than heritage instruments while maintaining excellent spectral performance. We present updates to the design of the AXIS High-Speed Camera, a collaborative effort by MIT, Stanford University, the Pennsylvania State University, and the Southwest Research Institute. The camera employs large-format MIT Lincoln Laboratory CCDs that feature multiple high-speed, low-noise output amplifiers and an advanced single-layer polysilicon gate structure for fast, low-power clock transfers. A first lot of prototype CCID100 CCDs has completed fabrication and will soon begin X-ray performance testing. The CCDs are paired with high-speed, low-noise ASIC readout chips designed by Stanford to provide better performance than conventional discrete solutions at a fraction of the power consumption and footprint. Complementary Front-End Electronics employ state-of-the-art digital video waveform capture and advanced signal processing to further deliver low noise at high speed. The Back-End Electronics provide high-speed identification of candidate X-ray events and transient monitoring that relays fast alerts of changing sources to the community. We highlight updates to our parallel X-ray performance test facilities at MIT and Stanford, and review the current performance of the CCD and ASIC technology from testing of prototype devices. These measurements achieve excellent spectral response at the required readout rate, demonstrating that we will meet mission requirements and enable AXIS to achieve world-class science.

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arXiv2025

Development and testing of integrated readout electronics for next generation SiSeRO (Single electron Sensitive Read Out) devices

The first generation of Single electron Sensitive Read Out (SiSeRO) amplifiers, employed as on-chip charge detectors for charge-coupled devices (CCDs) have demonstrated excellent noise and spectral performance: a responsivity of around 800 pA per electron, an equivalent noise charge (ENC) of 3.2 electrons root mean square (RMS), and a full width half maximum (FWHM) energy resolution of 130 eV at 5.9 keV for a readout speed of 625 Kpixel/s. Repetitive Non Destructive Readout (RNDR) has also been demonstrated with these devices, achieving an improved ENC performance of 0.36 electrons RMS after 200 RNDR cycles. In order to mature this technology further, Stanford University, in collaboration with MIT Kavli Institute and MIT Lincoln Laboratory, are developing new SiSeRO detectors with improved geometries that should enable greater responsivity and improved noise performance. These include CCD devices employing arrays of SiSeRO amplifiers to optimize high speed, low noise RNDR readout and a proof-of-concept SiSeRO active pixel sensor (APS). To read out these devices, our team has developed a compact, 8-channel, fast, low noise, low power application specific integrated circuit (ASIC) denoted the Multi-Channel Readout Chip (MCRC) that includes an experimental drain current readout mode intended for SiSeRO devices. In this paper, we present results from the first tests of SiSeRO CCD devices operating with MCRC readout, and our designs for next generation SiSeRO devices.

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arXiv2025

Fast, low noise CCD systems for future strategic x-ray missions

Future strategic X-ray missions, such as the Advanced X-ray Imaging Satellite (AXIS) and those targeted by the Great Observatories Maturation Program (GOMaP), require fast, low-noise X-ray imaging spectrometers. To achieve the speed and noise capabilities required by such programs, the X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, in collaboration with the MIT Kavli Institute (MKI) and MIT Lincoln Laboratory (MIT-LL), is developing readout systems that leverage the high speed, low noise, and low power consumption of application-specific integrated circuit (ASIC) devices. Here, we report the energy resolution and noise performance achieved using MIT-LL AXIS prototype charge-coupled device (CCD) detectors in conjunction with Stanford-developed Multi-Channel Readout Chip (MCRC) ASICs. Additionally, we present a new sampling method for simultaneous optimization of the output gate (OG), reset gate (RG), and reset drain (RD) biases which, in combination with new integrated fast summing well (SW) and RG clock operation modes, enables the data rates required of future X-ray telescopes.

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arXiv2025

Ground calibration plans for the AXIS high speed camera

The Advanced X-ray Imaging Satellite (AXIS), an astrophysics NASA probe mission currently in phase A, will provide high-throughput, high-spatial resolution X-ray imaging in the 0.3 to 10 keV band. We report on the notional ground calibration plan for the High Speed Camera on AXIS, which is being developed at the MIT Kavli Institute for Astrophysics and Space Research using state-of-the-art CCDs provided by MIT Lincoln Laboratory in combination with an integrated, high-speed ASIC readout chip from Stanford University. AXIS camera ground calibration draws on previous experience with X-ray CCD focal plans, in particular Chandra/ACIS and Suzaku/XIS, utilizing mono-energetic X-ray line sources to measure spectral resolution and quantum efficiency. Relative quantum efficiency of the CCDs will be measured against an sCMOS device, with known absolute calibration from synchrotron measurements. We walk through the envisioned CCD calibration pipeline and we discuss the observatory-level science and calibration requirements and how they inform the camera calibration.

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arXiv2025

Design, development, and commissioning of a flexible test setup for the AXIS prototype detector

The Advanced X-ray Imaging Satellite (AXIS) is one of two candidate mission concepts selected for Phase-A study for the new NASA Astrophysics Probe Explorer (APEX) mission class, with a planned launch in 2032. The X-ray camera for AXIS is under joint development by the X-ray Astronomy and Observational Cosmology (XOC) Group at Stanford, the MIT Kavli Institute (MKI), and MIT Lincoln Laboratory (MIT-LL). To accelerate development efforts and meet the AXIS mission requirements, XOC has developed a twin beamline testing system, capable of providing the necessary performance, flexibility, and robustness. We present design details, simulations, and performance results for the newer of the two beamlines, constructed and optimized to test and characterize the first full-size MIT-LL AXIS prototype detectors, operating with the Stanford-developed Multi-Channel Readout Chip (MCRC) integrated readout electronics system. The XOC X-ray beamline design is forward-looking and flexible, with a modular structure adaptable to a wide range of detector technologies identified by the Great Observatories Maturation Program (GOMAP) that span the X-ray to near-infrared wavelengths.

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arXiv2025

Constraints on Non-Thermal Pressure at galaxy cluster outskirts from a Joint SPT and XMM-Newton Analysis

We present joint South Pole Telescope (SPT) and XMM-Newton observations of 8 massive galaxy clusters (0.8--1.7$\times$10$^{15}$ M$_{\odot}$) spanning a redshift range of 0.16 to 0.35. Employing a novel SZ+X-ray fitting technique, we effectively constrain the thermodynamic properties of these clusters out to the virial radius. The resulting best-fit electron density, deprojected temperature, and deprojected pressure profiles are in good agreement with previous observations of massive clusters. For the majority of the cluster sample (5 out of 8 clusters), the entropy profiles exhibit a self-similar behavior near the virial radius. We further derive hydrostatic mass, gas mass, and gas fraction profiles for all clusters up to the virial radius. Comparing the enclosed gas fraction profiles with the universal gas fraction profile, we obtain non-thermal pressure fraction profiles for our cluster sample at $>$$R_{500}$, demonstrating a steeper increase between $R_{500}$ and $R_{200}$ that is consistent with the hydrodynamical simulations. Our analysis yields non-thermal pressure fraction ranges of 8--28% (median: 15 $\pm$ 11%) at $R_{500}$ and 21--35% (median: 27 $\pm$ 12%) at $R_{200}$. Notably, weak-lensing mass measurements are available for only four clusters in our sample, and our recovered total cluster masses, after accounting for non-thermal pressure, are consistent with these measurements.

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arXiv2025

Using the XMM-Newton small window mode to investigate systematic uncertainties in the particle background of X-ray charge-coupled device detectors

The level and uncertainty of the particle induced background in CCD detectors plays a crucial role for future X-ray instruments, such as the Wide Field Imager (WFI) onboard Athena. To mitigate the background systematic uncertainties, which will limit the Athena science goals, we aim to understand the relationship between the energetic charged particles interacting in the detector and satellite, and the instrumental science background to an unprecedented level. These particles produce easily identified "cosmic-ray tracks" along with less easily identified signals produced by secondary particles, e.g., X-rays generated by particle interactions with the instrument and indistinguishable from genuine sky X-rays. We utilize the Small Window Mode of the PN camera onboard XMM-Newton to understand the time, spatial and energy dependence of the various background components, particularly the particle induced background. While the distribution of particle events follows expected detector readout patterns, we find a particle track length distribution inconsistent with the simple, isotropic model. We also find that the detector mode-specific readout results in a shifted Cu fluorescent line. We illustrate that on long timescales the variability of the particle background correlates well with the solar cycle. This 20-year lightcurve, can be reproduced by a particle detector onboard Chandra, the HRC anti-coincidence shield. We conclude that the self-anti-coincidence method of removing X-ray-like events near detected particle tracks in the same frame can be optimized with the inclusion of additional information, such as the energy of the X-ray. The results presented here are relevant for any future pixelated X-ray imaging detector, and could allow the WFI to probe to truly faint X-ray surface brightness.

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