Lynx is a concept under study for prioritization in the 2020 Astrophysics Decadal Survey. Providing orders of magnitude increase in sensitivity over Chandra, Lynx will examine the first black holes and their galaxies, map the large-scale structure and galactic halos, and shed new light on the environments of young stars and their planetary systems. In order to meet the Lynx science goals, the telescope consists of a high-angular resolution optical assembly complemented by an instrument suite that may include a High Definition X-ray Imager, X-ray Microcalorimeter and an X-ray Grating Spectrometer. The telescope is integrated onto the spacecraft to form a comprehensive observatory concept. Progress on the formulation of the Lynx telescope and observatory configuration is reported in this paper.
The Penn State X-ray detector lab, in collaboration with Teledyne Imaging Sensors (TIS), have progressed their efforts to improve soft X-ray Hybrid CMOS detector (HCD) technology on multiple fronts. Having newly acquired a Teledyne cryogenic SIDECARTM ASIC for use with HxRG devices, measurements were performed with an H2RG HCD and the cooled SIDECARTM. We report new energy resolution and read noise measurements, which show a significant improvement over room temperature SIDECARTM operation. Further, in order to meet the demands of future high-throughput and high spatial resolution X-ray observatories, detectors with fast readout and small pixel sizes are being developed. We report on characteristics of new X-ray HCDs with 12.5 micron pitch that include in-pixel CDS circuitry and crosstalk-eliminating CTIA amplifiers. In addition, PSU and TIS are developing a new large-scale array Speedster-EXD device. The original 64 × 64 pixel Speedster-EXD prototype used comparators in each pixel to enable event driven readout with order of magnitude higher effective readout rates, which will now be implemented in a 550 × 550 pixel device. Finally, the detector lab is involved in a sounding rocket mission that is slated to fly in 2018 with an off-plane reflection grating array and an H2RG X-ray HCD. We report on the planned detector configuration for this mission, which will increase the NASA technology readiness level of X-ray HCDs to TRL 9.
Arcus, a Medium Explorer (MIDEX) mission, was selected by NASA for a Phase A study in August 2017. The observatory provides high-resolution soft X-ray spectroscopy in the 12-50Å bandpass with unprecedented sensitivity: effective areas of >450 cm2 and spectral resolution >2500. The Arcus key science goals are (1) to measure the effects of structure formation imprinted upon the hot baryons that are predicted to lie in extended halos around galaxies, groups, and clusters, (2) to trace the propagation of outflowing mass, energy, and momentum from the vicinity of the black hole to extragalactic scales as a measure of their feedback and (3) to explore how stars, circumstellar disks and exoplanet atmospheres form and evolve. Arcus relies upon the same 12m focal length grazing-incidence silicon pore X-ray optics (SPO) that ESA has developed for the Athena mission; the focal length is achieved on orbit via an extendable optical bench. The focused X-rays from these optics are diffracted by high-efficiency Critical-Angle Transmission (CAT) gratings, and the results are imaged with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. Mission operations are straightforward, as most observations will be long (~100 ksec), uninterrupted, and pre-planned, although there will be capabilities to observe sources such as tidal disruption events or supernovae with a ~3 day turnaround. Following the 2nd year of operation, Arcus will transition to a proposal-driven guest observatory facility.
The Water Recovery X-ray Rocket (WRXR) is a sounding rocket payload that will launch from the Kwajalein Atoll in April 2018 and seeks to be the first astrophysics sounding rocket payload to be water recovered by NASA. WRXR's primary instrument is a grating spectrometer that consists of a mechanical collimator, X-ray reflection gratings, grazing-incidence mirrors, and a hybrid CMOS detector. The instrument will obtain a spectrum of the diffuse soft X-ray emission from the northern part of the Vela supernova remnant and is optimized for 3rd and 4th order OVII emission. Utilizing a field of view of 3.25° × 3.25° and resolving power of λ/δλ ≈40-50 in the lines of interest, the WRXR spectrometer aims to achieve the most highly-resolved spectrum of Vela's diffuse soft X-ray emission. This paper presents introductions to the payload and the science target.
Arcus will be proposed to the NASA Explorer program as a free-flying satellite mission that will enable high-resolution soft X-ray spectroscopy (8-50) with unprecedented sensitivity – effective areas of >500 sq cm and spectral resolution >2500. The Arcus key science goals are (1) to determine how baryons cycle in and out of galaxies by measuring the effects of structure formation imprinted upon the hot gas that is predicted to lie in extended halos around galaxies, groups, and clusters, (2) to determine how black holes influence their surroundings by tracing the propagation of out-flowing mass, energy and momentum from the vicinity of the black hole out to large scales and (3) to understand how accretion forms and evolves stars and circumstellar disks by observing hot infalling and outflowing gas in these systems. Arcus relies upon grazing-incidence silicon pore X-ray optics with the same 12m focal length (achieved using an extendable optical bench) that will be used for the ESA Athena mission. The focused X-rays from these optics will then be diffracted by high-efficiency off-plane reflection gratings that have already been demonstrated on sub-orbital rocket flights, imaging the results with flight-proven CCD detectors and electronics. The power and telemetry requirements on the spacecraft are modest. The majority of mission operations will not be complex, as most observations will be long (~100 ksec), uninterrupted, and pre-planned, although there will be limited capabilities to observe targets of opportunity, such as tidal disruption events or supernovae with a 3-5 day turnaround. After the end of prime science, we plan to allow guest observations to maximize the science return of Arcus to the community.
Future X-ray astronomy observatories will employ high-speed silicon-based active pixel sensors to obtain wide fields of view with good radiation hardness and low levels of detector saturation (pileup). Detector readout rates envisioned for missions such as Athena and X-ray Surveyor are far too high for existing software-based event recognition techniques to be able to extract the X-ray events from the data stream. We report on the development of high-speed event recognition electronics tailored to the requirements of these new detectors.
The Speedster-EXD is a new 64×64 pixel2, 40-μm pixel pitch, 100-μm depletion depth hybrid CMOS x-ray detector with the capability of reading out only those pixels containing event charge, thus enabling fast effective frame rates. A global charge threshold can be specified, and pixels containing charge above this threshold are flagged and read out. The Speedster detector has also been designed with other advanced in-pixel features to improve performance, including a low-noise, high-gain capacitive transimpedance amplifier that eliminates interpixel capacitance crosstalk (IPC), and in-pixel correlated double sampling subtraction to reduce reset noise. We measure the best energy resolution on the Speedster-EXD detector to be 206 eV (3.5%) at 5.89 keV and 172 eV (10.0%) at 1.49 keV. The average IPC to the four adjacent pixels is measured to be 0.25%±0.2% (i.e., consistent with zero). The pixel-to-pixel gain variation is measured to be 0.80%±0.03%, and a Monte Carlo simulation is applied to better characterize the contributions to the energy resolution.
NASA's Chandra X-ray Observatory continues to provide an unparalleled means for exploring the high-energy universe. With its half-arcsecond angular resolution, Chandra studies have deepened our understanding of galaxy clusters, active galactic nuclei, galaxies, supernova remnants, neutron stars, black holes, and solar system objects. As we look beyond Chandra, it is clear that comparable or even better angular resolution with greatly increased photon throughput is essential to address ever more demanding science questions—such as the formation and growth of black hole seeds at very high redshifts; the emergence of the first galaxy groups; and details of feedback over a large range of scales from galaxies to galaxy clusters. Recently, we initiated a concept study for such a mission, dubbed X-ray Surveyor. The X-ray Surveyor strawman payload is comprised of a high-resolution mirror assembly and an instrument set, which may include an X-ray microcalorimeter, a high-definition imager, and a dispersive grating spectrometer and its readout. The mirror assembly will consist of highly nested, thin, grazing-incidence mirrors, for which a number of technical approaches are currently under development—including adjustable X-ray optics, differential deposition, and new polishing techniques applied to a variety of substrates. This study benefits from previous studies of large missions carried out over the past two decades and, in most areas, points to mission requirements no more stringent than those of Chandra.
We present the characterization of a new event-driven X-ray hybrid CMOS detector developed by Penn State University in collaboration with Teledyne Imaging Sensors. Along with its low susceptibility to radiation damage, low power consumption, and fast readout time to avoid pile-up, the Speedster-EXD has been designed with the capability to limit its readout to only those pixels containing charge, thus enabling even faster effective frame rates. The threshold for the comparator in each pixel can be set by the user so that only pixels with signal above the set threshold are read out. The Speedster-EXD hybrid CMOS detector also has two new in-pixel features that reduce noise from known noise sources: (1) a low-noise, high-gain CTIA amplifier to eliminate crosstalk from interpixel capacitance (IPC) and (2) in-pixel CDS subtraction to reduce kTC noise. We present the read noise, dark current, IPC, energy resolution, and gain variation measurements of one Speedster-EXD detector.
We present preliminary characterization of the Speedster-EXD, a new event driven hybrid CMOS detector (HCD) developed in collaboration with Penn State University and Teledyne Imaging Systems. HCDs have advantages over CCDs including lower susceptibility to radiation damage, lower power consumption, and faster read-out time to avoid pile-up. They are deeply depleted and able to detect x-rays down to approximately 0.1 keV. The Speedster-EXD has additional in-pixel features compared to previously published HCDs including: (1) an in-pixel comparator that enables read out of only the pixels with signal from an x-ray event, (2) four different gain modes to optimize either full well capacity or energy resolution, (3) in-pixel CDS subtraction to reduce read noise, and (4) a low-noise, high-gain CTIA amplifier to eliminate interpixel capacitance crosstalk. When using the comparator feature, the user can set a comparator threshold and only pixels above the threshold will be read out. This feature can be run in two modes including single pixel readout in which only pixels above the threshold are read out and 3x3 readout where a 3×3 region centered on the central pixel of the X-ray event is read out. The comparator feature of the Speedster-EXD increases the detector array effective frame rate by orders of magnitude. The new features of the Speedster-EXD hybrid CMOS x-ray detector are particularly relevant to future high throughput x-ray missions requiring large-format silicon imagers.
Si Hybrid CMOS detectors (HCDs) are sensitive to X-rays between approximately 0.2 – 20 keV. HCDs can provide superior performance to traditional CCDs in multiple areas: faster read out time, windowed read out mode, less susceptible to radiation & micrometeoroid damage, and lower power consumption. X-ray detectors designed for use in astronomical observatories must have an optical blocking filter to prevent the detectors from being saturated by optical light. We have previously reported on the successful deposition of an Al optical blocking layer directly onto the surface of HCDs. These blocking filters were deposited with multiple thicknesses from 180 – 1000 Å and successfully block optical light at all thicknesses, with minimal impact expected on quantum efficiency at the energies of interest for these detectors. The thin Al layer is not expected to impact quantum efficiency at the energies of interest for these detectors. We report energy dependent soft X-ray quantum efficiency measurements for multiple HCDs with different optical blocking filter thicknesses.
We report on the characterization of four HAWAII Hybrid Si CMOS detectors (HCD) developed for use as X-ray
detectors as part of a joint program between Penn State University and Teledyne Imaging Sensors (TIS).
Interpixel capacitive crosstalk (IPC) has been measured for standard H1RG detectors as well as a specially
developed H2RG that uses a unique bonding structure. The H2RG shows significant reduction in IPC, as reported
by Griffith et al. 2012. Energy resolution at 1.5 & 5.9 keV was measured as well as read noise for each detector.
Dark current as a function of temperature is reported from 150 – 210 K and dark current figures of merit are
estimated for each detector. We also discuss upcoming projects including testing of a new HCD called the
Speedster-EXD. This prototype detector will have a low noise, high gain CTIA to reduce IPC and read noise as
well as in-pixel CDS and event flagging. In the coming year PSU and TIS will begin work on a project to
incorporate CTIA and CDS circuitry into the ROIC of a HAWAII HCD like detector to satisfy the small pixel and
high rate needs of future X-ray observatories.
We present the results of x-ray measurements on a hybrid CMOS detector that uses a H2RG ROIC and a unique
bonding structure. The silicon absorber array has a 36μm pixel size, and the readout array has a pitch of 18μm;
but only one readout circuit line is bonded to each 36x36μm absorber pixel. This unique bonding structure gives
the readout an effective pitch of 36μm. We find the increased pitch between readout bonds significantly reduces
the interpixel capacitance of the CMOS detector reported by Bongiorno et al. 20101 and Kenter et al. 2005.2
Future space-based X-ray telescope missions are likely to have significantly increased demands on detector read out
rates due to increased collection area, and there will be a desire to minimize radiation damage in the interests of
maintaining spectral resolution. While CCDs have met the requirements of past missions, active pixel sensors are likely
to be a standard choice for some future missions due to their inherent radiation hardness and fast, flexible read-out
architecture. One form of active pixel sensor is the hybrid CMOS sensor. In a joint program of Penn State University
and Teledyne Imaging Sensors, hybrid CMOS sensors have been developed for use as X-ray detectors. Results of this
development effort and tests of fabricated detectors will be presented, along with potential applications for future
Gamma-ray bursts (GRBs) provide extremely luminous background light sources that can be used to study the
high redshift universe out to z ~ 12. Identification of high-z GRBs has been difficult to date because no good
high-z indicators have been found in the prompt or afterglow emission of GRBs, so ground-based spectroscopic
observations are required. JANUS is an Explorer mission that incorporates a GRB locator and a near-IR
telescope with low resolution spectroscopic capability so that it can measure the redshifts of GRBs immediately
after their discovery. It is expected to discover 50 GRBs with z > 5 as well as hundreds of high redshift quasars.
JANUS will facilitate study of the reionization phase, star formation, and galaxy formation in the very early
universe. Here we discuss the mission design and status.
The JANUS mission concept is designed to study the high redshift universe using a small, agile Explorer class
observatory. The primary science goals of JANUS are to use high redshift (6<z<12) gamma ray bursts and quasars to
explore the formation history of the first stars in the early universe and to study contributions to reionization. The X-Ray
Coded Aperture Telescope (XCAT) and the Near-IR Telescope (NIRT) are the two primary instruments on JANUS.
XCAT has been designed to detect bright X-ray flashes (XRFs) and gamma ray bursts (GRBs) in the 1-20 keV energy
band over a wide field of view (4 steradians), thus facilitating the detection of z>6 XRFs/GRBs, which can be further
studied by other instruments. XCAT would use a coded mask aperture design with hybrid CMOS Si detectors. It would
be sensitive to XRFs and GRBs with flux in excess of approximately 240 mCrab. In order to obtain redshift
measurements and accurate positions from the NIRT, the spacecraft is designed to rapidly slew to source positions
following a GRB trigger from XCAT. XCAT instrument design parameters and science goals are presented in this paper.
The recent development of active pixel sensors as X-Ray focal plane arrays will place them in contention with
CCDs on future satellite missions. Penn State University (PSU) is working with Teledyne Imaging Sensors
(TIS) to develop X-Ray Hybrid CMOS devices (HCDs), a type of active pixel sensor with fast frame rates,
adaptable readout timing and geometry, low power consumption, and inherent radiation hardness. CCDs have
been used with great success on the current generation of X-Ray telescopes (e.g. Chandra, XMM, Suzaku, and
Swift). However, their bucket-brigade readout architecture, which transfers charge across the chip with discrete
component readout electronics, results in clockrate limited readout speeds that cause pileup (saturation) of bright
sources and an inherent susceptibility to radiation induced displacement damage that limits mission lifetime. In
contrast, HCDs read pixels through the detector substrate with low power, on-chip readout integrated circuits.
Faster frame rates, achieved with adaptable readout timing and geometry, will allow the next generation's larger
effective area telescopes to observe brighter sources free of pileup. In HCDs, radiation damaged lattice sites
affect a single pixel instead of an entire row. The PSU X-ray group is currently testing 4 Teledyne HCDs,
with low cross-talk CTIA devices in development. We will report laboratory measurements of HCD readnoise,
interpixel-capacitance and its impact on event selection, linearity, and energy resolution as a function of energy.
JANUS is a NASA small explorer class mission which just completed phase A and was intended for a 2013 launch date.
The primary science goals of JANUS are to use high redshift (6<z<12) gamma ray bursts and quasars to explore the
formation history of the first stars in the early universe and to study contributions to reionization. The X-Ray Flash
Monitor (XRFM) and the Near-IR Telescope (NIRT) are the two primary instruments on JANUS. XRFM has been
designed to detect bright X-ray flashes (XRFs) and gamma ray bursts (GRBs) in the 1-20 keV energy band over a wide
field of view (4 steradians), thus facilitating the detection of z>6 XRFs/GRBs, which can be further studied by other
instruments. XRFM would use a coded mask aperture design with hybrid CMOS Si detectors. It would be sensitive to
XRFs/GRBs with flux in excess of approximately 240 mCrab. The spacecraft is designed to rapidly slew to source
positions following a GRB trigger from XRFM. XRFM instrument design parameters and science goals are presented in
The development of Hybrid CMOS Detectors (HCDs) for X-Ray telescope focal planes will place them in contention
with CCDs on future satellite missions due to their faster frame rates, flexible readout scenarios, lower
power consumption, and inherent radiation hardness. CCDs have been used with great success on the current
generation of X-Ray telescopes (e.g. Chandra, XMM, Suzaku, and Swift). However their bucket-brigade readout
architecture, which transfers charge across the chip with discrete component readout electronics, results in
clockrate limited readout speeds that cause pileup (saturation) of bright sources and an inherent susceptibility
to radiation induced displacement damage that limits mission lifetime. In contrast, HCDs read pixels with low
power, on-chip multiplexer electronics in a random access fashion. Faster frame rates achieved with multi-output
readout design will allow the next generation's larger effective area telescopes to observe bright sources free of
pileup. Radiation damaged lattice sites effect a single pixel instead of an entire row. Random access, multi-output
readout will allow for novel readout modes such as simultaneous bright-source-fast/whole-chip-slow readout. In
order for HCDs to be useful as X-Ray detectors, they must show noise and energy resolution performance similar
to CCDs while retaining advantages inherent to HCDs. We will report on readnoise, conversion gain, and energy
resolution measurements of an X-Ray enhanced Teledyne HAWAII-1RG (H1RG) HCD and describe techniques
of H1RG data reduction.
In a joint program of Penn State University and Teledyne Imaging Sensors, hybrid CMOS sensors have been developed
for use as X-ray detectors. This detector technology can provide major improvements in performance relative to CCDs,
which are the current standard technology used in the focal planes of X-ray telescopes (e.g. Chandra, XMM, Suzaku, and
Swift). Future X-ray telescope missions are all likely to have significantly increased collection area. If standard CCDs
are used, the effects of saturation (pile-up) will have a major impact, while radiation damage will impact the quality and
lifetime of the detectors. By reading out the hybrid CMOS detector in a pixel-by-pixel fashion at high speeds, with an
energy resolution similar to CCDs, CMOS sensors could increase the range of pile-up free operation by several orders of
magnitude. They are also several orders of magnitude more radiation hard than typical CCDs since they transfer charge
through the thickness of the device, rather than across the length of its surface. Furthermore, hybrid CMOS detectors
can be programmed to read out any variety of windowed regions, which leads to versatility and speed. All of this can be
achieved, in principle, while maintaining the same quantum efficiencies achievable in CCDs. Results of this
development effort and preliminary tests of fabricated detectors will be presented, along with potential applications for
future missions such as EDGE and Constellation-X.
The X-ray telescope (XRT) on board the Swift Gamma Ray Burst Explorer has successfully operated since the spacecraft
launch on 20 November 2004, automatically locating GRB afterglows, measuring their spectra and lightcurves and
performing observations of high-energy sources. In this work we investigate the properties of the instrumental
background, focusing on its dynamic behavior on both long and short timescales. The operational temperature of the
CCD is the main factor that influences the XRT background level. After the failure of the Swift active on-board
temperature control system, the XRT detector now operates at a temperature range between -75C and -45C thanks to a
passive cooling Heat Rejection System. We report on the long-term effects on the background caused by radiation,
consisting mainly of proton irradiation in Swift's low Earth orbit and on the short-term effects of transits through the
South Atlantic Anomaly (SAA), which expose the detector to periods of intense proton flux. We have determined the
fraction of the detector background that is due to the internal, instrumental background and the part that is due to
unresolved astrophysical sources (the cosmic X-ray background) by investigating the degree of vignetting of the
measured background and comparing it to the expected value from calibration data.