Neutron star Interior Composition ExploreR (NICER) is a NASA instrument to be onboard International Space Station, which is equipped with 56 pairs of an X-ray concentrator (XRC) and a silicon drift detector for high timing observations. The XRC is based on an epoxy replicated thin aluminum foil X-ray mirror, similar to those of Suzaku and ASTRO-H (Hitomi), but only a single stage parabolic grazing incidence optic. Each has a focal length of 1.085m and a diameter of 105 mm, with 24 confocally aligned parabolic shells. Grazing incident angles to individual shells range from 0.4 to 1.4 deg. The flight 56 XRCs have been completed and successfully delivered to the payload integration. All the XRC was characterized at the NASA/GSFC 100-m X-ray beamline using 1.5 keV X-rays (some of them are also at 4.5 keV). The XRC performance, effective area and point spread function, was measured by a CCD camera and a proportional counter. The average effective area is about 44 cm2 at 1.5 keV and about 18 cm2 at 4.5 keV, which is consistent with a micro-roughness of 0.5nm from individual shell reflectivity measurements. The XRC focuses about 91% of X-rays into a 2mm aperture at the focal plane, which is the NICER detector window size. Each XRC weighs only 325 g. These performance met the project requirement. In this paper, we will present summary of the flight XRC performance as well as co-alignment results of the 56 XRCs on the flight payload as it is important to estimate the total effective for astronomical observations.
During 2014 and 2015, NASA's Neutron star Interior Composition Explorer (NICER) mission proceeded success- fully through Phase C, Design and Development. An X-ray (0.2-12 keV) astrophysics payload destined for the International Space Station, NICER is manifested for launch in early 2017 on the Commercial Resupply Services SpaceX-11 flight. Its scientific objectives are to investigate the internal structure, dynamics, and energetics of neutron stars, the densest objects in the universe. During Phase C, flight components including optics, detectors, the optical bench, pointing actuators, electronics, and others were subjected to environmental testing and integrated to form the flight payload. A custom-built facility was used to co-align and integrate the X-ray "con- centrator" optics and silicon-drift detectors. Ground calibration provided robust performance measures of the optical (at NASA's Goddard Space Flight Center) and detector (at the Massachusetts Institute of Technology) subsystems, while comprehensive functional tests prior to payload-level environmental testing met all instrument performance requirements. We describe here the implementation of NICER's major subsystems, summarize their performance and calibration, and outline the component-level testing that was successfully applied.
The Neutron star Interior Composition ExploreR (NICER) is set to be deployed on the International Space Station (ISS) in early 2017. It will use an array of 56 Silicon Drift Detectors (SDDs) to detect soft X-rays (0.2 - 12 keV) with 100 nanosecond timing resolution. Here we describe the effort to calibrate the detectors in the lab primarily using a Modulated X-ray Source (MXS).
The MXS that was customized for NICER provides more than a dozen emission lines spread over the instrument bandwidth, providing calibration measurements for detector gain and spectral resolution. In addition, the fluorescence source in the MXS was pulsed at high frequency to enable measurement of the delay due to charge collection in the silicon and signal processing in the detector electronics. A second chamber, designed to illuminate detectors with either 55Fe, an optical LED, or neither, provided additional calibration of detector response, optical blocking, and effectiveness of background rejection techniques. The overall ground calibration achieved total operating time that was generally in the range of 500-1500 hours for each of the 56 detectors.
An instrument called Neutron Star Interior Composition ExploreR (NICER) will be placed on-board the Inter- national Space Station in 2017. It is designed to detect soft X-ray emission from compact sources and to provide both spectral and high resolution timing information about the incoming ux. The focal plane is populated with 56 customized Silicon Drift Detectors. The paper describes the detector system architecture, the electronics and presents the results of the laboratory testing of both ight and engineering units, as well as some of the calibration results obtained with synchrotron radiation in the laboratory of PTB at BESSY II.
The NICER1 mission uses a complicated physical system to collect information from objects that are, by x-ray timing science standards, rather faint. To get the most out of the data we will need a rigorous understanding of all instrumental effects. We are in the process of constructing a very fast, high fidelity simulator that will help us to assess instrument performance, support simulation-based data reduction, and improve our estimates of measurement error. We will combine and extend existing optics, detector, and electronics simulations. We will employ the Compute Unified Device Architecture (CUDA2) to parallelize these calculations. The price of suitable CUDA-compatible multi-giga op cores is about $0.20/core, so this approach will be very cost-effective.
Over a 10-month period during 2013 and early 2014, development of the Neutron star Interior Composition Explorer (NICER) mission  proceeded through Phase B, Mission Definition. An external attached payload on the International Space Station (ISS), NICER is scheduled to launch in 2016 for an 18-month baseline mission. Its prime scientific focus is an in-depth investigation of neutron stars—objects that compress up to two Solar masses into a volume the size of a city—accomplished through observations in 0.2–12 keV X-rays, the electromagnetic band into which the stars radiate significant fractions of their thermal, magnetic, and rotational energy stores. Additionally, NICER enables the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) demonstration of spacecraft navigation using pulsars as beacons. During Phase B, substantive refinements were made to the mission-level requirements, concept of operations, and payload and instrument design. Fabrication and testing of engineering-model components improved the fidelity of the anticipated scientific performance of NICER’s X-ray Timing Instrument (XTI), as well as of the payload’s pointing system, which enables tracking of science targets from the ISS platform. We briefly summarize advances in the mission’s formulation that, together with strong programmatic performance in project management, culminated in NICER’s confirmation by NASA into Phase C, Design and Development, in March 2014.
We performed a series of measurements using X-rays to assess the current performance of the Neutron star Interior Composition ExploreR (NICER) X-ray concentrators during the mission's concept study stage. NICER will use 56 grazing-incidence X-ray concentrators in the optical system with each module focusing the incoming photons to co-aligned silicon drift detectors with 2 mm apertures. Successful X-ray timing and navigation studies require optimal signal to noise, thus by optimizing high throughput concentrators with a large collecting area we can minimize the PSF and reduce the detector aperture size, reducing background. The performance measurements were conducted in a 600 meter X-ray beamline which collimated photons from a soft X-ray source to an X-ray CCD which was used as the detector. Several engineering test units were used to perform these studies by measuring the effective area, on and off-axis resolution, and to assess the effects of a vibration test on the module's optical performance. We have shown that the concentrators have made significant progress towards exceeding NICER's final goals.
We have studied timing properties of the Amptek Silcon Drift Detectors (SDD) using pulsed X-ray source
designed at NASA Goddard Space Flight Center. The proposed Neutron Star Interior Composition Explorer
(NICER) mission will use 56 of these detectors as X-ray sensors in an attached payload to the International
Space Station to study time variability of millisecond X-ray pulsars. Using a rastered pinhole we have measured
the delay times for single X-ray photons as a function of the impact position on the detector, as well as signal
rise time as a function of impact position. We find that the interdependence of these parameters allows us to
determine photon position on the detector by measuring the signal rise time, and, improve the accuracy of the
photon arrival time measurement.
The scientific objective of the X-ray Advanced Concepts Testbed (XACT) is to measure the X-ray polarization
properties of the Crab Nebula, the Crab pulsar, and the accreting binary Her X-1. Polarimetry is a powerful tool for
astrophysical investigation that has yet to be exploited in the X-ray band, where it promises unique insights into neutron
stars, black holes, and other extreme-physics environments. With powerful new enabling technologies, XACT will
demonstrate X-ray polarimetry as a practical and flight-ready astronomical technique. Additional technologies that
XACT will bring to flight readiness will also provide new X-ray optics and calibration capabilities for NASA missions
that pursue space-based X-ray spectroscopy, timing, and photometry.
The Neutron star Interior Composition ExploreR (NICER) is a proposed NASA Explorer Mission of Opportunity dedicated to the study of the extraordinary gravitational, electromagnetic, and nuclear-physics environments embodied by neutron stars. NICER will explore the exotic states of matter within neutron stars, where density and pressure are higher than in atomic nuclei, confronting theory with unique observational constraints. NICER will enable rotation-resolved spectroscopy of the thermal and non-thermal emissions of neutron stars in the soft (0.2–12 keV) X-ray band with unprecedented sensitivity, probing interior structure, the origins of dynamic phenomena, and the mechanisms that underlie the most powerful cosmic particle accelerators known. NICER will achieve these goals by deploying, following launch in December 2016, an X-ray timing and spectroscopy instrument as an attached payload aboard the International Space Station (ISS). A robust design compatible with the ISS visibility, vibration, and contamination environments allows NICER to exploit established infrastructure with low risk. Grazing-incidence optics coupled with silicon drift detectors, actively pointed for a full hemisphere of sky coverage, will provide photon-counting spectroscopy and timing registered to GPS time and position, with high throughput and relatively low background. In addition to advancing a vital multi-wavelength approach to neutron star studies through coordination with radio and γ-ray observations, NICER will provide a rapid-response capability for targeting of transients, continuity in X-ray timing astrophysics investigations post-RXTE through a proposed Guest Observer program, and new discovery space in soft X-ray timing science.
NICER will use full shell aluminum foil X-ray mirrors, similar to those that are currently being developed for the
optics to be used for the XACT sounding rocket mission. Similar X-ray optics have been produced at Goddard
Space Flight Center since the late 1970's. The mirror geometry used in the past and on some present missions
consists of concentric quadrant shell mirrors with a conical approximation to the Wolter 1 geometry. For XACT,
we are developing the next generation of these optics. Two innovations introduced in the mirrors are complete
shells with a curve is in the reflectors' profile to produce a sharper focus than a conical approximation. X-ray
imagers, such as those of Suzaku, ASCA, GEMS, and Astro-H require two reflections. Since XACT and NICER
are using the optics as X-ray concentrators rather than full imaging optics, only one set of reflections is necessary.
The largest shell in the NICER concentrator is 10cm diameter. Small diameter optics benefit from the rigidity
of the full shell design. Also, the simplified support hardware reduced mass, which increases the effective area
per unit mass. With 56 optics on NICER, each consisting of 24 full shell mirrors, an effective production process
is needed for efficient manufacture of these mirrors. This production process is based on heritage techniques but
modified for these new mirrors. This paper presents the production process of the innovative full shell optics
and also results of optical and X-ray tests of the integrated optics.
The SXS instrument is the Soft X-ray micro-calorimeter Spectrometer planned for the Japanese ASTRO-H
satellite, scheduled to be launched in 2014. In this paper, the trade off and modelling for the X-ray absorption
and optical blocking filters will be described. The X-ray absorption filter will optimize the efficiency for high
spectral resolution observations for bright sources at higher energies (notably around the Fe-K line at 6.4 KeV),
given the characteristics of the instrument while the optical blocking filter allows X-ray observations of optically
bright sources. For this mission a novel type of on-off-switchable X-ray calibration source, using light sensitive
photo-cathodes, is being developed, which will be used for gain calibration and contamination monitoring. These
sources will be used by both the SXS and SXI (Soft X-ray Imager) instruments and have the capability to be
pulsed at millisecond intervals. Details of these sources will also be discussed.
MASSIM, the Milli-Arc-Second Structure Imager, is a mission that has been proposed for study within the context
of NASA's Astrophysics Strategic Mission Concept Studies program. It uses a set of achromatic diffractive-refractive
Fresnel lenses on an optics spacecraft to focus 5-11 keV X-rays onto detectors on a second spacecraft
flying in formation 1000 km away. It will have a point-source sensitivity comparable with that of the current
generation of major X-ray observatories (Chandra, XMM-Newton) but an angular resolution some three orders of
magnitude better. MASSIM is optimized for the study of jets and other phenomena that occur in the immediate
vicinity of black holes and neutron stars. It can also be used for studying other astrophysical phenomena on the
milli-arc-second scale, such as those involving proto-stars, the surfaces and surroundings of nearby active stars
and interacting winds.
We describe the MASSIM mission concept, scientific objectives and the trade-offs within the X-ray optics
design. The anticipated performance of the mission and possible future developments using the diffractive-refractive
optics approach to imaging at X-ray and gamma-ray energies are discussed.
NASA's Strategic Plan for Space Sciences currently envisions a mission capable of resolving the event horizons of supermassive black holes, with imaging-spectroscopy capabilities at angular resolutions better than 0.1 microarcsecond. To achieve this goal, the Micro-Arcsecond X-ray Imaging Mission (MAXIM), a broadband X-ray interferometer, is currently under study. Ground-based proof-of-concept efforts include experiments to demonstrate the feasibility of X-ray interferometry with simple optics. We describe here recent advances in laboratory testbeds, at the University of Colorado and at NASA's Goddard Space Flight Center, that essentially replicate Young's double-slit experiment at X-ray energies. A typical apparatus employs four flat mirrors arranged in periscope pairs, with each pair illuminated at grazing incidence by a slit. We discuss the salient features of these experiments, technical hurdles such as metrology and line-of-sight issues, the successful detection of fringes at wavelengths as short as the Al Kalpha line at 8.35 Angstroms, and future upgrades of our facilities.