The Neutron star Interior Composition ExploreR Mission
The Neutron star Interior Composition Explorer (NICER) is an International
Space Station (ISS) payload devoted to the study of neutron stars through soft
X-ray timing. Neutron stars are unique environments in which all four
fundamental forces of nature are simultaneously important. They squeeze more
than 1.4 solar masses into a city-size volume, giving rise to the highest
stable densities known anywhere. The nature of matter under these conditions
is a decades-old unsolved problem, one most directly addressed with
measurements of the masses and, especially, radii of neutron stars to high
precision (i.e., better than 10 percent uncertainty). With few such
constraints forthcoming from observations, theory has advanced a host of
models to describe the physics governing neutron star interiors; these models
can be tested with astrophysical observations.
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. The NICER mission achieves these goals by
deploying an X-ray timing and spectroscopy instrument on the International
Space Station (ISS).
By answering a long-standing astrophysics question - How big is a neutron
star? - NICER will confront nuclear physics theory with unique measurements,
exploring the exotic states of matter within neutron stars through
rotation-resolved X-ray spectroscopy. The capabilities that NICER brings to
this investigation are unique: simultaneous fast timing and spectroscopy, with
low background and high throughput. NICER will also provide continuity in
X-ray-timing astrophysics more broadly, post-Rossi X-ray Timing Explorer,
through a Guest Observer program. Finally, in addition to its science goals,
NICER will enable the first space demonstration of pulsar-based navigation of
spacecraft, through the Station Explorer for X-ray Timing and Navigation
Technology (SEXTANT) enhancement to the mission, funded by the NASA Space
Technology Mission Directorate's Game-Changing Development program.
NICER's X-ray Timing Instrument (XTI) represents an innovative configuration
of high-heritage components. The heart of the instrument is an aligned
collection of 56 X-ray "concentrator" optics (XRC) and silicon drift detector
(SDD) pairs. Each XRC collects X-rays over a large geometric area from a
roughly 30 arcmin2 region of the sky and focuses them onto a small
SDD. The SDD
detects individual photons, recording their energies with good (few percent)
spectral resolution and their detection times to an unprecedented 100
nanoseconds RMS relative to Universal Time. Together, this assemblage provides
a high signal-to-noise-ratio photon-counting capability within the 0.2-12 keV
X-ray band, perfectly matched to the typical spectra of neutron stars as well
as a broad collection of other astrophysical sources.
From NICER's ISS platform, a star-tracker-based pointing system allows the
XTI to point to and track celestial targets over nearly a full hemisphere.
The pointing system design accommodates the ISS vibration and contamination
environments, and enables (together with NICER's GPS-based absolute timing)
high-precision pulsar light-curve measurements through ultra-deep exposures
spanning the 18-month mission lifetime. Anticipated launch of NICER is in
Simulated NICER count rates and spectra can be derived using the WebPIMMS and WebSPEC tools.
A 12-slide overview of NICER science is available here.
More NICER documentation and publications.
If you would like to receive email about NICER developments, please subscribe to the NICER-announce email list.
For those interested in general astronomy/astrophysics information please go to the Education and Public Outreach site.