Mission Overview

Astrophysics on the International Space Station -
Understanding ultra-dense matter through soft X-ray timing

  • Science: A proposed International Space Station (ISS) payload dedicated to the study of neutron stars. A fundamental investigation of extremes in gravity, material density, and electromagnetic fields

  • Launch: October 2016, SpaceX-12

  • Duration: 18 (minimum 12) months, with an optional Guest Observer program

  • Platform: ISS ExPRESS Logistics Carrier (ELC), with active pointing over 2π steradians

  • Instrument: X-ray (0.2-12 keV) "concentrator" optics and silicon-drift detectors. GPS position and absolute time reference to better than 300 ns.

NICER on ISS Effective area curve


ISS Accommodations

As established platform and a benign environment

tracking

The ISS offers:

  • Established infrastructure (transport, power, comm, etc.) that reduces risk
  • Generous resources that simplify design and reduce cost.
  • A stable platform for arcminute astronomy

NICER's design:

  • Is tolerant of ISS vibrations
  • Is insensitive to the ISS contamination and radiation environments, with safe-stow capability
  • Provides high (> 65%) observing efficiency.



Science Objectives

Neutron Stars - Unique environments in which all four
fundamental forces of Nature are simultaneously important

pulsar
  • To address NASA and National Academy of Sciences strategic questions
  • To resolve the nature of ultradense matter at the threshold of collapse to a black hole
  • To reveal interior composition, dynamic processes, and radiation mechanisms of neutron stars.

ObjectiveMeasurements
Structure - Reveal the nature of matter in the interiors of neutron stars Neutron star radii to +5%. Cooling timescales
Dynamics - Reveal the nature of matter in the interiors of neutron stars Stability of pulsars as clocks. Properties of outbursts, oscillations, and precession
Energetics - Determine how energy is extracted from neutron stars. Intrinsic radiation patterns, spectra, and luminosities.
Diagram of a neutron star
Neutron Star and Strange Quark Star


Science Measurements

Reveal stellar structure through lightcurve modeling, long-term timing, and pulsation searches

Thermal Lightcurve Model
Lightcurve modeling constrains the compactness (M/R) and viewing geometry of a non-accreting millisecond pulsar through the depth of modulation and harmonic content of emission from rotating hot-spots, thanks to gravitational light-bending...
Energy vs. Pulse Phase
... while phase-resolved spectroscopy promises a direct constraint on radius R.
Counts vs. Pulse Phase

Simulations demonstrate how well an assumed neutron star radius can be recovered. The +5% (3σ) measurement goal is attained in less than 1 Msec.

The resulting allowed regions in the M-R plane rule out proposed families of neutron star equations of state. The best mass measurements alone can't distinguish among competing models.

Graphs showing number of photons and Solar Mass versus Neutron Star Radius


Neutron Star Science Synergies

Interplay between multiwavelength capabilities amplifies scientific returns from all

Diagram showing interplay between NICER, Fermi, Future X-ray polarimeter, Radio, MAXI, and other all-sky monitors


Proposed Guest Investigator/Guest Observer Program

X-ray astrophysics beyond neutron stars, continuity of RXTE timing science

A proposed two-part Guest Investigator/Observer program, modeled after Swift:

  • In Year 1, support for corollary neutron star research: theory & complementary multiwavelength observations
  • In Year 2, solicitation of proposals for new observations with NICER, not necessarily targeting neutron stars.

NICER baseline and SEO support

Sample science enabled by the NICER GO program

Black holes of all sizes are probed through soft continuum spectroscopy to constrain spins in stellar-mass binaries, power spectra of QPOs to definitely establish ultraluminous X-ray sources as intermediate-mass black holes, and relativistic reflection lines to discriminate among AGN models.

Power vs Frequency
Redshifted Fe Lines

Redshifted Fe lines from galaxy clusters reveal star-formation history and poorly understood feedback processes that drive galaxy evolution. (Left) A z = 1.18 line is seen well above the diffuse X-ray back-ground (blue).


Plus...

  • Temporal and spectral variability studies of bright coronal stars can be conducted on much shorter timescales than previously possible
  • The interplay of accretion processes and gravitational radiation in double-degenerate systems can be studied through QPOs in "polars" and long-term timing of SN Ia progenitors
  • Emission lines and soft excesses in high-mass X-ray binaries probe field strengths, accretion geometry, and long-term spin evolution.