The Neutron star Interior Composition Explorer Mission


Current Activity:


Requesting Targets of Opportunity (ToOs) with NICER

NICER is capable of following up on Targets of Opportunity (ToO) within 4 hours (depending on source visibility). TOO requests should be submitted via the ARK/RPS NICER Target of Opportunity/Director's Discretionary Time Request form.

The NICER team monitors the Gamma-ray Coordination Network (GCN)/Transient Astronomy Network (TAN).

Any questions regarding how to make TOO requests should be sent to the NICER Helpdesk via the HEASARC's Feedback Form.



NICER was launched aboard a SpaceX Falcon 9 rocket on June 3, 2017 at 17:07 EDT (21:07 UTC)

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.

Simulated NICER count rates and spectra can be derived using the WebPIMMS and WebSPEC tools. The Viewing tool can be used to determine the times when a specific sky position is potentially visible to NICER.

More details are availbale in NICER's Mission Guide. 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.

Artist concept of NICER

Latest News
  • NICER detects X-ray pulsations from the rapidly brightening SAX J1808.4-3658 (08 Aug 2019)
    NICER monitoring of the accreting millisecond X-ray pulsar SAX J1808.4-3658 successfully recovered a 401 Hz pulsation after correcting for delays due to the known binary orbit. The time of ascending node derived from the timing solution is 27 seconds earlier than predicted, which indicates that the orbital expansion is proceeding more slowly than expected.
  • NICER detection of QPOs from EXO 1846-031 (01 Aug 2019)
    Following reports of renewed activity from the X-ray transient EXO 1846-031, NICER executed rapid follow-up observations. These observations detected a sharp QPO at 0.26 Hz. The timing and X-ray spectrum suggest that this source is a black hole X-ray binary in the hard state.
  • GSFC X-ray Technology Opens New Frontiers in Space and on Earth (24 Jul 2019)
    The Miniaturized High-Speed Modulated X-ray Source (MXS) has been chosen as NASA's 2019 Government Invention of the Year. MXS was developed by Keith Gendreau (the NICER Project Scientist) and Zaven Arzoumanian (the NICER Deputy Project Scientist) and was used in the ground calibration of NICER. It also can help generate medical images similar to a CT scan for patients on earth and for astronauts in space.
  • Ultra-luminous X-ray pulsar NGC 300 ULX1 experienced unprecedented spin evolution, study finds (31 May 2019)
    NASA's NICER image shows 22 months of X-ray data recorded by the Space Station payload during its nighttime moves between targets.
  • NASA's NICER Shows Entire Sky in X-rays in Stunning Arc Image (31 May 2019)
    NASA's NICER image shows 22 months of X-ray data recorded by the Space Station payload during its nighttime moves between targets.

[More NICER News]