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 Observations of the 2020 X-ray Minimum of eta Carinae (24 Feb 2020)
    NICER has observed the 2020 X-ray minimum of eta Carinae, a long-period eccentric binary system which produces X-ray emission from the collision of the powerful stellar winds from the two stars. X-ray monitoring observations with NICER showed that the X-ray minimum began on 2020-02-13, at which time the observed X-ray flux dropped by about two orders of magnitude from the peak flux seem about 1 month earlier. The NICER observations help establish variations in the stellar wind mass loss and provide a probe of the dense inner wind of the Luminous Blue Variable primary star.
  • Re-brightening and decaying of MAXI J1348-630 as observed with NICER (11 Feb 2020)
    NICER observations of a new black hole candidate MAXI J1348-630 from Feb. 7 to 10 showed the source declining in X-ray flux by about a factor of 2 during this interval. NICER spectra show that the source is currently in the hard state. NICER will continue monitoring the source about once per day until the outburst fades.
  • Initial NICER observations of the mysterious source Swift J0840.7-3516 (aka GRB 200205A) and detection of short X-ray flaring activity (07 Feb 2020)
    The source Swift J0840.7-3516 was originally reported as a Gamma-ray burst sourcce by the Swift BAT on February 5. Followup observations by the Swift XRT showed X-ray emission that was inconsistent with a GRB, along with the possible detection of an 8.96 seconds. Followup X-ray observations with NICER showed X-ray flaring during which the X-ray flux increasd by a factor of 4, but did not confirm the X-ray period.
  • NICER observes a new outburst of V4641 Sgr (04 Feb 2020)
    V4641 Sgr is a binary system that contains a 6.4 solar mass black hole which went into X-ray outburst in early January. Observations by NICER on January 31 provided the best measure of the 2-10 keV spectrum and showed an inner disk radius temperature of about 1.5 keV, with no visible features in the power spectrum in the short NICER observation.
  • NICER sees a state change in MAXI J0637-430 (30 Jan 2020)
    NICER observations of the newly-discovered X-ray transient MAXI J0637-430 indicate that the source is a black hole X-ray binary system. Recent observations detail the decline of the soft, thermal X-ray emission from the source which entered a hard state on January 14, 2020, indicating a signficant change in the accretion disk around the black hole.

[More NICER News]