NICER / ISS Science Nugget for September 6, 2018

MSP timing stability rivals ground-based radio telescopes

One of NICER's major science objectives it to determine the long time timing stability of the pulses from millisecond pulsars. Some millisecond pulsars, such as PSR B1937+21, produce pulses so regularly spaced that they tick with stabilities that rival atomic clocks. For the first time, NICER will provide a measure of the long term stability of a handful of millisecond pulsars in the X-ray band.

NICER observations of stability in a quantity called "sigma-Z" is shown in the figure below compared to radio telescope measurements. NICER's X-ray band measurements are immune from the propagation effects that limit radio observations on long time scales. NICER's measurements are on track to rival the most stable radio telescope measurements of pulsar spin stability.

Observations of pulsar timing stability comparing NICER to ground-based radio telescopes
Figure: A measure of timing stability, Sigma-z , vs. the time span over which the data are fitted for the millisecond pulsar PSR B1937+21. Red, black, and blue points show Sigma-z for NICER, Nancay decimetric Radio Telescope (NRT), and NANOGrav (a collection of radio northern hemisphere telescopes) data, respectively. The dashed line shows the slope for the case where timing precision is limited by white noise only. The green line marks the first two years of the NICER mission.

In addition to providing valuable insight into neutron star dynamics, these measurements will help us better evaluate the utility of millisecond pulsars as high precision time standards and navigational beacons for deep space travel.

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