X-ray Bursts and Oscillations: Prospects with NICER
Abstract
X-ray bursts (Type I) are produced by thermonuclear flashes in the accreted surface layers of some neutron stars in Low Mass X-ray Binaries (LMXBs). High frequency oscillations are observed during some of these bursts. These "burst oscillations" result from rotational modulation of an inhomogeneous temperature distribution on the neutron star surface induced by ignition and subsequent spreading of the thermonuclear flash. They provide a means to measure the spin rates of accreting neutron stars and since the burst emission arises from the neutron star surface, a unique probe of neutron star structure. To date, virtually all observations of such oscillations have been made with NASA's Rossi X-ray Timing Explorer (RXTE). We have developed a burst model employing the Schwarzschild + Doppler approximation for surface emission coupled with realistic flame spreading geometries and burst cooling to compute light curves and oscillation amplitudes for both the rising and cooling phases of X-ray bursts. We use this model to explore the capabilities for the Neutron star Interior Composition ExploreR (NICER) to detect and study burst oscillations, particularly in the energy band below 3 keV. NICER is an International Space Station attached payload (X-ray telescope) with capabilities optimized for fast timing of neutron stars in the 0.2-10 keV band. It has large collecting area (twice that of the XMM-Newton EPIC-pn camera), CCD-quality spectral resolution, and high-precision time tagging referenced to UTC through an onboard GPS receiver. NICER will begin its 18-month prime mission around the end of 2016. We will present results of simulated X-ray bursts with NICER that explore its burst oscillation detection capabilities and prospects for inferring neutron star properties from phase-resolved spectra.
- Publication:
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AAS/High Energy Astrophysics Division #15
- Pub Date:
- April 2016
- Bibcode:
- 2016HEAD...1512023S