Publication Date:
2016-10-08
Description:
We present a hard X-ray Nuclear Spectroscopic Telescope Array ( NuSTAR ) observation of PSR J0437–4715, the nearest millisecond pulsar. The known pulsations at the apparent pulse period ${\sim }5.76{\,{\rm ms}}$ are observed with a significance of 3.7, at energies up to 20 keV above which the NuSTAR background dominates. We measure a photon index = 1.50 ± 0.25 (90 per cent confidence) for the power-law fit to the non-thermal emission. It had been shown that spectral models with two or three thermal components fit the XMM–Newton spectrum of PSR J0437–4715, depending on the slope of the power-law component, and the amount of absorption of soft X-rays. The new constraint on the high-energy emission provided by NuSTAR removes ambiguities regarding the thermal components of the emission below $3{\,{\rm keV}}$ . We performed a simultaneous spectral analysis of the XMM–Newton and NuSTAR data to confirm that three thermal components and a power law are required to fit the 0.3–20 keV emission of PSR J0437–4715. Adding a ROSAT -PSPC spectrum further confirmed this result and allowed us to better constrain the temperatures of the three thermal components. A phase-resolved analysis of the NuSTAR data revealed no significant change in the photon index of the high-energy emission. This NuSTAR observation provides further impetus for future observations with the NICER mission ( Neutron Star Interior Composition Explorer ) whose sensitivity will provide much stricter constraints on the equation of state of nuclear matter by combining model fits to the pulsar's phase-folded light curve with the pulsar's well-defined mass and distance from radio timing observations.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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