Abstract
Context. Pulsating thermal X-ray emission from millisecond pulsars can be used to obtain constraints on the neutron star equation of state, but to date only five such sources have been identified. Of these five millisecond pulsars, only two have well-constrained neutron star masses, which improve the determination of the radius via modelling of the X-ray waveform. Aims. We aim to find other millisecond pulsars that already have well-constrained mass and distance measurements that show pulsed thermal X-ray emission in order to obtain tight constraints on the neutron star equation of state. Methods. The millisecond pulsar PSR J1909–3744 has an accurately determined mass, M = 1.54 ± 0.03 M⊙ (1σ error) and distance, D = 1.07 ± 0.04 kpc. We analysed XMM-Newton data of this 2.95 ms pulsar to identify the nature of the X-ray emission. Results. We show that the X-ray emission from PSR J1909–3744 appears to be dominated by thermal emission from the polar cap. Only a single component model is required to fit the data. The black-body temperature of this emission is $ {kT}=0.26^{0.03}_{0.02} $ keV and we find a 0.2–10 keV un-absorbed flux of 1.1 × 10−14 erg cm−2 s−1 or an un-absorbed luminosity of 1.5 × 1030 erg s−1. Conclusion. Thanks to the previously determined mass and distance constraints of the neutron star PSR J1909–3744, and its predominantly thermal emission, deep observations of this object with future X-ray facilities should provide useful constraints on the neutron star equation of state.
Highlights
Fifty years after the discovery of neutron stars, the nature of the material making up their core remains largely unknown
In this paper we investigate the nature of the X-ray emission with an aim to constraining the neutron star equation of state
PSR J1909–3744 was significantly detected with all three cameras, with 140 ± 12, 33 ± 6, and 38 ± 6 background subtracted counts detected with the pn, the MOS 1, and the MOS 2 respectively, see Table 1
Summary
Fifty years after the discovery of neutron stars, the nature of the material making up their core remains largely unknown. A promising way of inferring radii (and masses) is through modelling the X-ray waveform of a neutron star with a fairly low magnetic field and which shows predominantly thermal X-ray emission from its polar caps. This provides a measure of the mass and radius of the star (e.g., Pavlov & Zavlin 1997; Bogdanov et al 2007; Leahy et al 2011). Five millisecond pulsars have been shown to have predominantly thermal X-ray emission and show X-ray pulsations These are PSR J0030+0451, PSR J2124–3358, PSR J0437– 4715, PSR J1024–0719 and PSR 1614–2230 (e.g., Zavlin 2006; Bogdanov et al 2008; Bogdanov 2013; Pancrazi et al 2012). For example Bogdanov & Grindlay (2009) found a lower limit R > 10.4 km (at 99.9% confidence) when
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
