http://arxiv.org/abs/1610.08770
We study the crust effects on fast-rotating configurations of neutron stars (NSs). For this aim, we employ four unified equations of state (EoS) for both the cores and crusts, namely BCPM, BSk20, BSk21, Shen-TM1, as well as two non-unified EoS widely used in the literature, i.e. APR and GM1 EoS. All the core EoSs satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We show that the NS mass-equatorial radius relations are slightly affected by the smoothness at the core-crust matching interface. However, the uncertainties in the crust EoS and the matching interface bring insignificant changes, even at maximally rotating (Keplerian) configurations. For all four unified EoS, rotations can increase the star’s gravitational mass up to $18\%-19\%$ and the equatorial radius by $29\%-36\%$. For stars as heavy as 1.4 M$_{\odot}$, the radius increase is more pronounced, reaching $41\%-43\%$, i.e. 5 – 6 km. Moreover, by comparing the present calculations with recent simultaneous determinations of mass and radius for two X-ray bursts, 4U 1608-52 and 4U 1724-307, we propose that they might be rapidly spinning NSs, in order to account for their measured large radii.
A. Li, N. Zhang, B. Qi, et. al.
Fri, 28 Oct 16
32/73
Comments: 10 pages, 4 figures, 3 tables
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