Rejecting proposed dense-matter equations of state with quiescent low-mass X-ray binaries
Sep 15, 20148 pages
Published in:
- Astrophys.J.Lett. 796 (2014) 1, L3
- Published: Oct 31, 2014
e-Print:
- 1409.4306 [astro-ph.HE]
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Abstract: (IOP)
Neutrons stars are unique laboratories for discriminating between the various proposed equations of state of matter at and above nuclear density. One sub-class of neutron stars—those inside quiescent low-mass X-ray binaries (qLMXBs)—produce a thermal surface emission from which the neutron star radius (R (NS)) can be measured, using the widely accepted observational scenario for qLMXBs, assuming unmagnetized H atmospheres. In a combined spectral analysis, this work first reproduces a previously published measurement of the R (NS), assumed to be the same for all neutron stars, using a slightly expanded data set. The radius measured is . On the basis of spectral analysis alone, this measured value is not affected by imposing an assumption of causality in the core. However, the assumptions underlying this R (NS) measurement would be falsified by the observation of any neutron star with a mass >2.6 M (☉), since radii would be rejected if causality is assumed, which would exclude most of the R (NS) parameter space obtained in this analysis. Finally, this work directly tests a selection of dense matter equations of state: WFF1, AP4, MPA1, PAL1, MS0, and three versions of equations of state produced through chiral effective theory. Two of those, MS0 and PAL1, are rejected at the 99% confidence level, accounting for all quantifiable uncertainties, while the other cannot be excluded at >99% certainty.Note:
- 10 pages, 3 figures, 2 tables. Accepted in ApJL. New figures added!
- X-rays: binaries
- stars: neutron
- equation of state
- dense matter
References(58)
Figures(3)