MEASUREMENT OF THE RADIUS OF NEUTRON STARS WITH HIGH SIGNAL-TO-NOISE QUIESCENT LOW-MASS X-RAY BINARIES IN GLOBULAR CLUSTERS

By S. Guillot, Mathieu Servillat, N. Webb, R. Rutledge. 2012

189 citations recorded by the source corpus.

This paper presents the measurement of the neutron star (NS) radius using the thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular clusters (GCs). Recent observations of NSs have presented evidence that cold ultra dense matter—present in the core of NSs—is best described by “normal matter” equations of state (EoSs). Such EoSs predict that the radii of NSs, RNS, are quasi-constant (within measurement errors, of ∼10%) for astrophysically relevant masses (MNS>0.5 M☉). The present work adopts this theoretical prediction as an assumption, and uses it to constrain a single RNS value from five qLMXB targets with available high signal-to-noise X-ray spectroscopic data. Employing a Markov chain Monte-Carlo approach, we produce the marginalized posterior distribution for RNS, constrained to be the same value for all five NSs in the sample. An effort was made to include all quantifiable sources of uncertainty into the uncertainty of the quoted radius measurement. These include the uncertainties in the distances to the GCs, the uncertainties due to the Galactic absorption in the direction of the GCs, and the possibility of a hard power-law spectral component for count excesses at high photon energy, which are observed in some qLMXBs in the Galactic plane. Using conservative assumptions, we found that the radius, common to the five qLMXBs and constant for a wide range of masses, lies in the low range of possible NS radii, (90%-confidence). Such a value is consistent with low-RNS equations of state. We compare this result with previous radius measurements of NSs from various analyses of different types of systems. In addition, we compare the spectral analyses of individual qLMXBs to previous works.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/06a41dd0d681c64b720fdf305c7c106b82a85977

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In Astronomy and Astrophysics

1. J. Lattimer
2. A. Steiner
3. S. Guillot
4. M. Hempel
5. C. Heinke
6. F. Özel
7. T. Güver
8. Emanuele Berti

Citations in the corpus

• Constraining the mass and radius of neutron stars in globular clusters (2017, methodology): “Guillot et al. (2013) and Özel et al. (2016) have found smaller radii by assuming that (all or most) QLMXB atmospheres must be composed of H. Özel et al. (2016) also use data from photospheric expansion Xray bursts, but their small radii were strongly driven by the QLMXB data.”
• Symmetry energy impact in simulations of core-collapse supernovae (2013, background): “e compatible with the current maximum neutron-star mass constraint of 2:01 0:04 M. The determination of NS radii is still a very challenging task. Several groups obtain substantially dierent results[23,59,60,61,62] due to distinct model assumptions, e.g. composition and properties of the atmosphere.”
• EQUATION OF STATE AND NEUTRON STAR PROPERTIES CONSTRAINED BY NUCLEAR PHYSICS AND OBSERVATION (2013, result): “A recent analysis (Guillot et al. 2013) of five quiescent neutron stars in low-mass X-ray binaries in globular clusters, in which it was assumed that the stars all had the same radius, determined the radius to be R = 9.1+1.3−1.5 km to 90% confidence, which is marginally consistent with our results.”
• Constraints on the symmetry energy using the mass-radius relation of neutron stars (2014, unknown): “Inferred properties of QLMXBs Source D (kpc) NH21 R∞ (km) z NH21 R∞ (km) z Guillot et al. (2013) Lattimer & Steiner (2013) M28 5.5± 0.3 2.52 12.84+1.50−1.48 0.198 +0.485 −0.120 1.89 10.65 +1.27 −1.14 0.212 +0.456 −0.123 NGC 6397 2.02± 0.18 0.96 8.42+1.32−1.36 0.242 +0.278 −0.106 1.4 11.66 +1.94…”
• CONSTRAINING THE SYMMETRY PARAMETERS OF THE NUCLEAR INTERACTION (2012, background): “A recent study found radii ranging from 8 km to 23 km (Guillot et al. 2013), using a low magnetic field, pure hydrogen atmosphere.”
• Evidence for a maximum mass cut-off in the neutron star mass distribution and constraints on the equation of state (2017, background): “Measurements of NS masses and radii together can put strong constraints on the EoS (Read et al. 2009; Özel & Psaltis 2009; Özel et al. 2010; Steiner et al. 2010; Guillot et al. 2013; Steiner et al. 2013a,b; Özel et al. 2016).”
• THE DENSE MATTER EQUATION OF STATE FROM NEUTRON STAR RADIUS AND MASS MEASUREMENTS (2015, methodology): “These observations include those summarized in Table 1 of Guillot et al. (2013) as well as the Chandra observations of the qLMXB in M30 (ObsID 2679; Lugger et al. 2007) and of the qLMXB in ω Cen (ObsIDs 13726 and 13727), as described in Guillot & Rutledge (2014).”
• Neutron star mass and radius measurements from atmospheric model fits to X-ray burst cooling tail spectra (2017, methodology): “To explore the parameter spaces we implement an affine-invariant ensemble sampler as discussed in Goodman & Weare 2010 (see also Guillot et al. 2013).”