Implications of latest NICER data for the neutron star equation of state
Len Brandes, Wolfram Weise
Abstract
As an update to our previously performed Bayesian inference analyses of the neutron star matter equation-of-state and related quantities, the additional impact of the recently published NICER data of PSR J0437-4751 is examined. Including the mass and radius distributions of this pulsar in our database results in modest shifts from previously inferred median posterior values of radii <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>R</a:mi> </a:math> and central densities <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:msub> <c:mi>n</c:mi> <c:mi>c</c:mi> </c:msub> </c:math> for representative <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mn>1.4</e:mn> <e:msub> <e:mi>M</e:mi> <e:mo stretchy="false">⊙</e:mo> </e:msub> </e:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"> <h:mn>2.1</h:mn> <h:msub> <h:mi>M</h:mi> <h:mo stretchy="false">⊙</h:mo> </h:msub> </h:math> neutron stars: radii are reduced by about 0.2–0.3 km to values of <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mi>R</k:mi> <k:mn>1.4</k:mn> </k:msub> <k:mo>=</k:mo> <k:mn>12.1</k:mn> <k:mo>±</k:mo> <k:mn>0.5</k:mn> <k:mtext> </k:mtext> <k:mtext> </k:mtext> <k:mi>km</k:mi> </k:math> and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msub> <m:mi>R</m:mi> <m:mn>2.1</m:mn> </m:msub> <m:mo>=</m:mo> <m:msubsup> <m:mn>11.9</m:mn> <m:mrow> <m:mo>−</m:mo> <m:mn>0.6</m:mn> </m:mrow> <m:mrow> <m:mo>+</m:mo> <m:mn>0.5</m:mn> </m:mrow> </m:msubsup> <m:mtext> </m:mtext> <m:mtext> </m:mtext> <m:mi>km</m:mi> </m:math> (at the 68% level), and central densities increase slightly to values of <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>n</o:mi> <o:mi>c</o:mi> </o:msub> <o:mo stretchy="false">(</o:mo> <o:mn>1.4</o:mn> <o:msub> <o:mi>M</o:mi> <o:mo stretchy="false">⊙</o:mo> </o:msub> <o:mo stretchy="false">)</o:mo> <o:mo>/</o:mo> <o:msub> <o:mi>n</o:mi> <o:mn>0</o:mn> </o:msub> <o:mo>=</o:mo> <o:mn>2.8</o:mn> <o:mo>±</o:mo> <o:mn>0.3</o:mn> </o:math> and <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"> <t:msub> <t:mi>n</t:mi> <t:mi>c</t:mi> </t:msub> <t:mo stretchy="false">(</t:mo> <t:mn>2.1</t:mn> <t:msub> <t:mi>M</t:mi> <t:mo stretchy="false">⊙</t:mo> </t:msub> <t:mo stretchy="false">)</t:mo> <t:mo>/</t:mo> <t:msub> <t:mi>n</t:mi> <t:mn>0</t:mn> </t:msub> <t:mo>=</t:mo> <t:msubsup> <t:mn>3.8</t:mn> <t:mrow> <t:mo>−</t:mo> <t:mn>0.7</t:mn> </t:mrow> <t:mrow> <t:mo>+</t:mo> <t:mn>0.6</t:mn> </t:mrow> </t:msubsup> </t:math> (in units of equilibrium nuclear matter density, <y:math xmlns:y="http://www.w3.org/1998/Math/MathML" display="inline"> <y:msub> <y:mi>n</y:mi> <y:mn>0</y:mn> </y:msub> <y:mo>=</y:mo> <y:mn>0.16</y:mn> <y:mtext> </y:mtext> <y:mtext> </y:mtext> <y:msup> <y:mrow> <y:mi>fm</y:mi> </y:mrow> <y:mrow> <y:mo>−</y:mo> <y:mn>3</y:mn> </y:mrow> </y:msup> </y:math> )—i.e., they still fall below five times nuclear saturation density at the 68% level. As a further significant result, the evidence established by analyzing Bayes factors for a trace anomaly measure, <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"> <ab:mi mathvariant="normal">Δ</ab:mi> <ab:mo>=</ab:mo> <ab:mn>1</ab:mn> <ab:mo>/</ab:mo> <ab:mn>3</ab:mn> <ab:mo>−</ab:mo> <ab:mi>P</ab:mi> <ab:mo>/</ab:mo> <ab:mi>ϵ</ab:mi> <ab:mo><</ab:mo> <ab:mn>0</ab:mn> </ab:math> , inside heavy neutron stars is raised to .