The Radius of the High-mass Pulsar PSR J0740+6620 with 3.6 yr of NICER Data

Kavli Affiliate: Deepto Chakrabarty

| First 5 Authors: Tuomo Salmi, Devarshi Choudhury, Yves Kini, Thomas E. Riley, Serena Vinciguerra

| Summary:

We report an updated analysis of the radius, mass, and heated surface regions
of the massive pulsar PSR J0740+6620 using Neutron Star Interior Composition
Explorer (NICER) data from 2018 September 21 to 2022 April 21, a substantial
increase in data set size compared to previous analyses. Using a tight mass
prior from radio timing measurements and jointly modeling the new NICER data
with XMM-Newton data, the inferred equatorial radius and gravitational mass are
$12.49_{-0.88}^{+1.28}$ km and $2.073_{-0.069}^{+0.069}$ $M_odot$
respectively, each reported as the posterior credible interval bounded by the
$16,%$ and $84,%$ quantiles, with an estimated systematic error $lesssim
0.1$ km. This result was obtained using the best computationally feasible
sampler settings providing a strong radius lower limit but a slightly more
uncertain radius upper limit. The inferred radius interval is also close to the
$R=12.76_{-1.02}^{+1.49}$ km obtained by Dittmann et al., when they require the
radius to be less than $16$ km as we do. The results continue to disfavor very
soft equations of state for dense matter, with $R<11.15$ km for this high-mass
pulsar excluded at the $95,%$ probability. The results do not depend
significantly on the assumed cross-calibration uncertainty between NICER and
XMM-Newton. Using simulated data that resemble the actual observations, we also
show that our pipeline is capable of recovering parameters for the inferred
models reported in this paper.

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