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Published December 10, 2019 | Accepted Version + Published
Journal Article Open

A NICER View of PSR J0030+0451: Millisecond Pulsar Parameter Estimation


We report on Bayesian parameter estimation of the mass and equatorial radius of the millisecond pulsar PSR J0030+0451, conditional on pulse-profile modeling of Neutron Star Interior Composition Explorer X-ray spectral-timing event data. We perform relativistic ray-tracing of thermal emission from hot regions of the pulsar's surface. We assume two distinct hot regions based on two clear pulsed components in the phase-folded pulse-profile data; we explore a number of forms (morphologies and topologies) for each hot region, inferring their parameters in addition to the stellar mass and radius. For the family of models considered, the evidence (prior predictive probability of the data) strongly favors a model that permits both hot regions to be located in the same rotational hemisphere. Models wherein both hot regions are assumed to be simply connected circular single-temperature spots, in particular those where the spots are assumed to be reflection-symmetric with respect to the stellar origin, are strongly disfavored. For the inferred configuration, one hot region subtends an angular extent of only a few degrees (in spherical coordinates with origin at the stellar center) and we are insensitive to other structural details; the second hot region is far more azimuthally extended in the form of a narrow arc, thus requiring a larger number of parameters to describe. The inferred mass M and equatorial radius R_(eq) are, respectively, 1.34_(-0.16)^(+0.15) M_⊙ and 12.71_(-1.19)^(+1.14) km, while the compactness GM/{R_(eq) c^2= 0.156_(-0.010)^(+0.008) is more tightly constrained; the credible interval bounds reported here are approximately the 16% and 84% quantiles in marginal posterior mass.

Additional Information

© 2019. The American Astronomical Society. Received 2019 July 12; revised 2019 September 24; accepted 2019 September 25; published 2019 December 12. Focus on NICER Constraints on the Dense Matter Equation of State. We thank the anonymous referees for their suggested improvements to this work. This work was supported in part by NASA through the NICER mission and the Astrophysics Explorers Program. T.E.R., A.L.W., and A.V.B. acknowledge support from ERC Starting grant No. 639217 CSINEUTRONSTAR (PI: Watts). A.L.W. would also like to thank Ralph Wijers for environmental support. This work was sponsored by NWO Exact and Natural Sciences for the use of supercomputer facilities, and was carried out on the Dutch national e-infrastructure with the support of SURF Cooperative. This research has made extensive use of NASA's Astrophysics Data System Bibliographic Services (ADS) and the arXiv. R.M.L. acknowledges the support of NASA through Hubble Fellowship Program grant HST-HF2-51440.001. S.G. acknowledges the support of the Centre National d'Études Spatiales (CNES). W.C.G.H. appreciates use of computer facilities at the Kavli Institute for Particle Astrophysics and Cosmology. S.M.M. thanks NSERC for support. J.M.L. acknowledges support from NASA through Grant 80NSSC17K0554 and the U.S. DOE from grant DE-FG02-87ER40317. Facility: NICER (Gendreau et al. 2016). Software: Python/C language (Oliphant 2007), GNU Scientific Library (GSL; Gough 2009), NumPy (van der Walt et al. 2011), Cython (Behnel et al. 2011), SciPy (Jones et al. 2001), OpenMP (Dagum & Menon 1998), MPI (Forum 1994), MPI for Python (Dalcín et al. 2008), Matplotlib (Hunter 2007; Droettboom et al. 2018), IPython (Perez & Granger 2007), Jupyter (Kluyver et al. 2016), tempo2 (photons; Hobbs et al. 2006), PINT (photonphase; https://github.com/nanograv/PINT), MultiNest (Feroz et al. 2009), PyMultiNest (Buchner et al. 2014), GetDist (https://github.com/cmbant/getdist), nestcheck (Higson 2018; Higson et al. 2018, 2019), fgivenx (Handley 2018), X-PSI (v0.1; https://github.com/ThomasEdwardRiley/xpsi; Riley & Watts 2019).

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Published - Riley_2019_ApJL_887_L21.pdf

Accepted Version - 1912.05702.pdf


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