A1 Refereed original research article in a scientific journal
Parameter constraints for accreting millisecond pulsars with synthetic NICER data
Authors: Dorsman, Bas; Salmi, Tuomo; Watts, Anna L.; Ng, Mason; Kamath, Satish; Bobrikova, Anna; Poutanen, Juri; Loktev, Vladislav; Kini, Yves; Choudhury, Devarshi; Vinciguerra, Serena; Bogdanov, Slavko; Chakrabarty, Deepto
Publisher: Oxford University Press (OUP)
Publishing place: OXFORD
Publication year: 2025
Journal: Monthly Notices of the Royal Astronomical Society
Journal name in source: Monthly Notices of the Royal Astronomical Society
Journal acronym: MON NOT R ASTRON SOC
Volume: 538
Issue: 4
First page : 2853
Last page: 2868
Number of pages: 16
ISSN: 0035-8711
eISSN: 1365-2966
DOI: https://doi.org/10.1093/mnras/staf438
Web address : https://doi.org/10.1093/mnras/staf438
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/491603979
Pulse profile modelling (PPM) is a technique for inferring mass, radius, and hotspot properties of millisecond pulsars. PPM is now regularly used for the analysis of rotation-powered millisecond pulsars with data from the Neutron Star Interior Composition ExploreR (NICER). Extending PPM to accreting millisecond pulsars (AMPs) is attractive, because they are a different source class featuring bright X-ray radiation from hotspots powered by accretion. In this paper, we present a modification of one of the PPM codes, x-psi, so that it can be used for AMPs. In particular, we implement a model of an accretion disc and atmosphere model appropriate for the hotspots of AMPs, and improve the overall computational efficiency. We then test parameter recovery with simulated NICER data in two scenarios with reasonable parameters for AMPs. We find in the first scenario, where the hotspot is large, that we are able to tightly and accurately constrain all parameters including mass and radius. In the second scenario, which is a high inclination system with a smaller hotspot, we find slightly widened posteriors, degeneracy between a subset of model parameters, and a slight bias in the inferred mass. This analysis of synthetic data lays the ground work for future analysis of AMPs with NICER data. Such an analysis could be complemented by future (joint) analysis of polarization data from the Imaging X-ray Polarimetry Explorer.
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Funding information in the publication:
BD thanks Rudy Wijnands, Phil Uttley, Matteo Lucchini, Evert Rol, and Martin Heemskerk for fruitful discussions and advice. BD thanks Duncan Galloway for interesting discussions and estimates for the distance of J1808. BD, TS, ALW, YK, DC, and SV acknowledge support from ERC Consolidator grant No. 865768 AEONS (PI: Watts). MN is a Fonds de Recherche du Quebec-Nature et Technologies (FRQNT) postdoctoral fellow. JP thanks the Academy of Finland grant 333112 and the Ministry of Science and Higher Education grant 075-15-2024-647. AB was supported by the Finnish Cultural Foundation grant 00240328. This work used the Dutch national e-infrastructure with the support of the SURF Cooperative using grant no. EINF-5867. Part of the work was carried out on the HELIOS cluster including dedicated nodes funded via the above-mentioned ERC CoG. We acknowledge extensive use of NASA's Astrophysics Data System (ADS) Bibliographic Services and the ArXiv. Software: x-psi (Riley et al. 2023), gnu scientific library (gsl; Gough 2009), heasoft (NASA/GSFC High Energy Astrophysics Science Archive Research Center 2014), mpi for python (Dalcin et al. 2008), multinest (Feroz et al. 2009), pymultinest (Buchner et al. 2014), nestcheck (Higson 2018), getdist (Lewis 2019), jupyter (Perez & Granger 2007; Kluyver et al. 2016), astropy (Astropy Collaboration 2013, 2018, 2022), scipy (Virtanen et al. 2020; Gommers et al. 2024), matplotlib (Hunter 2007), numpy (Harris et al. 2020), python (Van Rossum & Drake 2009), cython (Behnel et al. 2011), and spyder (Spyder Development Team 2024).
