Measuring the masses of magnetic white dwarfs: a NuSTAR legacy survey

Creators: Shaw, A. W.; Heinke, C. O.; Mukai, K.; Tomsick, J. A.; Doroshenko, V.; Suleimanov, V. F.; Buisson, D. J. K.; Gandhi, P.; Grefenstette, B. W.; Hare, J.; Jiang, J.; Ludlam, R. M.; Rana, V.; Sivakoff, G. R.

Abstract

The hard X-ray spectrum of magnetic cataclysmic variables can be modelled to provide a measurement of white dwarf mass. This method is complementary to radial velocity measurements, which depend on the (typically rather uncertain) binary inclination. Here, we present results from a Legacy Survey of 19 magnetic cataclysmic variables with NuSTAR. We fit accretion column models to their 20–78 keV spectra and derive the white dwarf masses, finding a weighted average M¯_(WD) = 0.77±0.02 M_⊙, with a standard deviation σ = 0.10 M_⊙, when we include the masses derived from previous NuSTAR observations of seven additional magnetic cataclysmic variables. We find that the mass distribution of accreting magnetic white dwarfs is consistent with that of white dwarfs in non-magnetic cataclysmic variables. Both peak at a higher mass than the distributions of isolated white dwarfs and post-common-envelope binaries. We speculate as to why this might be the case, proposing that consequential angular momentum losses may play a role in accreting magnetic white dwarfs and/or that our knowledge of how the white dwarf mass changes over accretion–nova cycles may also be incomplete.

Additional Information

© 2020 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2020 August 19. Received 2020 August 14; in original form 2020 June 26. We would like to thank the anonymous referee for useful comments that helped improve the manuscript. We also thank Fiona Harrison and the NuSTAR team for approving the mCV Legacy programme. AWS would like to thank Rich Plotkin for useful discussions regarding some of the results in this work. AWS would also like to thank Phil Uttley, Abigail Stevens, and Peter Bult for advice regarding timing analysis. COH acknowledges support from NSERC Discovery grant RGPIN-2016-04602, and a Discovery Accelerator Supplement. VD and VFS thank the Russian Science Foundation (grant 19-12-00423) for financial support. VFS also thanks Deutsche Forschungsgemeinschaft for financial support (grant WE 1312/51-1). DJKB acknowledges support from the Royal Society. BWG acknowledges support under NASA contract No. NNG08FD60C. JH acknowledges support from an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by the USRA through a contract with NASA. JJ acknowledges support by the Tsinghua Shuimu Fellowship and the Tsinghua Astrophysics Outstanding Fellowship. RML acknowledges the support of NASA through Hubble Fellowship Program grant HST-HF2-51440.001. GRS acknowledges support from an NSERC Discovery grant (RGPIN-2016-06569). This work has used data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has used the NuSTARDAS jointly developed by the ASI Science Data Center (Italy) and the California Institute of Technology (USA). This research has used data and/or software provided by the High Energy Astrophysics Science Archive Research Center, which is a service of the Astrophysics Science Division at NASA/GSFC. DATA AVAILABILITY STATEMENT. The data underlying this article are publicly available in the NuSTAR Master Catalog (NUMASTER) at https://heasarc.gsfc.nasa.gov/W3Browse/nustar/numaster.html. The Observation ID for each target is listed in Table 1.

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