A sibling of AR Scorpii: SDSS J230641.47+244055.8 and the observational blueprint of white dwarf pulsars

ABSTRACT Radio pulsating white dwarf (WD) systems, known as WD pulsars, are binary systems where the rapidly spinning WD interacts with a low-mass companion, producing pulsed non-thermal emission observed across the entire electromagnetic spectrum. Only two such systems are known: AR Sco and eRASSU J191213.9–441044. Here, we present the discovery of a third WD pulsar, SDSS J230641.47$+$244055.8. The optical spectrum is dominated by molecular bands from an M-dwarf companion, with additional narrow Balmer and He i lines. The long-term optical light curve folded on its orbital period ($P_\mathrm{orb} = 3.49$ h) shows $\sim 10$ per cent scatter. High-cadence photometry reveals a short-period signal, which we interpret to be the spin period of the WD primary ($P_\mathrm{spin} \simeq 92$ s). The WD spin period is slightly shorter than that of AR Sco ($\rm \sim 117$ s), the WD pulsar prototype. Time-resolved spectroscopy reveals emission from the irradiated companion and Na i absorption tracing its centre of mass, yielding a binary mass function of $f(M) \simeq 0.2\, {\rm M_\odot }$. The H$\alpha$ emission includes a low-amplitude broad component, resembling the energetic flashes seen in AR Sco. Using spectral templates, we classify the companion to be most likely a $\rm M4.0\pm 0.5$ with $T_\mathrm{\rm eff} \approx 3300$ K. Modelling the stellar contribution constrains the secondary mass ($0.19\, \mathrm{M}_\odot \lesssim M_2\lesssim 0.28\, \mathrm{M}_\odot$), distance ($\simeq 1.2\, {\rm kpc}$), and inclination ($i \simeq 45^\circ-50^\circ$). We discuss the proposed evolutionary scenarios and summarize the observational properties of all three known WD pulsars, establishing a benchmark for identifying and classifying future members of this class.

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Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-09-12
DOI
https://doi.org/10.1093/mnras/staf1511
Citations
4
Primary Topic
Pulsars and Gravitational Waves Research
Type
article
Field-Weighted Citation Impact
4.62

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article

A sibling of AR Scorpii: SDSS J230641.47+244055.8 and the observational blueprint of white dwarf pulsars

S. P. Littlefair, James Munday, J. McCormac, Noel Castro Segura et al.
4 citations
Monthly Notices of the Royal Astronomical Society
Pulsars and Gravitational Waves Research
4.62
article

A sibling of AR Scorpii: SDSS J230641.47+244055.8 and the observational blueprint of white dwarf pulsars

S. P. Littlefair, James Munday, J. McCormac, Noel Castro Segura, A. Sahu, Danny T. H. Steeghs, Mark R Kennedy, Deborah Jarvis, Keith Inight, D. I. Sahman, D. A. H. Buckley, D. L. Coppejans, A. Romero, Ingrid Pelisoli, V. S. Dhillon, Martin J. Dyer, S. G. Parsons, A. Aungwerojwit, Matthew Green, J. A. Garbutt, P. Kerry, Boris T. Gänsicke, Alex Brown, E. R. Pike
article en
4 citations

Abstract

ABSTRACT Radio pulsating white dwarf (WD) systems, known as WD pulsars, are binary systems where the rapidly spinning WD interacts with a low-mass companion, producing pulsed non-thermal emission observed across the entire electromagnetic spectrum. Only two such systems are known: AR Sco and eRASSU J191213.9–441044. Here, we present the discovery of a third WD pulsar, SDSS J230641.47$+$244055.8. The optical spectrum is dominated by molecular bands from an M-dwarf companion, with additional narrow Balmer and He i lines. The long-term optical light curve folded on its orbital period ($P_\mathrm{orb} = 3.49$ h) shows $\sim 10$ per cent scatter. High-cadence photometry reveals a short-period signal, which we interpret to be the spin period of the WD primary ($P_\mathrm{spin} \simeq 92$ s). The WD spin period is slightly shorter than that of AR Sco ($\rm \sim 117$ s), the WD pulsar prototype. Time-resolved spectroscopy reveals emission from the irradiated companion and Na i absorption tracing its centre of mass, yielding a binary mass function of $f(M) \simeq 0.2\, {\rm M_\odot }$. The H$\alpha$ emission includes a low-amplitude broad component, resembling the energetic flashes seen in AR Sco. Using spectral templates, we classify the companion to be most likely a $\rm M4.0\pm 0.5$ with $T_\mathrm{\rm eff} \approx 3300$ K. Modelling the stellar contribution constrains the secondary mass ($0.19\, \mathrm{M}_\odot \lesssim M_2\lesssim 0.28\, \mathrm{M}_\odot$), distance ($\simeq 1.2\, {\rm kpc}$), and inclination ($i \simeq 45^\circ-50^\circ$). We discuss the proposed evolutionary scenarios and summarize the observational properties of all three known WD pulsars, establishing a benchmark for identifying and classifying future members of this class.

Monthly Notices of the Royal Astronomical SocietyVol. 543(3)
Universidade Federal do Rio Grande do Sul (BR), National Institute of Standards and Technology (US), University of Cape Town (ZA), Universität Hamburg (DE), University College Cork (IE), University of Warwick (GB), Physical Sciences (United States) (US), South African Radio Astronomy Observatory (ZA), Instituto de Astrofísica de Canarias (ES), Naresuan University (TH), University of Oklahoma (US), University of Sheffield (GB)
National Science Foundation, Smithsonian Institution, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Ohio State University, California Institute of Technology, Northwestern University, Harvard University, Johns Hopkins University, Drexel University, New Mexico State University, Space Telescope Science Institute, National Astronomical Research Institute of Thailand, Flatiron Health, University of Warwick, European Commission, École Polytechnique Fédérale de Lausanne, University of Toronto, Korea Astronomy and Space Science Institute, Naresuan University, Universidad Nacional Autónoma de México, Yunnan University, Nanjing University, Stockholms Universitet, China National Textile and Apparel Council, Ministério da Ciência, Tecnologia, Inovações e Comunicações, Leibniz-Institut für Astrophysik Potsdam, Agencia Nacional de Investigación y Desarrollo, Max-Planck-Institut für Astronomie, University of Illinois at Urbana-Champaign, University of Colorado Boulder, Smithsonian Astrophysical Observatory, Science and Technology Facilities Council, Leibniz-Gemeinschaft, National Astronomical Observatories, Chinese Academy of Sciences
Openalex Percentile: Top 5%
Pulsars and Gravitational Waves Research
4.62
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