A Link Between White Dwarf Pulsars and Polars: Multiwavelength Observations of the 9.36-minute Period Variable Gaia22ayj

Creators: Rodriguez, Antonio C.¹; El-Badry, Kareem¹; Hakala, Pasi²; Rodríguez-Gil, Pablo^{3, 4}; Bao, Tong⁵; Galiullin, Ilkham⁶; Kurlander, Jacob A.⁷; Law, Casey J.¹; Pelisoli, Ingrid⁸; Schreiber, Matthias R.⁹; Burdge, Kevin¹⁰; Caiazzo, Ilaria¹¹; Roestel, Jan van¹²; Szkody, Paula⁷; Drake, Andrew J.¹; Buckley, David A. H.^{13, 14, 15}; Potter, Stephen B.^{13, 16}; Gaensicke, Boris⁸; Mori, Kaya¹⁷; Bellm, Eric C.⁷; Kulkarni, Shrinivas R.¹; Prince, Thomas A.¹; Graham, Matthew¹; Kasliwal, Mansi M.¹; Rose, Sam¹; Sharma, Yashvi¹; Ahumada, Tomás¹; Anand, Shreya^{1, 18}; Viitanen, Akke^{19, 20}; Wold, Avery²¹; Chen, Tracy X.²¹; Riddle, Reed¹; Smith, Roger¹

1. California Institute of Technology
2. University of Turku
3. Instituto de Astrofísica de Canarias
4. University of La Laguna
5. INAF—Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
6. Kazan Federal University
7. University of Washington
8. University of Warwick
9. Federico Santa María Technical University
10. Massachusetts Institute of Technology
11. Institute of Science and Technology Austria
12. University of Amsterdam
13. South African Radio Astronomy Observatory
14. University of Cape Town
15. University of the Free State
16. University of Johannesburg
17. Columbia University
18. Stanford University
19. Astronomical Observatory of Rome
20. University of Helsinki
21. Infrared Processing and Analysis Center

Abstract

White dwarfs (WDs) are the most abundant compact objects, and recent surveys have suggested that over a third of WDs in accreting binaries host a strong (B ≳ 1 MG) magnetic field. However, the origin and evolution of WD magnetism remain under debate. Two WD pulsars, AR Sco and J191213.72–441045.1 (J1912), have been found, which are non-accreting binaries hosting rapidly spinning (1.97 minutes and 5.30 minutes, respectively) magnetic WDs. The WD in AR Sco is slowing down on a P/P˙≈5.6×10⁶ yr timescale. It is believed they will eventually become polars, accreting systems in which a magnetic WD (B ≈ 10−240 MG) accretes from a Roche lobe-filling donor spinning in sync with the orbit (≳78 minutes). Here, we present multiwavelength data and analysis of Gaia22ayj, which outbursted in 2022 March. We find that Gaia22ayj is a magnetic accreting WD that is rapidly spinning down (P/P˙=6.1_(−0.2)^(+0.3)×10⁶ yr) like WD pulsars, but shows clear evidence of accretion, like polars. Strong linear polarization (40%) is detected in Gaia22ayj; such high levels have only been seen in the WD pulsar AR Sco and demonstrate the WD is magnetic. High speed photometry reveals a 9.36 minutes period accompanying a high amplitude (∼2 mag) modulation. We associate this with a WD spin or spin–orbit beat period, not an orbital period as was previously suggested. Fast (60 s) optical spectroscopy reveals a broad "hump," reminiscent of cyclotron emission in polars, between 4000 and 8000 Å. We find an X-ray luminosity of L_X=2.7_(−0.8)^(+6.2)×10³²ergs⁻¹ in the 0.3–8 keV energy range, while two very large array radio campaigns resulted in a non-detection with a F_r < 15.8 μJy 3σ upper limit. The shared properties of both WD pulsars and polars suggest that Gaia22ayj is a missing link between the two classes of magnetic WD binaries.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We wish to dedicate this work to the memory of our colleague and friend Tom Marsh. Tom's enthusiasm to work on this object and rapid efforts to facilitate data collection truly made this project possible.

A.C.R. acknowledges support from an NSF Graduate Fellowship. A.C.R. thanks the LSST-DA Data Science Fellowship Program, which is funded by LSST-DA, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. P.R.-G. acknowledges support by the Spanish Agencia Estatal de Investigación del Ministerio de Ciencia e Innovación (MCIN/AEI) and the European Regional Development Fund (ERDF) under grant PID2021–124879NB–I00. M.R.S. is supported by FONDECYT (grant No. 1221059) and eRO-STEP (SA 2131/15-2 project number 414059771). I.P. acknowledges support from a Royal Society University Research Fellowship (URF/R1/231496). We thank the referee for feedback that improved the clarity of this paper.

Based on observations made with the Gran Telescopio Canarias (GTC), installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofìsica de Canarias, on the island of La Palma. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the ZTF project. ZTF is supported by the National Science Foundation under grants No. AST-1440341 and AST-2034437 and a collaboration including current partners Caltech, IPAC, the Weizmann Institute of Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, IN2P3, University of Warwick, Ruhr University Bochum, Northwestern University and former partners the University of Washington, Los Alamos National Laboratories, and Lawrence Berkeley National Laboratories. Operations are conducted by COO, IPAC, and UW.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. We are also grateful to the staff of Palomar Observatory for their assistance in carrying out observations used in this work.

Partly based on observations made with the NOT, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. The data presented here were obtained with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOT. The observation with the SALT was obtained under program 2021-2-LSP-001 (PI: D. Buckley). Polish participation in SALT is funded by grant No. MEiN nr 2021/WK/01. D.A.H.B. acknowledges support from the National Research Foundation.

This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia archive website is https://archives.esac.esa.int/gaia. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester

E.C.B. and J.K. acknowledge support from the DIRAC Institute in the Department of Astronomy at the University of Washington. The DIRAC Institute is supported through generous gifts from the Charles and Lisa Simonyi Fund for Arts and Sciences, and the Washington Research Foundation.

Files

Rodriguez_2025_PASP_137_024202.pdf

Files (3.3 MB)

Name	Size	Download all
Rodriguez_2025_PASP_137_024202.pdf md5:42d5aa504479c3fdf2a10165a9e3319f	3.3 MB	Preview Download

	All versions	This version
Views	0	0
Downloads	0	0
Data volume	0 Bytes	0 Bytes

A Link Between White Dwarf Pulsars and Polars: Multiwavelength Observations of the 9.36-minute Period Variable Gaia22ayj

Abstract

Copyright and License

Acknowledgement

Files

Additional details