A link between White Dwarf pulsars and polars: Multiwavelength observations of the 9.36-minute period variable Gaia22ayj Rodriguez, Antonio C. El-Badry, Kareem Hakala, Pasi Rodríguez-Gil, Pablo Bao, Tong Galiullin, Ilkham Kurlander, Jacob A. Law, Casey J. Pelisoli, Ingrid Schreiber, Matthias R. Burdge, Kevin Caiazzo, Ilaria ; https://orcid.org/0000-0002-4770-5388 Roestel, Jan Van Szkody, Paula Drake, Andrew J. Buckley, David A.H. Potter, Stephen B. Gaensicke, Boris Mori, Kaya Bellm, Eric C. Kulkarni, Shrinivas R. Prince, Thomas A. Graham, Matthew Kasliwal, Mansi M. Rose, Sam Sharma, Yashvi Ahumada, Tomás Anand, Shreya Viitanen, Akke Wold, Avery Chen, Tracy X. Riddle, Reed Smith, Roger ddc:520 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 (math formular) 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 (math formular 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 (math formular) in the 0.3–8 keV energy range, while two very large array radio campaigns resulted in a non-detection with a Fr < 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. IOP Publishing 2025 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/19439 https://research-explorer.ista.ac.at/download/19439/19455 Rodriguez AC, El-Badry K, Hakala P, et al. A link between White Dwarf pulsars and polars: Multiwavelength observations of the 9.36-minute period variable Gaia22ayj. <i>Publications of the Astronomical Society of the Pacific</i>. 2025;137(2). doi:<a href="https://doi.org/10.1088/1538-3873/adb0f1">10.1088/1538-3873/adb0f1</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1088/1538-3873/adb0f1 info:eu-repo/semantics/altIdentifier/issn/0004-6280 info:eu-repo/semantics/altIdentifier/wos/001427877700001 info:eu-repo/semantics/altIdentifier/arxiv/2501.01490 info:eu-repo/semantics/openAccess