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Localized thermonuclear bursts from accreting magnetic white dwarfs


Nova explosions are caused by global thermonuclear runaways triggered in the surface layers of accreting white dwarfs1,2,3. It has been predicted4,5,6 that localized thermonuclear bursts on white dwarfs can also take place, similar to type-I X-ray bursts observed in accreting neutron stars. Unexplained rapid bursts from the binary system TV Columbae, in which mass is accreted onto a moderately strong magnetized white dwarf from a low-mass companion, have been observed on several occasions in the past 40 years7,8,9,10,11. During these bursts, the optical/ultraviolet luminosity increases by a factor of more than  three in less than an hour and fades in around ten hours. Fast outflows have been observed in ultraviolet spectral lines7, with velocities of more than 3,500 kilometres per second, comparable to the escape velocity from the white dwarf surface. Here we report on optical bursts observed in TV Columbae and in two additional accreting systems, EI Ursae Majoris and ASASSN-19bh. The bursts have a total energy of approximately 10−6  times than those of classical nova explosions (micronovae) and bear a strong resemblance to type-I X-ray bursts12,13,14. We exclude accretion or stellar magnetic reconnection events as their origin and suggest thermonuclear runaway events in magnetically confined accretion columns as a viable explanation.

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Fig. 1: Optical brightness variations in TV Col.
Fig. 2: Optical brightness variations in EI UMa and ASASSN-19bh.

Data availability

The data collected by the TESS mission used in this study can be obtained from MAST in reduced and calibrated format ( The ASAS-SN g- and V-band magnitudes can be obtained from the ASAS-SN Sky Patrol webpage ( The RXTE-PCA data of SAX J1808.4-365 and the EXOSAT-ME data of 4U 1636-536 have been retrieved from the High Energy Astrophysics Science Archive Research Center.


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P.J.G. is supported by the South African National Research Foundation (NRF) SARChI grant no. 111692. D.A.H.B. acknowledges research support from the South African National Research Foundation. D.d.M. acknowledges financial support from the Italian Space Agency (ASI) and National Institute for Astrophysics (INAF) under agreements ASI-INAF I/037/12/0 and ASI-INAF n.2017-14-H.0, and from INAF ‘Sostegno alla ricerca scientifica main streams dell’INAF’, Presidential Decree 43/2018, from INAF ‘SKA/CTA projects’, Presidential Decree 70/2016, and from PHAROS COST Action N.16214. C.D. and K.I. acknowledge funding from the Science and Technology Facilities Council (STFC) consolidator grant no. ST/T000244/1. J.-P.L. was supported in part by a grant from the French Space Agency CNES. P.S. acknowledges support from National Science Foundation (NSF) grant no. AST-1514737. F.X.T. is supported by the NSF under grant no. ACI-1663684 for the MESA Project, and by the NSF under grant no. PHY-1430152 for the Physics Frontier Center Joint Institute for Nuclear Astrophysics Center for the Evolution of the Elements (JINA-CEE). This paper includes data collected by the TESS mission. Funding for the TESS mission is provided by the NASA’s Science Mission Directorate. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract no. NAS5-26555. Support for MAST for non-Hubble Space Telescope data is provided by the NASA Office of Space Science by grant no. NNX09AF08G and by other grants and contracts. This paper uses data from the ASAS-SN project run by the Ohio State University. We thank the ASAS-SN team for making their data publicly available. This work has also made use of data from the European Space Agency mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. The study is based on observations collected at the European Southern Observatory (ESO) under ESO-DDT programme 107.2309.001, for which we acknowledge support from the ESO Director-General.

Author information

Authors and Affiliations



S.S. was principal investigator of the TESS proposal to obtain the data, discovered the bursts and performed the ASAS-SN luminosity calibration, co-developed the application of the bombardment model to potentially drive TNRs and led the interpretation of the bursts. P.J.G. was principal investigator of the X-Shooter proposal to obtain the spectrum of ASASSN-19bh. Y.C. contributed details on the analogy with type-I X-ray bursts, including leading the discussions on their temporal evolution. C.F.M. reduced the X-Shooter spectrum of ASASSN-19bh. S.S., P.J.G., C.K., A.J.B., E.B., D.A.H.B., Y.C., N.D.D., D.d.M., C.D., M.F., K.I., E.K., J.-P.L., C.L., C.F.M., M.O'B., P.S. and F.X.T shared ideas, interpreted the results, commented and edited the manuscript.

Corresponding author

Correspondence to S. Scaringi.

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The authors declare no competing interests.

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Nature thanks Michael Shara and Erik Kuulkers for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 X-Shooter spectrum of ASASSN-19bh.

a. X-Shooter spectrum (UBV arm) in the range 3900 Å-4900 Å. b. X-Shooter spectrum (VIS arm) in the range 5800 Å–6700 Å. Hydrogen Balmer-series lines are marked with the red dashed lines. The HeI 5875 Å is marked with a blue dashed line. CaII H&K emission lines can be seen blueward of 4000 Å. Numerous narrow absorption lines from the secondary are also identifiable. Narrow emission spikes in e.g. the region 6000–6200 Å are residuals from the sky subtraction.

Extended Data Fig. 2 Long term ASAS-SN lightcurves of TV Col, EI UMa, and ASASSN-19bh.

a. ASAS-SN lightcurve of TV Col b. ASASSN lightcurve of EI UMa c. ASASSN lightcurve of ASASSN-19bh. In all panels the blue and red points correspond to ASAS-SN V-band and g-band photometry respectively. Calibrated TESS data points are shown in grey. Typical uncertainties on magnitude are 0.02.

Extended Data Fig. 3 Comparison between Type-I X-ray bursts and micronovae.

a. TESS lightcurve of one of the rapid bursts observed in TV Col. b. TESS lightcurve of the rapid burst observed in ASASSN-19bh. c. EXOSAT-ME X-ray lightcurve of 4U 1636-536 of one of the Type-I X-ray bursts. Note the similar multi-peak structure in both TV Col and 4U 1636-536. d. RXTE-PCA X-ray lightcurve of one rapid burst in SAX J1808.4-3658. Note the precursor present in both ASASSN-19bh and SAX J1808.4-3658. In all panels the time axis has been arbitrarily shifted.

Extended Data Fig. 4 Lomb-Scargle periodograms of TV Col.

Periodograms using TESS data for TV Col a. Cycle 1 (120-s) low frequency periodogram. b. Cycle 1 high frequency periodogram. c. Cycle 3 (20-s) low frequency periodogram. d. Cycle 3 high frequency periodogram. In all panels the dashed-red lines mark the orbital frequency and associated harmonics, while the dashed-blue vertical lines mark the spin-to-orbital beat frequency. The dashed-magenta line marks the superorbital signal. The dashed-green lines mark the detected negative superhump, associated harmonics, and beats with the orbital frequency.

Extended Data Fig. 5 Lomb-Scargle periodograms of EI UMa.

Periodograms using TESS data for EI UMa during Cycle 2 (120-s cadence). a. Low frequency periodogram computed before the bursts. b. High-frequency periodogram computed before the bursts. c. Low-frequency periodogram computed after the bursts. d. High-frequency periodogram computed after the bursts. In all panels the dashed-red vertical line marks the detected orbital frequency. The dashed-blue vertical lines mark the spin-to-orbital beat frequency. The dashed-green line marks the positive superhump frequency.

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Scaringi, S., Groot, P.J., Knigge, C. et al. Localized thermonuclear bursts from accreting magnetic white dwarfs. Nature 604, 447–450 (2022).

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