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Direct evidence for shock-powered optical emission in a nova

Abstract

Classical novae are thermonuclear explosions that occur on the surfaces of white dwarf stars in interacting binary systems1. It has long been thought that the luminosity of classical novae is powered by continued nuclear burning on the surface of the white dwarf after the initial runaway2. However, recent observations of gigaelectronvolt γ-rays from classical novae have hinted that shocks internal to the nova ejecta may dominate the nova emission. Shocks have also been suggested to power the luminosity of events as diverse as stellar mergers3, supernovae4 and tidal disruption events5, but observational confirmation has been lacking. Here we report simultaneous space-based optical and γ-ray observations of the 2018 nova V906 Carinae (ASASSN-18fv), revealing a remarkable series of distinct correlated flares in both bands. The optical and γ-ray flares occur simultaneously, implying a common origin in shocks. During the flares, the nova luminosity doubles, implying that the bulk of the luminosity is shock powered. Furthermore, we detect concurrent but weak X-ray emission from deeply embedded shocks, confirming that the shock power does not appear in the X-ray band and supporting its emergence at longer wavelengths. Our data, spanning the spectrum from radio to γ-ray, provide direct evidence that shocks can power substantial luminosity in classical novae and other optical transients.

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Fig. 1: Nova V906 Car was discovered in a complex region of the Galaxy near the Carina nebula and the red giant star HD 92063, which was being monitored by the BRITE satellite constellation.
Fig. 2: The optical and GeV γ-ray light curves of nova V906 Car are correlated, showing simultaneous flares in both bands.

Data availability

The data that support the plots within this paper and other findings of this study are available from http://scan.sai.msu.ru/~kirx/v906car/ or from the corresponding authors upon reasonable request.

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Acknowledgements

E.A., L.C. and K.V.S. acknowledge NSF award AST-1751874, NASA award 11-Fermi 80NSSC18K1746 and a Cottrell fellowship of the Research Corporation. K.L.L. was supported by the Ministry of Science and Technology of Taiwan through grant 108-2112-M-007-025-MY3. J.S. was supported by the Packard Foundation. O.P. was supported by Horizon 2020 ERC Starting Grant ‘Cat-In-hAT’ (grant agreement number 803158) and INTER-EXCELLENCE grant LTAUSA18093 from the Czech Ministry of Education, Youth, and Sports. Support for K.J.S. was provided by NASA through the Astrophysics Theory Program (NNX17AG28G). G.A.W. acknowledges Discovery Grant support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. A.F.J.M. is grateful for financial assistance from NSERC (Canada) and FQRNT (Quebec). A.Pigulski acknowledges support provided by the Polish National Science Center (NCN) grant No.number 2016/21/B/ST9/01126. A.Popowicz was supported by statutory activities grant SUT 02/010/BKM19 t.20. D.A.H.B. gratefully acknowledge the receipt of research grants from the National Research Foundation (NRF) of South Africa. A.Kniazev acknowledges the National Research Foundation of South Africa and the Russian Science Foundation (project no.14-50-00043). R.K., W.W. and K.Z. acknowledge support from the Austrian Space Application Programme (ASAP) of the Austrian Research Promotion Agency (FFG). I.V. acknowledges the support by the Estonian Research Council grants IUT26-2 and IUT40-2, and by the European Regional Development Fund (TK133). This research has been partly founded by the National Science Centre, Poland, through grant OPUS 2017/27/B/ST9/01940 to J.M. This work is based on data collected by the BRITE Constellation satellite mission, designed, built, launched, operated and supported by the Austrian Research Promotion Agency (FFG), the University of Vienna, the Technical University of Graz, the University of Innsbruck, the Canadian Space Agency (CSA), the University of Toronto Institute for Aerospace Studies (UTIAS), the Foundation for Polish Science and Technology (FNiTP MNiSW) and National Science Centre (NCN). G.H. is indebeted to the Polish National Science Center for funding by grant number 2015/18/A/ST9/00578. C.S.K. is supported by NSF grants AST-1908952 and AST-1814440. We acknowledge the use of public data from the Swift data archive. UK funding for the Neil Gehrels Swift Observatory is provided by the UK Space Agency. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory. A part of this work is based on observations made with the Southern African Large Telescope (SALT), under the Large science Programme on transient 2018-2-LSP-001. Polish participation in SALT is funded by grant number MNiSW DIR/WK/2016/07. The Australia Telescope Compact Array is part of the Australia Telescope National Facility, which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge ARAS observers T. Bohlsen, B. Heathcote and P. Luckas for their optical spectroscopic observations which complement our database. Nova research at Stony Brook is supported in part by NSF grant AST 1614113, and by research support from Stony Brook University. We thank E. R. Colmenero for initiating the collaboration that has led to this paper.

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E.A. wrote the text. A.Pigulski, A.Popowicz, R.K., K.V.S., L.C., S.R., M.F., R.A., P.Manojlović, R.L.d.O., J.S., K.L.L., A.Kniazev, L.I., F.M.W. and K.R.P. obtained and reduced the data. All authors contributed to the interpretation of the data and commented on the final manuscript.

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Correspondence to Elias Aydi, Kirill V . Sokolovsky or Laura Chomiuk.

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Aydi, E., Sokolovsky, K.V., Chomiuk, L. et al. Direct evidence for shock-powered optical emission in a nova. Nat Astron 4, 776–780 (2020). https://doi.org/10.1038/s41550-020-1070-y

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