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arXiv · 2610.33844

Far Ultraviolet Variability on Timescales of a Few hours in the Recurrent Nova M31N 2008-12a: Origin and Implications

Judhajeet Basu·Sudhanshu Barway·G. C. Anupama·Shatakshi Chamoli·Kulinder Pal Singh·Varun Bhalerao·M. Pavana·Vishwajeet Swain
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Abstract

The fate of the accretion disk during nova eruptions remains an open question, particularly in rapidly recurring novae, where high accretion rates and low ejecta masses may allow the disk to survive the eruption. M31N 2008-12a, the most rapidly recurring nova currently known, provides an ideal laboratory for investigating this process. We present high-cadence AstroSat/UVIT observations obtained during eruptions between 2019 and 2023. Complementary multiwavelength observations of the 2023-2025 eruptions are also presented, which are broadly consistent with prior outbursts. The main result is the early onset of intrinsic far-ultraviolet variability on a timescale of a few hours, approximately 4-5 days after eruption, which is of astrophysical origin. A periodicity search suggests a tentative signal at 4.60 (+0.25,-0.15) hr at 2.3 sigma confidence, detected in high-cadence UVIT/FUV observations. We show that a Keplerian orbit of this timescale lies not only within the Roche lobe of the white dwarf in M31N 2008-12a, but also within the circularisation radius. A disk-related origin is, thus, physically plausible. The presence of this UV variability so soon after eruption suggests that accretion structures may already exist during the early post-eruption phase, supporting the disk-survival hypotheses. If confirmed by future observations, this method may provide a new dynamical probe of accretion disk survival in rapidly recurring novae.

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Judhajeet Basu, Sudhanshu Barway, G. C. Anupama, Shatakshi Chamoli, Kulinder Pal Singh, Varun Bhalerao, M. Pavana, Vishwajeet Swain. 2026-10-24. Far Ultraviolet Variability on Timescales of a Few hours in the Recurrent Nova M31N 2008-12a: Origin and Implications. https://arxiv.org/abs/2610.33844

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