Recurrent nova M31N 2008-12a: Swift/XRT detection of the SSS following the 2025 eruption

ATel #17526; M. J. Darnley (LJMU), K. L Page (U. Leicester)
on 5 Dec 2025; 10:27 UT
Credential Certification: Matt Darnley (matt_darnley@icloud.com)

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The 2025 eruption of the annual recurrent nova M31N 2008-12a was first reported in ATel #17511 (also see ATel #17514, #17520, #17521, #17524). Target of opportunity observations by the Neil Gehrels Swift Observatory began shortly after the eruption was confirmed (and continue).

Data collected 4.8 days after the eruption (see timing estimation from ATel #17514) show the emergence of the supersoft X-ray source (SSS) phase of the 2025 eruption. In the corresponding Swift snapshot an X-ray source with a count rate of 3.0 +0.9/-0.7 milli-counts per second was detected.

The previous snapshot, taken just 0.2 days earlier revealed a non-detection (0 photons).

The timing of the 2025 SSS and the spectrum (albeit based on only 8 photons) is consistent with all previous eruptions.

We thanks the Swift PIs, duty scientists and science planners for their rapid approval and scheduling of these observations.