Recurrent nova M31N 2008-12a: Swift/XRT and Swift/UVOT detections of the 2022 eruption

ATel #15798; M. J. Darnley (LJMU), K. L. Page (Leicester), M. W. Healy (LJMU), on behalf of the 12a collaboration
on 8 Dec 2022; 10:01 UT
Credential Certification: Matt Darnley (matt_darnley@icloud.com)

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The 2022 eruption of the annual recurrent nova M31N 2008-12a was reported in ATel #15786, with spectroscopic confirmation report in ATel #15788. Subsequent observations have also been reported in ATels #15787, #15789, #15790, #15795, and #15797.

Based on comparison with optical data from the 2013-2021 eruption, we tentatively estimate the onset of the 2022 eruption occurred at MJD 59915.83 (2022-12-02.83 UT), consistent with the discovery observation (ATel #15786).

A Neil Gehrels Swift Observatory target-of-opportunity programme was approved on December 3rd to follow the UV evolution and X-ray super-soft source turn-on.

The first Swift/UVOT observation took place on December 3rd and clearly detected the eruption with a uvw2 magnitude of 17.00 ± 0.04 mag (Vega).

Subsequently, Swift has observed the source with a daily cadence and the UV brightness has faded in-line with previous observations.

Swift/XRT did not detect any source at the position of M31N 2008-12a until late on December 7th.

The last XRT non-detection was at a level of < 0.015 count s^-1 (0.3-10 keV; 90% confidence), in 934 s of data. This was at 2022-12-07 15:24 - 15:39 (MJD 59920.641544 - 59920.652396)

Alternatively, we have a deeper non-detection of < 0.0038 count s^-1 (0.3-10 keV; 90% confidence), in 4.1 ks summed over 2022-12-07 01:05 - 15:39 (MJD 59920.045684 - 59920.652396).

The actual first detection, at a level of (3.2 +0.8/-0.6)e-3 count s^-1, was in 1.04 ks of data from 23:20-23:39 UT (MJD 59920.97277 - 59920.98571).

Based on the estimated time of eruption, the super-soft source turn-on occurred at approximately t = 5.2 days.

We wish to thank the Swift Team for the extremely rapid and efficient scheduling of the ToO observations, in particular the duty scientists, and the science planners