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Recurrent nova M31N 2008-12a: deep Liverpool Telescope and Swift photometry of the 2015 eruption

ATel #8029; M. J. Darnley (LJMU), M. Henze (IEEC/CSIC), A. W. Shafter (SDSU), M. Kato (Keio University), for a larger collaboration
on 9 Sep 2015; 16:43 UT
Credential Certification: Matt Darnley (M.J.Darnley@ljmu.ac.uk)

Subjects: Optical, Nova, Transient

Referred to by ATel #: 8033, 8062

In ATel #7964 we reported the discovery of the 2015 eruption of the recurrent nova M31N 2008-12a on 2015-08-28.55 UT. Comprehensive multi-wavelength studies of previous eruptions were published by Darnley et al. 2014, 2015, and Henze et al. 2014, 2015a. For additional optical photometry of the ongoing eruption see ATels #7965, #7967, #7968, #7969, #7974, #7976, #7979, #7980, and #7984. This is the 8th outburst of M31N 2008-12a in 8 consecutive years (Henze et al. 2015b).

Deep photometric observations of the 2015 eruption were made using the Liverpool Telescope on the night of 2015 Sep 8 UT, at approximately 10.75 days post maximum light. The nova was still clearly detected in the Sloan u', B, and V-bands, with the Sloan r', i', and z'-bands providing (3 sigma) upper limits:

2015 Sep 9.058 u' = 22.2 ± 0.2
2015 Sep 9.074 B = 22.70 ± 0.09
2015 Sep 9.091 V = 22.5 ± 0.1
2015 Sep 9.107 r' > 22.7
2015 Sep 9.121 i' > 22.1
2015 Sep 9.132 z' > 22.1

The first of four weekly HST WFC3/UVIS imaging visits, following the late decline phase of the nova, is scheduled between Sep 10.55 and Sep 10.72 UT. We encourage simultaneous ground-based observations by any facility capable of deep observations of the M31 field.

Following ATel #7984, the Swift UV magnitudes have now faded considerably. We estimated a preliminary uvw1 filter (181-321 nm) magnitude of 21.8 ± 0.8 mag based on 4.4 ks of Swift exposure centred on 2015 Sep 8.57 UT. The corresponding X-ray count rates and temperatures were in good agreement with the 2014 results presented by Henze et al. (2015a).

We wish to thank the Swift Science Operations Team for making these observations possible, in particular the duty scientists and the science planners.