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M31N 2016-08d is a luminous nova candidate in M31 with Swift/UVOT detections

ATel #9408; M. Henze (CSIC-IEEC), K. Hornoch (Ondrejov), S. C. Williams (Lancaster), M. J. Darnley (LJMU), A. W. Shafter (SDSU), J. Vrastil, H. Kucakova, K. Honkova (all Charles University), M. J. Middleton (Cambridge)
on 25 Aug 2016; 17:03 UT
Credential Certification: Martin Henze (henze@ice.cat)

Subjects: Optical, Ultra-Violet, Nova, Transient

Referred to by ATel #: 9411

We report optical and UV photometry of the M31 nova candidate M31N 2016-08d (ATel #9388). After the initial discovery with the 0.65-m telescope at Ondrejov, additional observations were obtained with the same instrument. These measurements show that the object is a candidate luminous nova in M31 with an observed peak at R = 15.18 ± 0.06 mag on 2016-08-21.959 UT. Below the text we list the observed optical magnitudes and corresponding uncertainties for the respective dates and filters.

The object was also serendipitously detected in a 600-s Swift/UVOT observation of the nearby recurrent nova M31N 1990-10a (see ATels #9276,#9280) on 2016-08-18.85 UT with uvw1 = 19.0 ± 0.3 mag. An earlier, equally unrelated 800-s Swift/UVOT pointing on 2016-08-16.98 UT showed no convincing detection at the nova position with a 3σ upper limit of uvw1 > 19.6 mag. This observation took place shortly before the first prediscovery detection (ATel #9388) and was obtained for the ongoing Swift M31 centre monitoring (e.g. ATel #9187).

After our optical follow-up suggested a bright peak magnitude, we immediately requested dedicated Swift ToO observations of the object to compare it to other luminous M31 novae like M31N 2009-10b (e.g. ATel #2274) or M31N 2015-09c (e.g. ATels #8109,#8144). A first 2-ks pointing on 2016-08-22.62 UT clearly detected the nova at uvw2 = 19.5 ± 0.2 mag (note the change in UVOT filter). Shortly afterwards, a 1.9-ks observation on 2016-08-24.23 UT found that the magnitude had already dropped to uvw2 = 20.4 ± 0.4 mag. The central wavelengths of the Swift/UVOT filters are: uvw1: 260 nm; uvw2: 193 nm. All Swift magnitudes are in the UVOT photometric (Vega) system (Poole et al. 2008) and have not been corrected for extinction. We will continue the Swift monitoring.

We wish to thank the Swift Team for the rapid scheduling of the ToO observations, in particular N. Gehrels, the duty scientists as well as the science planners.

 
Date [UT]      | Mag   | Err  | Filter 
2016-08-19.945 | 16.67 | 0.09 | R 
2016-08-21.959 | 15.18 | 0.06 | R 
2016-08-22.822 | 15.24 | 0.05 | R 
2016-08-22.836 | 15.65 | 0.06 | V 
2016-08-22.848 | 15.23 | 0.04 | R 
2016-08-24.801 | 15.59 | 0.06 | R 
2016-08-24.812 | 16.08 | 0.06 | V 
2016-08-24.821 | 15.08 | 0.05 | I 
2016-08-24.829 | 15.54 | 0.06 | R 
2016-08-25.121 | 15.78 | 0.07 | R