Swift observations of SMC nova ASASSN-20ni
ATel #14137; N Paul M Kuin (MSSL/UCL), Steven N Shore (Universitá di Pisa ), Kim L Page (Leicester U)
on 31 Oct 2020; 18:44 UT
Credential Certification: Paul Kuin (npkuin@gmail.com)
Subjects: Ultra-Violet, Nova
The classical nova ASASSN-20ni discovery was reported by Way et al. in ATEL #14122. Spectroscopic follow up by Aydi et al (ATEL #14123) confirms the nova identification.
It is probably associated with the SMC. Way et al. reported an ASAS-SN pre-eruption upper limit of g>16.5.
Since 2016 the Swift mission has been monitoring the SMC several times a year with the X-ray Telescope and in the uvw1 filter with the UV-Optical Telescope. No source is visible in the individual or summed images with a pre-eruption upper limit of uvw1=20.9 (AB) mag at 260nm.
After the discovery of the eruption, on October 28.55 this was uvw1 = 13.91 +/- 0.02 (AB) mag, and rising; an increase so far of more than 7 magnitudes. No corresponding X-ray source was detected with the Swift X-ray Telescope, to a 3 sigma upper limit of 0.006 count s^-1.
We obtained an initial spectrum with the UV grism on October 28.55, and two more on October 29.75 and 29.95. These show a very strong jump of more than a factor two in flux starting at 366nm, with a weak UV spectrum at shorter wavelengths. The uvw1 filter is centered on 260nm, and therefore these magnitudes are fainter than in the optical.
The spectra show no lines of the H Balmer series, although there are a number of absorption features that change from spectrum to spectrum. They are similar to, for example, the very early December 13 1934 spectra of the eruption of DQ Her in the review by Arthur Beer (1974, Vistas in Astronomy, vol. 16, Issue 1, pp.179-260).
Swift will continue to monitor the nova.
