The 2019 eruption of recurrent nova V3890 Sgr: observations by Swift, NICER and SMARTS

TL;DR

This paper presents detailed multi-wavelength observations of the 2019 eruption of recurrent nova V3890 Sgr, revealing shock emission, super-soft X-ray phase, ejecta-wind interaction, and short-term oscillations, advancing understanding of nova outburst mechanisms.

Contribution

It provides the first comprehensive multi-instrument observational analysis of V3890 Sgr's 2019 eruption, highlighting timing, spectral features, and variability that inform white dwarf mass and eruption dynamics.

Findings

Super-soft X-ray phase begins around day 8.5 and ends by day 26.

White dwarf mass estimated at approximately 1.3 solar masses.

Detection of an 83-second quasi-periodic oscillation during the super-soft phase.

Abstract

V3890 Sgr is a recurrent nova which has been seen in outburst three times so far, with the most recent eruption occurring on 2019 August 27 UT. This latest outburst was followed in detail by the Neil Gehrels Swift Observatory, from less than a day after the eruption until the nova entered the Sun observing constraint, with a small number of additional observations after the constraint ended. The X-ray light-curve shows initial hard shock emission, followed by an early start of the super-soft source phase around day 8.5, with the soft emission ceasing by day 26. Together with the peak blackbody temperature of the super-soft spectrum being ~100 eV, these timings suggest the white dwarf mass to be high, ~1.3 M_sun. The UV photometric light-curve decays monotonically, with the decay rate changing a number of times, approximately simultaneously with variations in the X-ray emission. The UV grism spectra show both line and continuum emission, with emission lines of N, C, Mg and O being notable. These UV spectra are best dereddened using an SMC extinction law. Optical spectra from SMARTS show evidence of interaction between the nova ejecta and wind from the donor star, as well as the extended atmosphere of the red giant being flash-ionized by the super-soft X-ray photons. Data from NICER reveal a transient 83 s quasi-periodic oscillation, with a modulation amplitude of 5 per cent, adding to the sample of novae which show such short variabilities during their super-soft phase.