Getting to know classical novae with Swift

Abstract

Novae have been reported as transients for more than two thousand years. Their bright optical outbursts are the result of explosive nuclear burning of gas accreted from a binary companion onto a white dwarf. Novae containing a white dwarf close to the Chandrasekhar mass limit and accreting at a high rate are potentially the unknown progenitors of the type Ia supernovae used to measure the acceleration of the Universe. Swift X--ray observations have radically transformed our view of novae by providing dense monitoring throughout the outburst, revealing new phenomena in the super--soft X--rays from the still--burning white dwarf such as early extreme variability and half-- to one--minute timescale quasi--periodic oscillations. The distinct evolution of this emission from the harder X--ray emission due to ejecta shocks has been clearly delineated. Soft X--ray observations allow the mass of the white dwarf, the mass burned and the mass ejected to be estimated. In combination with observations at other wavelengths, including the high spectral resolution observations of the large X--ray observatories, high resolution optical and radio imaging, radio monitoring, optical spectroscopy, and the detection of GeV gamma--ray emission from recent novae, models of the explosion have been tested and developed. I review nine novae for which Swift has made a significant impact; these have shown the signature of the components in the interacting binary system in addition to the white dwarf: the re--formed accretion disk, the companion star and its stellar wind.

X-RAY FLASHES IN RECURRENT NOVAE: M31N 2008-12a AND THE IMPLICATIONS OF THE SWIFT NONDETECTION

“…Hachisu & Kato 2006, 2010, 2015, 2016aOsborne 2015;Schwarz et al 2011, and references therein). The evolution of novae has been modeled by the optically thick wind theory (Kato & Hachisu 1994), and their theoretical light curves for D-E-F have successfully reproduced the observed light curves including NIR, optical, UV, and supersoft X-rays.…”

“…From point E to F, the duration of the supersoft X-ray phase is theoretically reproduced. Detailed comparison with theory and observation enables us to determine/constrain the nova parameters such as the WD mass, distance, and extinction, in many novae , 2015, 2016a. Thus, the characteristic properties of a nova from D to F have been well understood in both observational and theoretical terms.…”

Novae as Tevatrons: prospects for CTA and IceCube

“…Williams & Mason 2010), hard X-ray emission starting weeks to years after the outburst (e.g. Mukai et al 2008;Osborne 2015), and an early sharp maximum in the radio light curve on timescales of months, in ex-E-mail: bmetzger@phys.columbia.edu cess of that expected from freely-expanding photo-ionized ejecta (e.g., Chomiuk et al 2014;Weston et al 2015).…”

M31N 2008-12a—THE REMARKABLE RECURRENT NOVA IN M31: PANCHROMATIC OBSERVATIONS OF THE 2015 ERUPTION

“…Following the TNR the nuclear fusion enters a period of short-lived, approximately steady-state burning until the accreted fuel is exhausted, partly because it has been ejected and partly because what remained has been burned to helium (Prialnik et al 1978). As the optical depth of the expanding ejecta becomes progressively smaller, the pseudo-photosphere begins to recede back toward the WD surface, subsequently shifting the peak of the emission back to higher energies until ultimately a supersoft X-ray source (SSS) may emerge (see, for example, Hachisu & Kato 2006;Krautter 2008;Osborne 2015). The "turn-off" of the SSS indicates the end of the nuclear burning, after which the system eventually returns to its quiescent state.…”