Chemical and Physical Parameters From X-Ray High-Resolution Spectra of the Galactic Nova V959 Mon

Abstract

Two observations of V959 Mon, done using the Chandra X-ray gratings during the late outburst phases (2012 September and December), offer extraordinary insight into the physics and chemistry of this Galactic ONe nova. The X-ray flux was 1.7 × 10 −11 erg cm −2 s −1 and 8.6 × 10 −12 erg cm −2 s −1 , respectively at the two epochs. The first result, coupled with electron density diagnostics and compared with published optical and ultraviolet observations, indicates that most likely in 2012 September the X-rays originated from a very small fraction of the ejecta, concentrated in very dense clumps. We obtained a fairly good fit to the September spectrum with a model of plasma in collisional ionization equilibrium (CIE) with two components; one at a temperature of 0.78 keV, associated with flat-topped and asymmetrical emission lines, blueshifted by 710-930 km s −1 ; the other at a temperature of 4.5 keV, mostly contributing to the high-energy continuum. However, we cannot rule out a range of plasma temperatures between these two extremes; we also modeled the spectrum as a static cooling flow, but the available models and the data quality are not adequate yet to differentiate between the two-component fit and a smoothly varying temperature structure. In December, the central white dwarf (WD) became visible in X-rays. We estimate an effective temperature of 680,000 K, consistent with a WD mass ≥1.1 M . The WD flux is modulated with the orbital period, indicating high inclination, and two quasi-periodic modulations with hour timescales were also observed. No hot plasma component with temperature above 0.5 keV was observed in December, and the blueshifted component cooled to kT 0.45 keV. Additionally, new emission lines due to a much cooler plasma appeared, which were not observed two months earlier. We estimate abundances and yields of elements in the nova wind that cannot be measured in the optical spectra and confirm the high Ne abundance previously derived for this nova. We also find high abundance of Al, 230 times the solar value, consistently with the prediction that ONe novae contribute to at least 1/3rd of the Galactic yield of 26 Al.

Chandra High Energy Transmission Gratings Spectra of V3890 Sgr

“…compare the fluxes with those obtained by Peretz et al (2016) for V959 Mon, known as a nova on an ONe WD. We find that the ratio of the flux of the lines Al, Mg, and Ne (elements expected to be enhanced in novae on ONe WDs), relative to the flux of the Si lines, are much lower than in V959 Mon, despite plasma temperatures of about the same value.…”

The Supersoft X-Ray Transient ASASSN-16oh as a Thermonuclear Runaway without Mass Ejection

“…We examined the Chandra zero-order light curves measured with the HRC-S camera in the exposure described in Section 2, Maccarone et al (2019), because thermonuclear burning SSS seem to be associated either with phenomena of short pulsations lasting around a minute or less (see Ness et al 2015, and references therein), or with longer periodicities of the order of half an hour. For the latter, examples are V1494 Aql (Drake et al 2003), V4743 Sgr (Leibowitz et al 2006;Zemko et al 2016;Dobrotka & Ness 2017), V2491 Cyg (Ness et al 2011;Zemko et al 2015), V959 Mon (Peretz et al 2016). These periodic modulations over tens of minutes have been attributed to the WD spin for V4743 Sgr and V2491 Cyg.…”

What We Learn from the X-Ray Grating Spectra of Nova SMC 2016

“…In most novae, the peak luminosity of this emission from the shell is 10 34 erg s −1 (see e.g. Orio et al 1996Orio et al , 2001Peretz et al 2016). In symbiotic novae, in which the secondary is a red giant, the impact of the ejecta with the giant wind produces thermal X-ray emission with a peak luminosity even as high as 10 36 erg s −1 (Nelson et al 2008;Ness et al 2007).…”