The expanding fireball of Nova Delphini 2013

Abstract

A classical nova occurs when material accreting onto the surface of a white dwarf in a close binary system ignites in a thermonuclear runaway. Complex structures observed in the ejecta at late stages could result from interactions with the companion during the common-envelope phase. Alternatively, the explosion could be intrinsically bipolar, resulting from a localized ignition on the surface of the white dwarf or as a consequence of rotational distortion. Studying the structure of novae during the earliest phases is challenging because of the high spatial resolution needed to measure their small sizes. Here we report near-infrared interferometric measurements of the angular size of Nova Delphini 2013, starting one day after the explosion and continuing with extensive time coverage during the first 43 days. Changes in the apparent expansion rate can be explained by an explosion model consisting of an optically thick core surrounded by a diffuse envelope. The optical depth of the ejected material changes as it expands. We detect an ellipticity in the light distribution, suggesting a prolate or bipolar structure that develops as early as the second day. Combining the angular expansion rate with radial velocity measurements, we derive a geometric distance to the nova of 4.54 ± 0.59 kiloparsecs from the Sun.

Novae as Tevatrons: prospects for CTA and IceCube

“…One physical picture, consistent with both optical (e.g., Schaefer et al 2014) and radio imaging (e.g., Chomiuk et al 2014), and the evolution of optical spectral lines (e.g., Ribeiro et al 2013;Shore et al 2013), is that the thermonuclear runaway is first accompanied by a slow ejection of mass with a toroidal geometry, the shape of which may be influenced by the binary companion (e.g., Livio et al 1990;Lloyd et al 1997). This slow outflow is then followed by a second discrete ejection or continuous wind (e.g., Bath & Shaviv 1976) with a higher velocity and more spherical geometry.…”

Shock-powered radio emission from V5589 Sagittarii (Nova Sgr 2012 #1)

“…It remains to be seen how the upper limit on the γ-ray flux from V5589 Sgr compares with the detections of the four later Fermi-detected novae, all of which were observed in pointed mode with fluxes as faint as 2-3×10 −7 photons cm −2 s −1 . When the distances of 1.4 ± 0.04 kpc for V959 Mon (Linford et al 2015), > 6.5 kpc for V1324 Sco , and 4.5 ± 0.6 kpc for V339 Del (Schaefer et al 2014) are taken into account, V5589 Sgr appears to have been less luminous in the γ-rays than at least V1324 Sco and V339 Del. Since V339 Del is thought to have a low inclination and therefore to be viewed pole on (Schaefer et al 2014), viewing angle could play a role in setting the γ-ray luminosity.…”

“…When the distances of 1.4 ± 0.04 kpc for V959 Mon (Linford et al 2015), > 6.5 kpc for V1324 Sco , and 4.5 ± 0.6 kpc for V339 Del (Schaefer et al 2014) are taken into account, V5589 Sgr appears to have been less luminous in the γ-rays than at least V1324 Sco and V339 Del. Since V339 Del is thought to have a low inclination and therefore to be viewed pole on (Schaefer et al 2014), viewing angle could play a role in setting the γ-ray luminosity. Alternatively, whereas Metzger et al (2015) argued that most relativistic protons in V1324 Sco and V339 Del were trapped and collided with proton targets to produce γ-rays, the low X-ray absorbing column for V5589 Sgr suggests that the ejecta mass might have been too low and/or the expansion speeds too high for this to have been the case for V5589 Sgr.…”

Rise and fall of the dust shell of the classical nova V339 Delphini

“…These derived lower limits should be smaller than the actual n e values because τ (Br γ ) can be considerably >1. An additional caveat in this analysis is the intrinsic assumption of spherical geometry for the ejecta (Slavin, O'Brien & Dunlop 1995), since a bipolar morphology appears more appropriate for V339 Del (see also Schaefer et al 2014;Shore et al 2016).…”

“…Munari et al (2013a) determined the interstellar reddening to V339 Del to be E(B − V) = 0.18, which we adopt here. Schaefer et al (2014) obtained near-IR interferometry of V339 Del, measuring its angular size within a day of the eruption. They observed the expansion of the remnant and, in conjunction with an assumed ejection velocity of 613 ± 79 km s −1 , deduced a distance of 4.54 ± 0.59 kpc for the nova.…”