Abstract
ABSTRACT The recurrent symbiotic nova V745 Sco exploded on 2014 February 6 and was observed on February 22 and 23 by the Chandra X-ray Observatory Transmission Grating Spectrometers. By that time the supersoft source phase had already ended, and Chandra spectra are consistent with emission from a hot, shock-heated circumstellar medium with temperatures exceeding 107 K. X-ray line profiles are more sharply peaked than expected for a spherically symmetric blast wave, with a full width at zero intensity of approximately 2400 km s−1, an FWHM of 1200 ± 30 km s−1, and an average net blueshift of 165 ± 10 km s−1. The red wings of lines are increasingly absorbed toward longer wavelengths by material within the remnant. We conclude that the blast wave was sculpted by an aspherical circumstellar medium in which an equatorial density enhancement plays a role, as in earlier symbiotic nova explosions. Expansion of the dominant X-ray-emitting material is aligned close to the plane of the sky and is most consistent with an orbit seen close to face-on. Comparison of an analytical blast wave model with the X-ray spectra, Swift observations, and near-infrared line widths indicates that the explosion energy was approximately 1043 erg and confirms an ejected mass of approximately 10−7 M ⊙. The total mass lost is an order of magnitude lower than the accreted mass required to have initiated the explosion, indicating that the white dwarf is gaining mass and is a Type Ia supernova progenitor candidate.
Highlights
V745 Sco is a member of the exclusive class of cataclysmic variables known as recurrent symbiotic novae
Recurrent novae (RNe) are cases of generally more massive white dwarfs with accretion rates approaching that required for steady surface nuclear burning that engender outbursts at quasi-regular intervals of only a few years
The full width at zero intensity (FWZI) of approximately 1200 km s−1 is to be compared with the smaller net blueshift of 165 km s−1; the latter figure is likely slightly biased toward larger blueshift by the differential absorption discussed in Section 4.3, we point to Figure 4 as an illustration that this does seem appropriate for the relatively unabsorbed Si and Mg H-like and He-like resonance lines
Summary
V745 Sco is a member of the exclusive class of cataclysmic variables known as recurrent symbiotic novae. Symbiotic novae are close binaries in which a white dwarf orbits within the wind or extended atmosphere of an evolved companion. A bipolar morphology was indicated by both radio and optical imaging of the 2006 RS Oph outburst (O’Brien et al 2006; Bode et al 2007; Sokoloski et al 2008; Ribeiro et al 2009), while Drake et al (2009) found the signature of a collimated blast in high-resolution Chandra X-ray spectra that provided a direct probe of the shock-heated plasma. The Chandra high-resolution X-ray spectrometers were deployed to observe the 2014 V745 Sco explosion and investigate the nature of the blast wave and SSS. We analyze the unique constraints on the blast wave conditions and geometry afforded by the Chandra data, complemented by monitoring observations made by Swift and near-infrared Paschen line widths culled from the literature
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