Multiwavelength modeling the SED of supersoft X-ray sources III. RS Ophiuchi: The supersoft X-ray phase and beyond

Abstract

-Multiwavelength model SEDs of the nova RS Oph from X-rays to mid-IR were performed. -During the supersoft source phase its luminosity was highly super-Eddington. -It was sustained by a high accretion rate from a disk, followed by jets. -During quiescence the SED satisfied radiation produced by a large accretion disk. -The high accretion rate could be realized throughout a focused wind of the giant. AbstractI modelled the 14Å-37 µm SED of the recurrent symbiotic nova RS Oph during its supersoft source (SSS) phase and the following quiescent phase. During the SSS phase, the model SEDs revealed the presence of a strong stellar and nebular component of radiation in the spectrum. The former was emitted by the burning WD at highly super-Eddington rate, while the latter represented a fraction of its radiation reprocessed by the thermal nebula. During the transition phase, both the components were decreasing and during quiescence the SED satisfied radiation produced by a large, optically thick disk (R disk > 10 R⊙). The super-Eddington luminosity of the burning WD during the SSS phase was independently justified by the high quantity of the nebular emission. The emitting material surrounded the burning WD, and its mass was (1.6 ± 0.5) × 10 −4 (d/1.6 kpc) 5/2 M⊙. The helium ash, deposited on the WD surface during the whole burning period, was around of 8 × 10 −6 (d/1.6 kpc) 2 M⊙, which yields an average growing rate of the WD mass,ṀWD ∼ 4 × 10 −7 (d/1.6 kpc) 2 M⊙ yr −1 . The mass accreted by the WD between outbursts, macc ∼ 1.26 × 10 −5 M⊙, constrains the average accretion rate,Ṁacc ∼ 6.3 × 10 −7 M⊙ yr −1 . During quiescence, the accretion rate from the model SED of ∼ 2.3 × 10 −7 M⊙ yr −1 requires a super-Eddington accretion from the disk at ∼ 3.6 × 10 −5 M⊙ yr −1 during the outburst. Such a high accretion can be responsible for the super-Eddington luminosity during the whole burning phase. Simultaneous presence of jets supports this scenario. If the wind from the giant is not sufficient to feed the WD at the required rate, the accretion can be realized from the disk-like reservoir of material around the WD. In this case the time between outbursts will extend, with the next explosion beyond 2027. In the opposite case, the wind from the giant has to be focused to the orbital plane to sustain the high accretion rate at a few ×10 −7 M⊙ yr −1 . Then the next explosion can occur even prior to 2027.

Optical flickering of the recurrent nova RS Ophiuchi: amplitude–flux relation☆

“…The grids of colours for cool stars (Houdashelt, Bell, Sweigartet 2000) Skopal (2015) modelled the spectral energy distribution of RS Oph adopting V ∼ 12.0 for the red giant. Using decomposition of the spectrum of RS Oph in quiescence, Kelly et al (2014) estimated that the giant star should be 0.65 mag fainter in V than the total magnitude of the binary system, which they suppose to be ∼ 11.5.…”

The applicability of the wind compression model

“…They found that the wind compression model may have relevance for slow novae, which tend to maintain winds with low terminal speeds of a few hundred km s −1 throughout their outbursts. Recently, the observed evolution of the biconical ionization structure of fast novae V339 Del (v ∞ ∼ 2700 km s −1 ) and RS Oph (v ∞ ∼ 4000 km s −1 ) was also possible to interpret qualitatively in terms of the WCZ model (see Skopal 2014). However, a theoretical application of the WCZ model to the fast nova mass outflow is needed to test this interpretation.…”

Rise and fall of silicate dust in RS Ophiuchi following the 2006 eruption

“…The contribution from free-free emission is already relatively small by that time. We use the Skopal (2015) results for the SED of the hot component, adopting a 25,000 K blackbody with a luminosity of L = 370 L⊙. We use a model spectrum for the red giant companion, fitted to near infrared spectra from the post outburst minimum (Rushton et al 2010;Pavlenko et al 2016).…”

“…The quiescent fluxes F λ (total) were approximated by computing the contributions from the three principal components: F λ (total) = F λ (RG) + F λ (AD) + F λ (BL), where F λ (RG) is the flux from the red giant, F λ (AD) is an optically thick accretion disk, which radiates locally as a blackbody and F λ (BL) is the contribution from the boundary layer (Skopal 2015;Pavlenko et al 2016). The luminosities and characteristic temperatures are from Skopal (2015).…”

“…For the mass-loss rate, the luminosity of the central source is used to scale the programme output from the value of 10 4 L⊙ assumed by Dusty (Ivezić, Nenkova & Elitzur 1999). We use the values from Skopal (2015) for the central source (1.0 × 10 3 L⊙ for 2006 and 1.7 × 10 3 L⊙ for 2007-2009) at an assumed distance to RS Oph of 1.6 kpc (Hjellming & van Gorkom 1986). The mass-loss rate scales with distance as d 3/2 (Ivezić, Nenkova & Elitzur 1999).…”