A Light-curve Analysis of the X-Ray Flash First Observed in Classical Novae

Kato, Mariko; Saio, Hideyuki; Hachisu, Izumi

doi:10.3847/2041-8213/ac85c1

Cited by 10 publications

(13 citation statements)

References 19 publications

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“…From the theoretical point of view, many numerical calculations have been presented from the early thermonuclear runaway to the extended phase of nova outbursts (e.g., Prialnik & Kovetz 1992, 1995Epelstain et al 2007;Starrfield et al 2009;Denissenkov et al 2013;Chen et al 2019;Kato et al 2022aKato et al , 2022b. These works clarified that mass ejection is continuous, and no multiple distinct mass ejections occur.…”

Section: Introductionmentioning

confidence: 99%

“…A huge amount of nuclear energy is generated, which is once absorbed by the layer around nuclear burning region and then will be released in a later phase with a long timescale. During the nova outburst, the white dwarf (WD) envelope quickly expands to a giant size, but no shock arises below the photosphere (e.g., Denissenkov et al 2013;Kato et al 2022aKato et al , 2022b. Thus, the statement "no shock arises during/after thermonuclear runaway" is the current understanding in nova theory.…”

Section: Introductionmentioning

confidence: 99%

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A Strong Shock During a Nova Outburst: An Origin of Multiple Velocity Systems in Optical Spectra and of High-energy Emissions

Hachisu¹,

Kato

2022

ApJ

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We propose a theoretical explanation of absorption/emission line systems in classical novae based on a fully self-consistent nova explosion model. We found that a reverse shock is formed far outside the photosphere (≳1013 cm) because later-ejected mass with a faster velocity collides with earlier-ejected matter. Optically thick winds blow continuously at a rate of ∼10−4 M ☉ yr−1 near the optical maximum, but its velocity decreases toward the optical maximum and increases afterward, so that the shock arises only after the optical maximum. The nova ejecta is divided by the shock into three parts, the outermost expanding gas (earliest wind before maximum), shocked shell, and inner fast wind, which respectively contribute to pre-maximum, principal, and diffuse-enhanced absorption/emission line systems. A large part of nova ejecta is eventually confined to the shocked shell. The appearance of the principal system is consistent with the emergence of a shock. This shock is strong enough to explain thermal hard X-ray emissions. The shocked layer has a high temperature of kT sh ∼ 1 keV × ( ( v wind − v shock ) / 1000 km s − 1 ) 2 = 1 keV × ( ( v d − v p ) / 1000 km s − 1 ) 2 , where v d − v p is the velocity difference between the diffuse-enhanced (v d) and principal (v p) systems. We compare a 1.3 M ☉ white dwarf model with the observational properties of the GeV gamma-ray detected classical nova V5856 Sgr (ASASSN-16ma) and discuss what kind of novae can produce GeV gamma-ray emissions.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Strong Shock During a Nova Outburst: An Origin of Multiple Velocity Systems in Optical Spectra and of High-energy Emissions

Hachisu¹,

Kato

2022

ApJ

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“…YZ Ret was classified as a nova-like VY Scl variable by these fadings. The mass-accretion rate onto the WD is ( M acc   2-3 ) × 10 −9 M ☉ yr −1 (Kato et al 2022b), because dwarf nova outbursts are suppressed in a nova-like VY Scl star (e.g., Osaki 1996). Schaefer (2022) reported the pre-eruption orbital period of P orb = 0.1324539 ± 0.0000098 days (=3.179 hr) based on TESS optical photometry.…”

Section: Pre-nova Observationsmentioning

confidence: 99%

“…The classical nova YZ Ret went into outburst in 2020. It is characterized by the first detection of an X-ray flash in classical novae (Kato et al 2022b;König et al 2022). Gigaelectronvolt gamma-rays were observed during the 10 days just after the optical maximum, which indicates formation of a strong shock (Sokolovsky et al 2022).…”

Section: Introductionmentioning

confidence: 99%

A Multiwavelength Light-curve Analysis of the Classical Nova YZ Ret: An Extension of the Universal Decline Law to the Nebular Phase

Hachisu,

Kato

2023

ApJ

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YZ Ret is the first X-ray flash detected classical nova, and is also observed in optical, X-ray, and gamma-ray. We propose a comprehensive model that explains the observational properties. The white dwarf mass is determined to be ∼1.33 M ☉, which reproduces the multiwavelength light curves of YZ Ret, from optical, X-ray, to gamma-ray. We show that a shock is naturally generated far outside the photosphere because winds collide with themselves. The derived lifetime of the shock explains some of the temporal variations of emission lines. The shocked shell significantly contributes to the optical flux in the nebular phase. The decline trend of shell emission in the nebular phase is close to ∝t −1.75 and the same as the universal decline law of classical novae, where t is the time from the outburst.

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“…(i) 'fireball' phase -a bright soft (< 0.1 keV) thermal X-ray flash seen hours before the optical rise (König et al 2022;Kato et al 2022);…”

Section: Introductionmentioning

confidence: 99%

The multi-wavelength view of shocks in the fastest nova V1674 Her

Sokolovsky,

Johnson,

Buson

et al. 2023

Preprint

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Classical novae are shock-powered multi-wavelength transients triggered by a thermonuclear runaway on an accreting white dwarf. V1674 Her is the fastest nova ever recorded (time to declined by two magnitudes is 2 = 1.1 d) that challenges our understanding of shock formation in novae. We investigate the physical mechanisms behind nova emission from GeV -rays to cm-band radio using coordinated Fermi-LAT, NuSTAR, Swift and VLA observations supported by optical photometry. Fermi-LAT detected short-lived (18 h) 0.1-100 GeV emission from V1674 Her that appeared 6 h after the eruption began; this was at a level of (1.6 ± 0.4) × 10 −6 photons cm −2 s −1 . Eleven days later, simultaneous NuSTAR and Swift X-ray observations revealed optically thin thermal plasma shock-heated to k shock = 4 keV. The lack of a detectable 6.7 keV Fe K emission suggests supersolar CNO abundances. The radio emission from V1674 Her was consistent with thermal emission at early times and synchrotron at late times. The radio spectrum steeply rising with frequency may be a result of either free-free absorption of synchrotron and thermal emission by unshocked outer regions of the nova shell or the Razin-Tsytovich effect attenuating synchrotron emission in dense plasma. The development of the shock inside the ejecta is unaffected by the extraordinarily rapid evolution and the intermediate polar host of this nova.

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A Light-curve Analysis of the X-Ray Flash First Observed in Classical Novae

Cited by 10 publications

References 19 publications

A Strong Shock During a Nova Outburst: An Origin of Multiple Velocity Systems in Optical Spectra and of High-energy Emissions

A Strong Shock During a Nova Outburst: An Origin of Multiple Velocity Systems in Optical Spectra and of High-energy Emissions

A Multiwavelength Light-curve Analysis of the Classical Nova YZ Ret: An Extension of the Universal Decline Law to the Nebular Phase

The multi-wavelength view of shocks in the fastest nova V1674 Her

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