A comparison of optical and X-ray novae

1979 ◽  
Vol 366 (1726) ◽  
pp. 357-365
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Theoretical Models ◽  
Dwarf Novae ◽  
X Ray ◽  
Classical Novae ◽  
Binary Structure ◽  
Nuclear Burning ◽  
Similarities And Differences

The similarities and differences between optical novae and transient X-ray novae are discussed. Both classes almost certainly require a semi­-detached binary structure. Present theoretical models of classical novae account for the outburst in terms of a nuclear burning runaway in the accreted material on the white dwarf within a semi-detached binary system. In the case of the dwarf novae and the transient X-ray sources, unstable accretion events are the generally accepted model. Mechanisms that could generate unstable accretion events are described.

The Hard X-Ray Spectra of EF Eri and Other CVs

1996 ◽  
Vol 158 ◽  
pp. 205-208
Author(s):  
C. Done ◽  
J. P. Osborne ◽  
A. P. Beardmore
Keyword(s):  
White Dwarf ◽  
Reflection Spectrum ◽  
Strong Shock ◽  
Theoretical Models ◽  
Dwarf Novae ◽  
Iron Line ◽  
X Ray ◽  
Standing Problem

AbstractReflection of the X-ray emission from the surface of the white dwarf should be present in all hard X-ray emitting CV systems. It is clearly identified in the Ginga 2… 20 keV spectra of the polars AM Her and EF Eri, and also in the quiescent spectra of the dwarf novae SS Cyg. The inclusion of the hard reflection spectrum lowers the derived continuum temperature, so resolving a long standing problem of the mismatch of the iron line and continuum properties, and, with more realistic multi-temperature continuua, the derived shock temperatures are close to those expected from theoretical models of a strong shock.

scholarly journals The Intermediate Polars

1983 ◽  
Vol 72 ◽  
pp. 155-172
Author(s):  
Brian Warner
Keyword(s):  
Magnetic Fields ◽  
White Dwarf ◽  
Variable Star ◽  
Theoretical Models ◽  
Cataclysmic Variable ◽  
General Role ◽  
X Ray ◽  
Low Mass ◽  
Intermediate Polars ◽  
X Ray Binaries

Until 1976, cataclysmic variable star research proceeded with few requirements for the inclusion of magnetic fields in theoretical models. Although models for low-mass X-ray binaries stressed the importance of magnetic fields (Lamb et at. 1973) and there was an increasing number of known magnetic single white dwarfs (Angel 1977), and a magnetised white dwarf had been one of the models proposed to explain the rapid oscillations in DQ Her (Herbst et al. 1974, Katz 1975), there was no anticipation of the more general role that magnetic fields now seem destined to play. The two major reviews of the time (Robinson 1976, Warner 1976) scarcely considered the presence of magnetic fields.

scholarly journals Optical Low States of the Supersoft X-Ray Source RXJ0513.9–6951

1997 ◽  
Vol 163 ◽  
pp. 787-787
Author(s):  
K. Reinsch ◽  
A. van Teeseling ◽  
K. Beuermann ◽  
T.M.C. Abbott
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
Mass Transfer Rate ◽  
Central Star ◽  
High Mass ◽  
X Ray ◽  
Total Luminosity ◽  
Nuclear Burning ◽  
Sudden Decrease ◽  
Optical Flux

The transient luminous soft X-ray source RXJ0513.9–6951 (Schaeidt et al., 1993, A&A 270, L9) is a high-mass-transfer binary system (Cowley et al., 1993, ApJ 418, L63; Pakull et al., 1993, A&A 278, L39) with a probable orbital period of 0.76 days (Crampton et al., 1996, ApJ 456, 320). Here, we summarize the results of a quasi-simultaneous optical and X-ray monitoring (see Fig. 1). The sudden decrease of the optical flux, the accompanying reddening, and the turn-on in the soft X-ray band can be quantitatively described by variations in the irradiation of the accretion disk by the hot central star (Reinsch et al., 1996, A&A 309, L11). In this simple model, we consider a white dwarf with nuclear burning of accreted matter (van den Heuvel et al., 1992, A&A 262, 97), surrounded by a flat standard disk. In the optical high state, accretion at near-Eddington rate occurs and the white dwarf photospheric radius must be considerably expanded causing an enhanced illumination of the disk and the secondary. In the optical low state, the photosphere shrinks in response to a temporarily slightly reduced mass-transfer rate. At the same time, the effective temperature increases, and the soft X-ray flux becomes detectable with ROSAT. This model does not depend on the particular cause for the drop in the accretion rate and can describe the optical/ X-ray variability with the total luminosity changing by less than 20 %.

scholarly journals X-ray and Gamma-ray Observations of Pulsars

1981 ◽  
Vol 95 ◽  
pp. 241-250 ◽  
Author(s):  
R. Buccheri
Keyword(s):  
Gamma Ray ◽  
Theoretical Models ◽  
Radio Pulsars ◽  
X Ray ◽  
Special Regard ◽  
Energy Domain ◽  
Similarities And Differences

Measurements of pulsars in the energy domain above ~ 1 keV have provided in the last few years new and interesting results. This paper presents a review of the observational features of PSR 0531+21 and PSR 0833–45 (the Crab and Vela pulsars). Searches for pulsed emission from old radio pulsars in the same energy domain are also reviewed and results assessed. The comparison of the observed features with each other and with the corresponding features observed at lower energies reveals similarities and differences capable to constrain theoretical models with special regard to the geometry of the emission mechanisms.

scholarly journals A Wave Model for Dwarf Novae

1980 ◽  
Vol 58 ◽  
pp. 643-648
Author(s):  
Warren M. Sparks ◽  
G. Siegfried Kutter
Keyword(s):  
Binary System ◽  
White Dwarf ◽  
Wave Model ◽  
Mathematical Representation ◽  
Coherent Oscillation ◽  
Dwarf Novae ◽  
Dwarf Nova ◽  
Nova Outburst

AbstractThe rapid coherent oscillation during a dwarf nova outburst is attributed to an accretion-driven wave going around the white dwarf component of the binary system. The increase and decrease in the period of this oscillation is due to the change in the velocity of the wave as it is first being driven and then damped. Qualitatively, a large number of observations can be explained with such a model. The beginnings of a mathematical representation of this model are developed.

scholarly journals Swift J011511.0-725611: discovery of a rare Be star/white dwarf binary system in the SMC

2021 ◽  
Vol 508 (1) ◽  
pp. 781-788
Author(s):  
J A Kennea ◽  
M J Coe ◽  
P A Evans ◽  
L J Townsend ◽  
Z A Campbell ◽  
...  
Keyword(s):  
Neutron Star ◽  
Binary System ◽  
South African ◽  
White Dwarf ◽  
Compact Object ◽  
Type Ii ◽  
Large Telescope ◽  
X Ray ◽  
Be Star

ABSTRACT We report on the discovery of Swift J011511.0-725611, a rare Be X-ray binary system (BeXRB) with a white dwarf (WD) compact object, in the Small Magellanic Cloud (SMC) by S-CUBED, a weekly X-ray/UV survey of the SMC by the Neil Gehrels Swift Observatory. Observations show an approximately 3 month outburst from Swift J011511.0-725611, the first detected by S-CUBED since it began in 2016 June. Swift J011511.0-725611 shows supersoft X-ray emission, indicative of a WD compact object, which is further strengthened by the presence of an 0.871 keV edge, commonly attributed to O viii K-edge in the WD atmosphere. Spectroscopy by South African Large Telescope confirms the Be nature of the companion star, and long term light curve by OGLE finds both the signature of a circumstellar disc in the system at outburst time, and the presence of a 17.4 day periodicity, likely the orbital period of the system. Swift J011511.0-725611 is suggested to be undergoing a Type-II outburst, similar to the previously reported SMC Be white dwarf binary (BeWD), Swift J004427.3-734801. It is likely that the rarity of known BeWD is in part due to the difficulty in detecting such outbursts due to both their rarity, and their relative faintness compared to outbursts in Neutron Star BeXRBs.

scholarly journals Classical Nova Evolution: Clues from Soft X-Ray Emission

1996 ◽  
Vol 158 ◽  
pp. 281-287
Author(s):  
James MacDonald
Keyword(s):  
Effective Temperature ◽  
White Dwarf ◽  
Mass Change ◽  
Stellar Winds ◽  
X Ray ◽  
Classical Novae ◽  
Bolometric Luminosity ◽  
Classical Nova ◽  
Multi Wavelength ◽  
Nova Outbursts

AbstractMulti-wavelength observations have shown that, after optical decline, the stellar remnants of classical nova outbursts evolve at constant, near-Eddington, bolometric luminosity to high effective temperature (> 2 105 K), before turning off. Here we briefly review the observations of classical novae in this phase of evolution, and discuss what the soft X-ray observations tell us about the mass of the underlying white dwarf and the rate of mass change due to stellar winds and accretion from the stellar companion.

Exosat Observations of X-Rays from Classical Novae during Outburst Stage

1987 ◽  
Vol 93 ◽  
pp. 279-279
Author(s):  
H. Ögelman ◽  
J. Krautter ◽  
K. Beuermann
Keyword(s):  
White Dwarf ◽  
Central Star ◽  
Maximum Temperature ◽  
Infrared Range ◽  
First Year ◽  
X Rays ◽  
Core Mass ◽  
X Ray ◽  
Classical Novae ◽  
Bolometric Luminosity

AbstractThe initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime of EXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984 # 1 (PW Vul), and two observations of Nova Vulpeculae 1984 # 2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to ~ 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is ~ 2 to 3 years, which leads to the conclusion that the burned envelope mass Mburn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9 M⊙, core luminosity of ~ 2 × 104L⊙, and envelope mass of 10−6M⊙, can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have ≥ 1.1 M⊙ core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind with Ṁ ≤ 5 × 10−7M⊙yr−1 appears to be necessary. The few observations of Nova Vulpeculae 1984 # 1 and Nova Vulpeculae 1984 # 2 , during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.

scholarly journals Inner Disk Structure of Dwarf Novae in the Light of X-Ray Observations

2015 ◽  
Vol 2 (1) ◽  
pp. 116-122 ◽  
Author(s):  
S. Balman
Keyword(s):  
White Dwarf ◽  
Spectral Characteristics ◽  
Time Variability ◽  
Time Lags ◽  
X Rays ◽  
Dwarf Novae ◽  
Disk Radius ◽  
X Ray ◽  
Disk Structure ◽  
Band Limited

Diversity of the X-ray observations of dwarf nova are still not fully understood. I review the X-ray spectral characteristics of dwarf novae during the quiescence in general explained by cooling flow models and the outburst spectra that show hard X-ray emission dominantly with few sources that reveal soft X-ray/EUV blackbody emission. The nature of aperiodic time variability of brightness of dwarf novae shows band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break (1-6 mHz) indicates inner disk truncation of the optically thick disk with a range of radii (3.0-10.0)×109 cm. The RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence reveal that the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. A preliminary analysis of SU UMa indicates a similar behaviour. In addition, I find that the outburst spectra of WZ Sge shows two component spectrum of only hard X-ray emission, one of which may be fitted with a power law suggesting thermal Comptonization occuring in the system. Cross-correlations between the simultaneous UV and X-ray light curves (XMM −Newton) of five DNe in quiescence show time lags in the X-rays of 96-181 sec consistent with travel time of matter from a truncated inner disk to the white dwarf surface. All this suggests that dwarf novae and other plausible nonmagnetic systems have truncated accretion disks indicating that the disks may be partially evaporated and the accretion may occur through hot (coronal) flows in the disk.

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