scholarly journals Spatial distribution of the X-ray-emitting plasma of U Geminorum in quiescence and outburst

2020 ◽  
Author(s):  
Mai Takeo ◽  
Takayuki Hayashi ◽  
Manabu Ishida ◽  
Nozomi Nakaniwa ◽  
Yoshitomo Maeda
Keyword(s):  
Boundary Layer ◽  
White Dwarf ◽  
Flow Model ◽  
Accretion Rate ◽  
Maximum Temperature ◽  
Significant Information ◽  
X Ray ◽  
Cooling Flow ◽  
Hot Plasma ◽  
Data Coverage

Abstract We present our analysis of the Suzaku data of U Geminorum (U Gem) from 2012 both in quiescence and outburst. Unlike SS Cygni (SS Cyg), the hard X-ray flux of U Gem is known to increase at times of optical outburst. A sophisticated spectral model and reliable distance estimate now reveal that this can be attributed to the fact that the mass accretion rate onto the white dwarf (WD) does not exceed the critical rate that causes the optically thin to thick transition of the boundary layer. From comparison of the X-ray and optical light curves, the X-ray outburst peak seems to be retarded by 2.1 ± 0.5 d, although there remains uncertainty in the X-ray peak identification, due to short data coverage. The larger delay than SS Cyg (0.9–1.4 d) also supports the lower accretion rate in U Gem. A fluorescent iron 6.4 keV emission line bears significant information about the geometry of the X-ray-emitting hot plasma and the accretion disk (AD) that reflects the hard X-ray emission. Our reflection simulation has shown that the optically thick AD is truncated at a distance of 1.20–1.25 times the white dwarf radius (RWD) in quiescence, and the accreting matter in the disk turns into the optically thin hard-X-ray-emitting plasma at this radius. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface, although disk truncation can take place in the region of <1.012 RWD. From the profile of the 6.4 keV line, we have also discovered that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the boundary layer at the disk truncation radius. This is consistent with the fact that the hard X-ray spectra of dwarf novae, in general, can be well represented with the cooling flow model.

scholarly journals Spatial distribution of the X-ray-emitting plasma of SS Cygni in quiescence and outburst

2021 ◽  
Author(s):  
Mai Takeo ◽  
Takayuki Hayashi ◽  
Manabu Ishida ◽  
Nozomi Nakaniwa ◽  
Yoshitomo Maeda
Keyword(s):  
White Dwarf ◽  
Radial Distance ◽  
Radial Position ◽  
Maximum Temperature ◽  
Significant Information ◽  
X Ray ◽  
Upper Limit ◽  
Hot Plasma ◽  
Disk Plane ◽  
Plasma Torus

Abstract We present our analysis of the Suzaku data of SS Cygni (SS Cyg) from 2005 both in quiescence and outburst. A fluorescent iron Kα line bears significant information about the geometry of an X-ray-emitting hot plasma and a cold reflector, such as the surfaces of the white dwarf (WD) and the accretion disk (AD). Our reflection simulation has revealed that the X-ray-emitting hot plasma is located either very close to the WD surface in the boundary layer (BL), with an upper limit radial position of <1.004 times the white dwarf radius (RWD), or near the entrance of the BL where the optically thick AD is truncated at a distance of 1.14–1.27 RWD for the assumed WD mass of 1.19 M⊙ in quiescence. In the latter configuration, the plasma torus is located just above the inner edge of the AD. The result suggests that the accreting matter is heated up close to the maximum temperature immediately after the matter enters the BL. The matter probably expands precipitously at the entrance of the BL and leaves the disk plane to reach a height comparable to the radial distance of the plasma torus from the center of the WD. In outburst, on the other hand, our spectral analysis favors the picture that the optically thick disk reaches the WD surface. In addition, the plasma distributes above the disk like coronae, as suggested by a previous study, and the 90% upper limit of the coronae radial position is 1.2 RWD.

scholarly journals ROSAT observations of non-magnetic CVs

1996 ◽  
Vol 158 ◽  
pp. 273-276 ◽  
Author(s):  
A. van Teeseling ◽  
F. Verbunt ◽  
K. Beuermann
Keyword(s):  
Boundary Layer ◽  
Accretion Disk ◽  
White Dwarf ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
Rotation Velocity ◽  
X Rays ◽  
X Ray ◽  
Orbital Modulation ◽  
Magnetic Cataclysmic Variables

In non-magnetic cataclysmic variables the accreted matter forms an accretion disk around the white dwarf. In the boundary layer between the white dwarf and the accretion disk the accreted matter decelerates from Keplerian velocities to the rotation velocity of the white dwarf. If the accretion rate is high the boundary layer would be optically thick and cool (T ~ 105K), and if the accretion rate is low the boundary layer would be optically thin and hot (T ~ 108K) (Pringle & Savonije 1979).There are several observational problems with this simple picture: a soft X-ray component could only be detected so far in 5 dwarf novae in outburst and not in any nova-like variable. Also in high-accretion-rate systems there is a hot optically thin X-ray source, which has, however, an X-ray luminosity which is much less than the UV luminosity of the system (van Teeseling & Verbunt 1994). Finally, there is evidence for orbital modulation in the X-rays from some systems (e.g. van Teeseling et al. 1995).

scholarly journals Two Types of X-ray Spectra in Cataclysmic Variables

2004 ◽  
Vol 190 ◽  
pp. 113-119
Author(s):  
K. Mukai ◽  
A. Kinkhabwala ◽  
J. R. Peterson ◽  
S. M. Kahn ◽  
F. Paerels
Keyword(s):  
Flow Model ◽  
Cataclysmic Variables ◽  
Line Emission ◽  
Maximum Temperature ◽  
X Ray ◽  
Cooling Flow ◽  
Intermediate Polars ◽  
Photoionized Plasma ◽  
Ion Emission ◽  
Photoionization Model

AbstractWe present Chandra HETG spectra of seven cataclysmic variables, including four intermediate polars. We find that they divide unambiguously into two distinct types. Spectra of the first type (nonmagnetic systems and EX Hya) are remarkably well fit by a simple cooling flow model, which assumes only steady-state isobaric radiative cooling. The maximum temperature, kTmax, and the normalization, which provides a highly precise measurement of the accretion rate, are the only free parameters of this model. Spectra of the second type (the three other IPs) are grossly inconsistent with a cooling flow model. They instead exhibit a hard continuum, and show strong H-like and He-like ion emission but little Fe L-shell emission, which is consistent with expectations for line emission from a photoionized plasma. Using a simple photoionization model, we argue that the observed line emission for these sources can be driven entirely by the hard continuum. The physical significance of these two distinct types of X-ray spectra is also explored.

scholarly journals Chandra X-Ray Results on V426 Ophiuchi

2004 ◽  
Vol 194 ◽  
pp. 176-177
Author(s):  
Lee Homer ◽  
Paula Szkody ◽  
John C. Raymond ◽  
Robert E. Fried ◽  
D. W. Hoard ◽  
...  
Keyword(s):  
High Resolution ◽  
White Dwarf ◽  
Flow Model ◽  
Signal To Noise ◽  
X Ray ◽  
Cooling Flow ◽  
Spin Period

AbstractFrom a 45ks Chandra observation of V42G Oph we have obtained high-resolution X-ray spectra at moderate signal-to-noise, and a, good quality, uninterrupted lightcurve. The spectra are reasonably fit with a cooling flow model, similar to EX Hya and U Gem. Our analysis of the Chandra and additional X-ray/optical lightcurves reveals a persistent modulation at 4.2 hr from 1988 to 2003, likely the white dwarf spin period indicating an intermediate polar nature for V426 Oph.

scholarly journals An ASCA Observation of the Eclipsing Dwarf Nova HT Cas

1996 ◽  
Vol 158 ◽  
pp. 269-272
Author(s):  
K. Mukai ◽  
E. M. Schlegel ◽  
J. H. Swank ◽  
T. Naylor ◽  
Janet H. Wood
Keyword(s):  
Boundary Layer ◽  
White Dwarf ◽  
X Rays ◽  
X Ray ◽  
Dwarf Nova

AbstractWe report on a 1-day ASCA observation of the eclipsing dwarf nova HT Cas. We confirm the presence of an X-ray eclipse, which is narrow and deep. The data are consistent with the X-rays originating entirely from the immediate neighborhood of the white dwarf. We draw some preliminary conclusions on the boundary layer and other relevant issues.

scholarly journals Maximum mass ratio of am CVn-type binary systems and maximum white dwarf mass in ultra-compact x-ray binaries (addendum - Serb. Astron. J. No. 183 (2011), 63)

2012 ◽  
pp. 105-107
Author(s):  
B. Arbutina
Keyword(s):  
Mass Transfer ◽  
White Dwarf ◽  
Binary Systems ◽  
Accretion Rate ◽  
Practical Relevance ◽  
Maximum Mass ◽  
Mass Ratio ◽  
X Ray ◽  
The Stability ◽  
X Ray Binaries

We recalculated the maximum white dwarf mass in ultra-compact X-ray binaries obtained in an earlier paper (Arbutina 2011), by taking the effects of super-Eddington accretion rate on the stability of mass transfer into account. It is found that, although the value formally remains the same (under the assumed approximations), for white dwarf masses M2 >~0.1MCh mass ratios are extremely low, implying that the result for Mmax is likely to have little if any practical relevance.

scholarly journals Study of the reflection spectrum of the bright atoll source GX 3 + 1 with NuSTAR

2019 ◽  
Vol 487 (4) ◽  
pp. 5441-5449
Author(s):  
Aditya S Mondal ◽  
G C Dewangan ◽  
B Raychaudhuri
Keyword(s):  
Boundary Layer ◽  
Accretion Rate ◽  
Broad Band ◽  
X Ray ◽  
Upper Limit ◽  
Reflection Model ◽  
Single Temperature ◽  
Low Mass ◽  
October 17 ◽  
Spectral State

ABSTRACT We report on the NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray binary GX 3 + 1 performed on 2017 October 17. The source was found in a soft X-ray spectral state with 3–70 keV luminosity of LX ∼ 3 × 1037 erg s−1 (${\sim } 16{{\ \rm per\ cent}}$ of the Eddington luminosity), assuming a distance of 6 kpc. A positive correlation between intensity and hardness ratio suggests that the source was in the banana branch during this observation. The broad-band 3–70 keV NuSTAR spectral data can be described by a two-component continuum model consisting of a disc blackbody (kTdisc ∼ 1.8 keV) and a single temperature blackbody model (kTbb ∼ 2.7 keV). The spectrum shows a clear and robust indication of relativistic reflection from the inner disc which is modelled with a self-consistent relativistic reflection model. The accretion disc is viewed at an inclination of i ≃ 22°–26° and extended close to the NS, down to $R_\text{in}=(1.2\!-\!1.8) R_\text{ISCO}\:(\simeq 6.1\!-\!9.1\, R_{\mathrm{ g}}\: \text{or}\: 14\!-\!20.5$ km) which allows an upper limit on the NS radius (≤13.5 km). Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼6.3 Rg from the NS surface. However, if the disc is not truncated by the boundary layer but by the magnetosphere, an estimated upper limit on the polar magnetic field would be of B ≤ 6 × 108 G.

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.

Supersoft Sources

1998 ◽  
Vol 11 (2) ◽  
pp. 790-793 ◽  
Author(s):  
P. Kahabka
Keyword(s):  
White Dwarf ◽  
Milky Way ◽  
Accretion Rate ◽  
X Rays ◽  
X Ray ◽  
Galactic Source ◽  
Nuclear Burning ◽  
Cooling Phase ◽  
The Stability ◽  
Stability Line

Supersoft X-ray sources are a new class of luminous X-ray binaries discovered with the X-ray telescopes of the Einstein and ROSAT satellites and extensively studied in the optical with ground based telescopes, in the UV with IUE and HST and in X-rays with ROSAT, Beppo-SAX and ASCA (cf. Kahabka & van den Heuvel 1997, van Teeseling 1997). The luminosities derived for a first sample of supersoft sources studied with moderate resolution X-ray spectroscopy (using Beppo-SAX LECS and ASCA SIS detectors, Parmar et al. 1997, Ebisawa et al. 1997) have been predicted to follow Iben’s stability line (Iben 1982), i.e. the location in the Hertzsprung-Russell diagram which separates the plateau phase from the cooling phase. This is not unreasonable as any system experiencing steady-state accretion, i.e. accretion at a rate equalling about the nuclear burning rate will be found close to the stability line. If the accretion rate exceeds this limit then the white dwarf gets bloated and disappears in X-rays. If the accretion rate falls below this limit the white dwarf envelope cools, the luminosity as well as the temperature ceases and the source enters unstable recurrent nuclear burning. From the population synthesis calculations of Yungelson (1996) follows that there exit for the Milky Way a few sources at any epoch which are more massive than 1.2 MQ. They are expected to be extremely X-ray bright and may be standard candles (cf. Table 1 and Figure 1 for the brightest known supersoft sources per galaxy Milky Way to NGC 55). Their spectral distribution is expected to be similar to that of the extremely hot galactic source RXJ0925.7-4758 (it peaks at 1 keV and the flux is distributed from 0.5 to 2 keV, see Figure 2 for the ASCA spectrum of RX J0925.7-4758 (and CAL 87) as derived by Ebisawa et al. 1997).

scholarly journals Multi-Wavelength Predictions of the DIM

2004 ◽  
Vol 194 ◽  
pp. 257-257
Author(s):  
M. R. Schreiber ◽  
J.-M. Hameury ◽  
J.-P. Lasota
Keyword(s):  
Boundary Layer ◽  
White Dwarf ◽  
Hot Spot ◽  
Optical Emission ◽  
Local Spectrum ◽  
X Ray ◽  
Multi Wavelength ◽  
On Line ◽  
Extreme Uv ◽  
Reasonable Model

Using the disc instability model (DIM) and a simple but reasonable model for the X-ray, extreme UV, UV and optical emission we investigate the multi-wavelength properties of dwarf novae. We discuss the predictions of the model in the context of the observationally best studied systems, i.e. SS Cyg and VW Hyi. We use the version of the DIM described in Buat-Ménard et al. (2001). The local spectrum of the emission from the disc is assumed to be given by Kurucz (1993,VizieR On-line Data Catalog). We also take into account emission from the (irradiated) secondary, the white dwarf, the hot spot, and the boundary layer.

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