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1.
We have computed a spherically symmetric model for the interaction of matter ejected during the outburst of a classical nova with the stellar wind from its optical component. This model is used to describe the intense X-ray outburst (the peak 3–20 keV flux was ~2 Crab) of the binary system CI Camelopardalis in 1998. According to our model, the stellar wind from the optical component heated by a strong shock wave produced when matter is ejected from the white dwarf as the result of a thermonuclear explosion on its surface is the emission source in the standard X-ray band. Comparison of the calculated and observed time dependences of the mean radiation temperature and luminosity of the binary system during its outburst has yielded very important characteristics of the explosion. We have been able to measure the velocity of the ejected matter immediately after the onset of the explosion for the first time: it follows from our model that the ejected matter had a velocity of ~2700 km s?1 even on 0.1–0.5 day after the outburst onset and it flew with such a velocity for the first 1–1.5 day under an external force, possibly, the radiation pressure from the white dwarf. Subsequently, the matter probably became transparent and began to decelerate. The time dependence of the mean radiation temperature at late expansion phases has allowed us to estimate the mass of the ejected matter, ~10?7–10?6 M ⊙. The mass loss rate in the stellar wind required to explain the observed peak luminosity of the binary system during its outburst has been estimated to be \(\dot M\) ~ (1 ? 2) × 10?6 M ⊙ yr?1. 相似文献
2.
Rajmal Jain Vishal Joshi Yoichiro Hanaoka T. Sakurai Nipa Upadhyay 《Journal of Astrophysics and Astronomy》2006,27(2-3):339-346
We present a study of 10 microflares observed in 4–30 keV by SOXS mission simultaneously with Hα observations made at NAOJ,
Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares
varies between 4 and 25 min. We found that the X-ray emission in all microflares under study in the dynamic energy range of
4–30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4 keV, low
level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 keV. We also observed the Fe line complex
features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature
of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2x1049 cm-3. Non-thermal (NT) emission appeared in the energy range 7–15 keV with exponent -6.8 ≤γ≤-4.8. Our study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces
recurrent microflare activity of a similar nature. We concluded from X-ray and simultaneous Hα observations that the microflares
are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection
heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα
bright kernels. 相似文献
3.
Roberto F. Viotti Lucio Angelo Antonelli Sonja Rebecchi Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22
We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary
system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse,
this component was the same as outside eclipse, but for a large (×3.5) increase of NH
h
, that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly,
at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV
spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal
emission as an alternative model for the core source. 相似文献
4.
The accretion of matter onto stars formed by carbon-oxygen cores triggers hydrogen flicker. The development of hydrogen flicker and the shock generation associated therewith are discussed. If the matter thus ejected is halted by a dense gas surrounding a star, a corona of high temperature is formed. This may take place in dense planetary nebulae and is regarded as an origin of starlike X-ray sources. More violent hydrogen flicker takes place at white dwarfs and may be an origin of novae. Nuclear-reaction products ejected are positron sources and they may provide MeV positrons as strong as 10–3 cm–2 sec–1 sr–1. Nuclides produced by hydrogen flicker and a part of the carbon-oxygen core ejected may contribute to galactic cosmic rays; their chemical composition is like that observed in cosmic rays. 相似文献
5.
Energetic particles, ejected from the Sun during solar flare events, may encounter interplanetary plasma/field conditions, which deviate considerably from the quiet time values used normally to describe the particle propagation. This is due to the presence of a hydromagnetic shock, which is emitted from the Sun at the time of the explosion. In a theoretical blast wave model, which incorporates the interaction with plane polarized Alfvén waves, we have analysed the changes in different terms of the Fokker-Planck equation, which describes energetic particle propagation. In this treatment, the shock influence on energy changes and on the transport coefficients are discussed. 相似文献
6.
We investigate the effect of exotic matter in particular, hyperon matter on neutron star properties such as equation of state
(EoS), mass-radius relationship and bulk viscosity. Here we construct equations of state within the framework of a relativistic
field theoretical model. As hyperons are produced abundantly in dense matter, hyperon–hyperon interaction becomes important
and is included in this model. Hyperon–hyperon interaction gives rise to a softer EoS which results in a smaller maximum mass
neutron star compared with the case without the interaction. Next we compute the coefficient of bulk viscosity and the corresponding
damping time scale due to the non-leptonic weak process including Λ hyperons. Further, we investigate the role of the bulk
viscosity on gravitational radiation driven r-mode instability in a neutron star of given mass and temperature and find that
the instability is effectively suppressed.
相似文献
7.
We analyze the high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over
the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. The drifting structures take place before the soft
X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind
of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s−1. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller
ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of
each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has
an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted
to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is
possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio
imaging observation would be needed. 相似文献
8.
U. Mukherjee S. Bapna H. Raichur B. Paul S. N. A. Jaaffrey 《Journal of Astrophysics and Astronomy》2006,27(1):25-35
We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034
during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter
Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected
the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution
of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency
and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged
X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation
in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with
pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum
is well fitted with a model consisting of a cut-off power law along with an iron emission line. 相似文献
9.
We present the X-ray light curve in the 0.2–2.4 keV band based on fiveROSAT observations of SN1978K in NGC 1313. The X-ray emission is believed to arise from the interaction of the reverse shock and the expanding debris from the supernova. The reverse shock becomes established after the outgoing shock runs into circumstellar matter. 相似文献
10.
U. Mukherjee H. Raichur B. Paul S. Naik N. Bhatt 《Journal of Astrophysics and Astronomy》2006,27(4):411-423
We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several
binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis
with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters
determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray
binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital
phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range
were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted
energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The
variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column
density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a
spherically symmetric stellar wind from the companion star. 相似文献
11.
Alaa I. Ibrahim Hisham Anwer Mohamed H. Soliman Nicholas Mackie-Jones Kalvir S. Dhuga William C. Parke Jean H. Swank Tilan Ukwatta M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):535-539
A 6.4 keV emission line was discovered in an unusual burst from the soft gamma repeater SGR 1900+14 with the Rossi X-ray Timing
Explorer (RXTE). The line was detected in part of a complex multipeak precursor that preceded the unusual burst of 1998 August
29, i.e. two days after the giant flare of August 27 from the source. The origin of the line was not firmly identified and
two possible interpretations were equally plausible including (a) Kα fluorescence from a small iron rich material that was ejected to the magnetosphere during the August 27 flare, and (b) proton
or α-particle cyclotron resonance. If the iron scenario was correct, we expect to find evidence for the line during the intervening
interval between the flare and the August 29 burst, i.e. on August 28. Here we present the results of the August 28 burst
observation, taken with RXTE. We detect a total of seven bursts whose individual and joint spectra do not show evidence for
spectral lines. We also investigated a sample of nine bursts before and after the August 29 burst (from 1998 June to December)
that do not reveal evidence for a spectral line near 6.4 keV or elsewhere. These results disfavor the iron scenario and make
the proton/α-particle cyclotron resonance interpretation more plausible. The appearance of the emission line in part of a complex burst
and its absence from the studied sample indicate that the line is likely due to a transient phenomenon that may depend on
the burst morphology, energetics and the properties of the emission region.
相似文献
12.
13.
Cindy R. Tam Victoria M. Kaspi Bryan M. Gaensler Eric V. Gotthelf 《Astrophysics and Space Science》2007,308(1-4):519-523
The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous
X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient
pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle
of AX J1845.0-0258’s discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its
spectrum is well described by an absorbed single-component blackbody (kT∼2.0 keV) or power law (Γ∼1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period
of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653
is considerably harder: if truly the counterpart, then its spectral behavior is contrary to that seen in the established transient
AXP XTE J1810-197, which softened from kT∼0.67 keV to ∼0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an
unrelated source, and we discuss the implications for AXPs, and magnetars in general.
相似文献
14.
The Bastille Day (14 July) 2000 CME is a fast, halo coronal mass ejection event headed earthward. The ejection reached Earth
on 15 July 2000 and produced a very significant magnetic storm and widespread aurora. At 1 AU the Wind spacecraft recorded a strong forward shock with a speed jump from ∼ 600 to over 1000 km s−1. About 6 months later, this CME-driven shock arrived at Voyager 2 (∼ 63 AU) on 12 January 2001 with a speed jump of ∼ 60 km s−1. This provides a good opportunity to study the shock propagation in the outer heliosphere. In this study, we employ a 2.5-D
MHD numerical model, which takes the interaction of solar wind protons and interstellar neutrals into account, to investigate
the shock propagation in detail and compare the model predictions with the Voyager 2 observations. The Bastille Day CME shock undergoes a dramatic change in character from the inner to outer heliosphere. Its
strength and propagation speed decay significantly with distance. The model results at the location of Voyager 2 are in good agreement with in-situ observations.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014293527951 相似文献
15.
S. L. Skinner S. A. Zhekov M. Güdel W. Schmutz 《Monthly notices of the Royal Astronomical Society》2007,378(4):1491-1498
We present results of an ≈20-ks X-ray observation of the Wolf–Rayet (WR) binary system WR 147 obtained with XMM–Newton . Previous studies have shown that this system consists of a nitrogen-type WN8 star plus an OB companion whose winds are interacting to produce a colliding wind shock. X-ray spectra from the pn and MOS detectors confirm the high extinction reported from infrared studies and reveal hot plasma including the first detection of the Fe Kα line complex at 6.67 keV. Spectral fits with a constant-temperature plane-parallel shock model give a shock temperature kT shock = 2.7 keV ( T shock ≈ 31 MK), close to but slightly hotter than the maximum temperature predicted for a colliding wind shock. Optically thin plasma models suggest even higher temperatures, which are not yet ruled out. The X-ray spectra are harder than can be accounted for using 2D numerical colliding wind shock models based on nominal mass-loss parameters. Possible explanations include: (i) underestimates of the terminal wind speeds or wind abundances, (ii) overly simplistic colliding wind models or (iii) the presence of other X-ray emission mechanisms besides colliding wind shocks. Further improvement of the numerical models to include potentially important physics such as non-equilibrium ionization will be needed to rigorously test the colliding wind interpretation. 相似文献
16.
We have detected X-ray emission (1 keV) from young intermediate-mass stars (Herbig Ae/Be stars). Since these stars are not supposed to produce intrinsic X-ray emission (no convection, no coronae), we believe that our results suggest that the X-ray emission actually traces the shock interaction of the Ae/Be star stellar winds with remnant circumstellar matter left over from the star formation process, the presence of which is also indicated by far-infrared (IRAS) and submm/mm continuum data. 相似文献
17.
We consider sterile neutrinos as a component of dark matter in the Milky Way and clusters, and compare their rest mass, decay
rate and the mixing angle. A radiative decaying rate of order Γ∼10−19 s−1 for sterile neutrino rest mass m
s
=18–19 keV can satisfactorily account for the cooling flow problem and heating source in Milky Way center simultaneously.
Also, these ranges of decay rate and rest mass match the prediction of the mixing angle sin 22θ∼10−3 with a low reheating temperature in the inflation model, which enables the sterile-active neutrino oscillation to be visible
in future experiments. However, decaying sterile neutrinos have to be ruled out as a major component of dark matter because
of the high decay rate. 相似文献
18.
The goal of this paper is to determine the characteristic cooling time of the accretion flowmatter near the surface of the magnetic white dwarf in the binary system EX Hya. Most of the X-ray photons in such binary systems are produced in an optically thin hot plasma with a temperature above 10 keV heated when the matter passes through the shock near the white dwarf surface. The total X-ray luminosity is determined by the matter accumulated below the shock in its cooling time. Thus, the X-ray luminosity variability related to the variations in the accretion rate onto the white dwarf surface must be suppressed at frequencies higher than the inverse cooling time. If the optically thin plasma radiation dominates in the rate of energy losses by the heated matter, which is true for white dwarfs with moderately strong magnetic fields, less than 1–10 MG, then the matter cooling time can give an estimate of the matter density in the accretion column. Given the accretion rate and the matter density in the accretion column at the white dwarf surface, the area of the accretion channel can be estimated. We have analyzed all of the currently available observational data for one of the brightest intermediate polars in the X-ray sky, EX Hya, from the RXTE and XMM-Newton observatories. The power spectra of its aperiodic variability have given an upper limit on the cooling time of the hot plasma: <1.5–2 s. For the observed accretion rate, ×1015 g s?1, this corresponds to a matter density below the shock surface ?1016 cm?3 and an area of the base of the accretion channel no more than <4.6 × 1015 cm2. Using the information about the maximum geometrical size of the accretion channel obtained by analyzing X-ray eclipses in the binary system EX Hya, we have derived an upper limit on the thickness of the flow over the surface of the magnetosphere near the white dwarf surface, ?3 × 106 cm, and the plasma penetration depth at the magnetospheric boundary, Δr/r ? 6 × 10?3. 相似文献
19.
Alaa I. Ibrahim William C. Parke Jean H. Swank Hisham Anwer Roberto Turolla Silvia Zane M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):43-50
The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with
the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single
and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law,
optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at
∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for
the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the
5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice
of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high
confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in
the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account
for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1)
they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid
varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated
red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together
with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.
相似文献
20.
Rajmal Jain Vishal Joshi S. L. Kayasth Hemant Dave M. R. Deshpande 《Journal of Astrophysics and Astronomy》2006,27(2-3):175-192
We present the first results from the ‘Low Energy Detector’ pay-load of ‘Solar X-ray Spectrometer (SOXS)’ mission, which was
launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The SOXS Low Energy
Detector (SLD) payload was designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with
Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of the Indian Space Research Organization
(ISRO). The SLD payload employs the state-of-the-art solid state detectors viz., Si PIN and Cadmium-Zinc-Telluride (CZT) devices
that operate at near room temperature (-20°C). The dynamic energy range of Si PIN and CZT detectors are 4–25 keV and 4–56
keV respectively. The Si PIN provides sub-keV energy resolution while CZT reveals ∼1.7keV energy resolution throughout the
dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows the measuring of the intensity,
peak energy and equivalent width of the Fe-line complex at approximately 6.7 keV as a function of time in all 8 M-class flares
studied in this investigation. The peak energy (E
p) of Fe-line feature varies between 6.4 and 6.8 keV with increase in temperature from 9 to 34 MK. We found that the equivalent
width (ω) of Fe-line feature increases exponentially with temperature up to 20 MK but later it increases very slowly up to
28 MK and then it remains uniform around 1.55 keV up to 34 MK. We compare our measurements ofw with calculations made earlier by various investigators and propose that these measurements may improve theoretical models.
We interpret the variation of both Epand ω with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval
and as a consequence the contribution from different ionic emission lines also varies. 相似文献