共查询到20条相似文献,搜索用时 15 毫秒
1.
P. Elebert M. T. Reynolds P. J. Callanan D. J. Hurley G. Ramsay F. Lewis D. M. Russell B. Nord S. R. Kane D. L. DePoy P. Hakala 《Monthly notices of the Royal Astronomical Society》2009,395(2):884-894
We present phase resolved optical spectroscopy and photometry of V4580 Sagittarii, the optical counterpart to the accretion powered millisecond pulsar SAX J1808.4−3658, obtained during the 2008 September/October outburst. Doppler tomography of the N iii λ4640.64 Bowen blend emission line reveals a focused spot of emission at a location consistent with the secondary star. The velocity of this emission occurs at 324 ± 15 km s−1 ; applying a ' K -correction', we find the velocity of the secondary star projected on to the line of sight to be 370 ± 40 km s−1 . Based on existing pulse timing measurements, this constrains the mass ratio of the system to be 0.044+0.005 −0.004 , and the mass function for the pulsar to be 0.44+0.16 −0.13 M⊙ . Combining this mass function with various inclination estimates from other authors, we find no evidence to suggest that the neutron star in SAX J1808.4−3658 is more massive than the canonical value of 1.4 M⊙ . Our optical light curves exhibit a possible superhump modulation, expected for a system with such a low mass ratio. The equivalent width of the Ca ii H and K interstellar absorption lines suggest that the distance to the source is ∼2.5 kpc. This is consistent with previous distance estimates based on type-I X-ray bursts which assume cosmic abundances of hydrogen, but lower than more recent estimates which assume helium-rich bursts. 相似文献
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J. G. Greenhill A. B. Giles C. Coutures 《Monthly notices of the Royal Astronomical Society》2006,370(3):1303-1308
The optical counterpart of the transient, millisecond X-ray pulsar SAX J1808.4–3658 was observed in four colours ( BVRI ) for five weeks during the 2005 June–July outburst. The optical fluxes declined by ∼2 mag during the first 16d and then commenced quasi-periodic secondary outbursts, with time-scales of several days, similar to those seen in 2000 and 2002. The broad-band spectra derived from these measurements were generally consistent with emission from an X-ray heated accretion disc. During the first 16d decline in intensity the spectrum became redder. We suggest that the primary outburst was initiated by a viscosity change driven instability in the inner disc and note the contrast with another accreting millisecond pulsar, XTE J0929−314, for which the spectrum becomes bluer during the decline. On the night of 2005 June 5 (HJD 245 3527) the I -band flux was ∼0.45-mag brighter than on the preceding or following nights whereas the BV and R bands showed no obvious enhancement. A type I X-ray burst was detected by the Rossi X-ray Timing Explorer spacecraft during this I -band integration. It seems unlikely that reprocessed radiation from the burst was sufficient to explain the observed increase. We suggest that a major part of the I -band excess was due to synchrotron emission triggered by the X-ray burst. Several other significant short duration changes in V − I were detected. One occurred at about HJD 245 3546 in the early phase of the first secondary outburst and may be due to mass-transfer instability or to another synchrotron emission event. 相似文献
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We present results from a pulse timing analysis of the accretion-powered millisecond X-ray pulsar SAX J1808.4-3658 using X-ray
data obtained during four outbursts of this source. Extensive observations were made with the proportional counter array of
the Rossi X-ray Timing Explorer (RXTE) during the four outbursts that occurred in 1998, 2000, 2002 and 2005. Instead of measuring
the arrival times of individual pulses or the pulse arrival time delay measurement that is commonly used to determine the
orbital parameters of binary pulsars, we have determined the orbital ephemeris during each observation by optimizing the pulse
detection against a range of trial ephemeris values. The source exhibits a significant pulse shape variability during the
outbursts. The technique used by us does not depend on the pulse profile evolution, and is therefore, different from the standard
pulse timing analysis. Using 27 measurements of orbital ephemerides during the four outbursts spread over more than 7 years
and more than 31,000 binary orbits, we have derived an accurate value of the orbital period of 7249.156862(5) s (MJD = 50915)
and detected an orbital period derivative of (3.14 ± 0.21) × 10−12 s s−1. We have included a table of the 27 mid-eclipse time measurements of this source that will be valuable for further studies
of the orbital evolution of the source, especially with ASTROSAT. We point out that the measured rate of orbital period evolution
is considerably faster than the most commonly discussed mechanisms of orbital period evolution like mass transfer, mass loss
from the companion star and gravitational wave radiation. The present time scale of orbital period change, 73 Myr is therefore
likely to be a transient high value of period evolution and similar measurements during subsequent outbursts of SAX J1808.4-3658
will help us to resolve this. 相似文献
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R. Kaur Rudy Wijnands Alessandro Patruno Vincenzo Testa GianLuca Israel Nathalie Degenaar Biswajit Paul Brijesh Kumar 《Monthly notices of the Royal Astronomical Society》2009,394(3):1597-1604
We present results from our Chandra and XMM–Newton observations of two low-luminosity X-ray pulsators SAX J1324.4−6200 and SAX J1452.8−5949 which have spin periods of 172 and 437 s, respectively. The XMM–Newton spectra for both sources can be fitted well with a simple power-law model of photon index, Γ∼ 1.0 . A blackbody model can equally well fit the spectra with a temperature, kT ∼ 2 keV, for both sources. During our XMM–Newton observations, SAX J1324.4−6200 is detected with coherent X-ray pulsations at a period of 172.86 ± 0.02 s while no pulsations with a pulse fraction greater than 18 per cent (at 95 per cent confidence level) in 0.2–12 keV energy band are detected in SAX J1452.8−5949 . The spin period of SAX J1324.4−6200 is found to be increasing on a time-scale of which would suggest that the accretor is a neutron star and not a white dwarf. Using subarcsec spatial resolution of the Chandra telescope, possible counterparts are seen for both sources in the near-infrared images obtained with the son of infrared spectrometer and array camera (SOFI) instrument on the New Technology Telescope. The X-ray and near-infrared properties of SAX J1324.4−6200 suggest it to be a persistent high-mass accreting X-ray pulsar at a distance ≤8 kpc . We identify the near-infrared counterpart of SAX J1452.8−5949 to be a late-type main-sequence star at a distance ≤10 kpc, thus ruling out SAX J1452.8−5949 to be a high-mass X-ray binary. However, with the present X-ray and near-infrared observations, we cannot make any further conclusive conclusion about the nature of SAX J1452.8−5949 . 相似文献
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M. G. Revnivtsev 《Astronomy Letters》2003,29(6):383-386
Analysis of the RXTE slew data in October 1996 revealed a weak X-ray burst from the millisecond pulsar SAX J 1808.4-3658. The 3–20-keV energy spectrum of the source can be described by a power law with an index of 2.0 and a(3-to 20 keV) luminosity of ~1.4×1035 erg s?1 (the distance to the source was taken to be 2.5 kpc). Because of the short exposure time, we failed to detect weak pulsations at a frequency of 401 Hz in the source. The (2σ) upper limit of the pulse fraction is ~13%. 相似文献
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J. Casares G. Dubus T. Shahbaz C. Zurita P.A. Charles 《Monthly notices of the Royal Astronomical Society》2002,329(1):29-36
We present Very Large Telescope (VLT) low-resolution spectroscopy of the neutron star X-ray transient XTE J2123−058 during its quiescent state. Our data reveal the presence of a K7V companion which contributes 77 per cent to the total flux at λ 6300 and orbits the neutron star at . Contrary to other soft X-ray transients (SXTs), the H α emission is almost exactly in antiphase with the velocity curve of the optical companion. Using the light-centre technique we obtain and hence This, combined with a previous determination of the inclination angle yields and . M 2 agrees well with the observed spectral type. Doppler tomography of the H α emission shows a non-symmetric accretion disc distribution mimicking that seen in SW Sex stars. Although we find a large systemic velocity of − this value is consistent with the galactic rotation velocity at the position of J2123−058, and hence a halo origin. The formation scenario of J2123−058 is still unresolved. 相似文献
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S. Ç. nam L. J. Townsend V. A. McBride A. Baykal M. J. Coe R. H. D. Corbet 《Monthly notices of the Royal Astronomical Society》2009,395(3):1662-1668
We analysed Rossi X-ray Timing Explorer Proportional Counter Array observations of a recent outburst of the X-ray pulsar XMMU J054134.7−682550. We calculated the pulse frequency history of the source. We found no sign of a binary companion. The source spins up when the X-ray flux is higher, with a correlation between the spin-up rate and X-ray flux, which may be interpreted as a sign of an accretion disc. On the other hand, the source was found to have an almost constant spin frequency when the X-ray flux is lower without any clear sign of a spin-down episode. The decrease in pulsed fraction with decreasing X-ray flux was interpreted as a sign of accretion geometry change, but we did not find any evidence of a transition from accretor to propeller regimes. The source was found to have variable pulse profiles. Two peaks in pulse profiles were usually observed. We studied the X-ray spectral evolution of the source throughout the observation. Pulse-phase-resolved analysis does not provide any further evidence for a cyclotron line, but may suggest a slight variation of intensity and width of the 6.4 keV iron line with phase. 相似文献
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Marek Gierliski Juri Poutanen † 《Monthly notices of the Royal Astronomical Society》2005,359(4):1261-1276
We have undertaken an extensive study of X-ray data from the accreting millisecond pulsar XTE J1751 − 305 observed by RXTE and XMM–Newton during its 2002 outburst. In all aspects this source is similar to the prototypical millisecond pulsar SAX J1808.4 − 3658, except for the higher peak luminosity of 13 per cent of Eddington, and the optical depth of the hard X-ray source, which is larger by a factor ∼2. Its broad-band X-ray spectrum can be modelled by three components. We interpret the two soft components as thermal emission from a colder ( kT ∼ 0.6 keV) accretion disc and a hotter (∼1 keV) spot on the neutron star surface. We interpret the hard component as thermal Comptonization in plasma of temperature ∼40 keV and optical depth ∼1.5 in a slab geometry. The plasma is heated by the accretion shock as the material collimated by the magnetic field impacts on to the surface. The seed photons for Comptonization are provided by the hotspot, not by the disc. The Compton reflection is weak and the disc is probably truncated into an optically thin flow above the magnetospheric radius. Rotation of the emission region with the star creates an almost sinusoidal pulse profile with an rms amplitude of 3.3 per cent. The energy-dependent soft phase lags can be modelled by two pulsating components shifted in phase, which is naturally explained by a different character of emission of the optically thick spot and optically thin shock combined with the action of the Doppler boosting. The observed variability amplitude constrains the hotspot to lie within 3°–4° of the rotational pole. We estimate the inner radius of the optically thick accreting disc to be about 40 km. In that case, the absence of emission from the antipodal spot, which can be blocked by the accretion disc, gives the inclination of the system as ≳70°. 相似文献
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R. I.Hynes C.Zurita C. A.Haswell J.Casares P. A.Charles E. P.Pavlenko S. Yu.Shugarov D. A.Lott 《Monthly notices of the Royal Astronomical Society》2002,330(4):1009-1021
We present a spectrophotometric study of short-term optical variability in the quiescent black hole X-ray transient V404 Cyg. This includes two nights of high-time-resolution H α spectroscopy with which we resolve much of the time variability, and a further six nights of archival spectroscopy with lower time resolution but higher spectral resolution. We find significant variability in most of the data considered, with both the H α line and the continuum often varying in a correlated way. This includes both dramatic flares lasting a few hours in which the line flux nearly doubles and lower-level flickering. The strongest flares involve development of asymmetry in the line profile, with the red wing usually strongest independent of orbital phase. It is unclear why this is the case, but we discuss several possible explanations. We consider the energetics of the flares and compare with plausible models including chromospheric activity on the companion star, local magnetic reconnection events within the disc and varying irradiation from close to the black hole. Based on the line profile changes during the flares, we conclude that the most likely origin for the variability is variable photoionization by the central source, although local flares within the disc cannot be ruled out. 相似文献
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C. G. Bassa P. G. Jonker D. Steeghs M. A. P. Torres 《Monthly notices of the Royal Astronomical Society》2009,399(4):2055-2062
We present phase resolved optical spectroscopy and X-ray timing of the neutron star X-ray binary EXO 0748−676 after the source returned to quiescence in the autumn of 2008. The X-ray light curve displays eclipses consistent in orbital period, orbital phase and duration with the predictions and measurements before the return to quiescence. Hα and He i emission lines are present in the optical spectra and show the signature of the orbit of the binary companion, placing a lower limit on the radial velocity semi-amplitude of K 2 > 405 km s−1 . Both the flux in the continuum and the emission lines show orbital modulations, indicating that we observe the hemisphere of the binary companion that is being irradiated by the neutron star. Effects due to this irradiation preclude a direct measurement of the radial velocity semi-amplitude of the binary companion; in fact, no stellar absorption lines are seen in the spectrum. Nevertheless, our observations place a stringent lower limit on the neutron star mass of M 1 > 1.27 M⊙ . For the canonical neutron star mass of M 1 = 1.4 M⊙ , the mass ratio is constrained to 0.075 < q < 0.105 . 相似文献
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D. E. Calvelo S. D. Vrtilek D. Steeghs M. A. P. Torres J. Neilsen A. V. Filippenko J. I. González Hernández † 《Monthly notices of the Royal Astronomical Society》2009,399(2):539-549
We present Doppler and modulation tomography of the X-ray nova XTE J1118+480 with data obtained during quiescence using the 10-m Keck II telescope. The hotspot where the gas stream hits the accretion disc is seen in Hα, Hβ, He i λ5876 and Ca ii λ8662, thus verifying the presence of continued mass transfer within the system. The disc is clearly seen in Hα and Ca ii λ8662. We image the mass-donor star in narrow absorption lines of Na i λλ5890, 5896, 8183, 8195 and Ca ii λ8662, implying an origin from the secondary itself rather than the interstellar medium. We also detect deviations in the centroid of the double peak of Hα akin to those found by Zurita et al. suggesting disc eccentricity. 相似文献
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R. Cornelisse P. A. Charles C. Robertson 《Monthly notices of the Royal Astronomical Society》2006,366(3):918-922
We report on the properties of a 99.3-d periodic modulation in the X-ray transient XTE J1716−389. We associate this source with the transient KS J1716−389, first detected by the Mir /Kvant module in 1994. The spectral characteristics of XTE J1716−389, a high intrinsic absorption column, strong emission features and a power-law spectrum, make it very similar to the class of highly absorbed X-ray binaries detected by INTEGRAL . We associate the 99.3-d periodic behaviour with the geometrical obscuration that results from a precessing circumbinary disc that is moving in and out of the field of view, comparable to what has been proposed for SS 433. We therefore propose that XTE J1716−389 is a high-mass X-ray binary with a supergiant companion that is similar not only to SS 433, but also to the new class of highly obscured X-ray binaries, suggesting that SS 433 is a member of much wider population that is now being detected by INTEGRAL . 相似文献