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991.
992.
Wynn C. G. Ho † David L. Kaplan ‡ Philip Chang Matthew van Adelsberg Alexander Y. Potekhin 《Monthly notices of the Royal Astronomical Society》2007,375(3):821-830
RX J1856.5−3754 is one of the brightest nearby isolated neutron stars (INSs), and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5−3754, within the uncertainties. In our simplest model, the best-fitting parameters are an interstellar column density N H ≈ 1 × 1020 cm−2 and an emitting area with R ∞ ≈ 17 km (assuming a distance to RX J1856.5−3754 of 140 pc), temperature T ∞ ≈ 4.3 × 105 K , gravitational redshift z g ∼ 0.22 , atmospheric hydrogen column y H ≈ 1 g cm−2 , and magnetic field B ≈ (3–4) × 1012 G ; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the NS surface as well as general relativistic effects, to determine pulsations; we find that there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5−3754. 相似文献
993.
M. T. Rushton T. R. Geballe A. V. Filippenko R. Chornock W. Li D. C. Leonard † R. J. Foley A. Evans B. Smalley J. Th. van Loon S. P. S. Eyres 《Monthly notices of the Royal Astronomical Society》2005,360(4):1281-1289
We report optical and near-infrared spectroscopy, and optical spectropolarimetry, of the peculiar variable V838 Mon during the multiple outburst phase in early 2002. The spectral evolution is exceptional. Our earliest spectra (2002 January) are noteworthy for their strong absorption lines of barium and strontium in the optical, and bands of CO and circumstellar H2 O in the near-infrared. All but the CO weaken or are absent in later spectra. The behaviour of the CO band during this phase is extraordinary: initially in absorption, it was observed two months later in optically thick emission. The excitation of the CO is probably the result of the propagation of a shock wave at the third maximum. The two spectropolarimetric epochs were taken 6 and 27 d after the second outburst on 2002 February 8. The polarization at both times was measured to be pV ≈ 2.7 per cent. Nearly all of the measured polarization is believed to be due to interstellar dust, a conclusion that is consistent with previous studies. At both epochs, however, a weak and variable intrinsic component is thought to be present. Between January and March of 2002 the luminosity of V838 Mon increased by a factor of 15 and the apparent diameter increased fourfold. 相似文献
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R. P. Fender T. J. Maccarone Z. van Kesteren 《Monthly notices of the Royal Astronomical Society》2005,360(3):1085-1090
Drawing on recent estimates of the power of jets from X-ray binary systems as a function of X-ray luminosity, combined with improved estimates of the relevant log( N )–log( L X ) luminosity functions, we calculate the total energy input to the interstellar medium (ISM) from these objects. The input of kinetic energy to the ISM via jets is dominated by those of the black hole systems, in contrast to the radiative input, which is dominated by accreting neutron stars. Summing the energy input from black hole jets L J in the Milky Way, we find that it is likely to correspond to ≥1 per cent of L SNe , the time-averaged kinetic luminosity of supernovae, and ≥5 per cent of L CR , the cosmic ray luminosity. Given uncertainties in jet power estimates, significantly larger contributions are possible. Furthermore, in elliptical galaxies with comparable distributions of low mass X-ray binaries, but far fewer supernovae, the ratio L J / L SNe is likely to be larger by a factor of ∼5. We conclude that jets from X-ray binaries may be an important, distributed, source of kinetic energy for the ISM in the form of relativistic shocks, and as a result are likely to be a major source of cosmic rays. 相似文献
998.
Yun Li H. J. Mo Frank C. van den Bosch W. P. Lin 《Monthly notices of the Royal Astronomical Society》2007,379(2):689-701
We study the mass assembly history (MAH) of dark matter haloes. We compare MAHs obtained using (i) merger trees constructed with the extended Press–Schechter (EPS) formalism, (ii) numerical simulations and (iii) the Lagrangian perturbation code pinocchio . We show that the pinocchio MAHs are in excellent agreement with those obtained using numerical simulations, while the EPS formalism predicts MAHs that occur too late. pinocchio , which is much less CPU intensive than N -body simulation, can be run on a simple personal computer, and does not require any labour intensive post-simulation analysis, therefore provides a unique and powerful tool to investigate the growth history of dark matter haloes. Using a suite of 55 pinocchio simulations, with 2563 particles each, we study the MAHs of 12 924 cold dark matter (CDM) haloes in a ΛCDM concordance cosmology. This is by far the largest set of haloes used for any such analysis. For each MAH we derive four different formation redshifts, which characterize different epochs during the assembly history of a dark matter halo. We show that haloes less massive than the characteristic non-linear mass scale establish their potential wells much before they acquire most of their mass. The time when a halo reaches its maximum virial velocity roughly divides its mass assembly into two phases, a fast-accretion phase which is dominated by major mergers, and a slow-accretion phase dominated by minor mergers. Each halo experiences about 3 ± 2 major mergers since its main progenitor had a mass equal to 1 per cent of the final halo mass. This major merger statistic is found to be virtually independent of halo mass. However, the average redshift at which these major mergers occur is strongly mass dependent, with more massive haloes experiencing their major mergers later. 相似文献
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