Jun-han You

Further Analysis of Absorption Features in the X-Ray Spectrum of the Isolated Neutron Star 1E 1207.4–5209

Observation of the isolated neutron star 1E 1207.4-5209 shows three distinct absorption features, regularly spaced at 0.7, 1.4, and 2.1 keV, which vary in phase with the stars rotation. In this paper, we attempt to clarify the understanding of these absorption lines by using the quantum theory of the cyclotron radiation under the quadrupole approximation, given in our previous papers. We found that these lines are more likely to arise from the electron-cyclotron absorption, rather than from proton-cyclotron. We explain why the observed fundamental and the second-harmonic cyclotron features with significantly different absorption coefficients have nearly the same strength. Assuming that the absorption features arise from an approximately uniform narrow column at the bottom of the pole region of neutron star, we complete a simplified model calculation to fit the observational data; thus, the included angle between the spinning axis and the observers sight line, as well as that between the spinning and the magnetic axes of the neutron star, are determined by this method. The geometrical configuration inferred from the deduced directions of these axes is helpful to better understand the physics and some other relevant observation facts of star 1E 1207.4-5209.

Cerenkov line emission as a possible mechanism of X-ray lines in gamma-ray bursts

The recent discoveries of X-ray lines in the afterglows of gamma-ray bursts (GRBs) provide significant clues to the nature of GRB progenitors and central environments. However, the interpretation of iron lines as resulting from fluorescence or recombination requires a large amount of iron material. We argue that the very strong iron line could be attributed to an alternative mechanism: Cerenkov line emission, since relativistic electrons and dense medium exist near GRB sites. Therefore, broad iron lines are expected, and the line intensity will be nearly independent of the iron abundance; a medium with anomalously high Fe abundance is not required.

Simplified spectrum and power formulae for resonant inverse Compton scattering in a strong magnetic field

Abstract The resonant inverse Compton scattering (RICS) of a relativistic electron in an intense magnetic field is an important radiation mechanism in hard X-ray and γ -ray astrophysics. So far the available formulae describing RICS radiation are quite complicate in mathematics and not easy to understand in physics. In this Letter, we present the markedly simplified, analytical formulae for both the spectral and the total power of the RICS process. We will show that the RICS radiation has good monochromaticity which concentrates in hard X-ray and γ -ray wavebands, and has extremely high efficiency when compared with the coexistent, nonresonant inverse Compton scattering, if the “accommodation condition”, derived in this Letter, is satisfied.

SN 1987A: Evolution of the Envelope Temperature as Deduced from Hα Emission

In this paper, we present a new method for determining the temperature and ionization evolution of the hydrogen envelope of SN 1987A by comparing the observed H alpha light curve and one which is derived from the recombination theory for hydrogen lines, This is a simple and convenient method for determining the temperature and ionization evolution which could be applicable to the late time of all Type II supernovae.

A one-dimensional accretion column model for magnetized neutron stars☆☆☆

Abstract The infalling movement of the matter accreted onto a magnetized neutron star is discussed. A one-dimensional accretion column model is presented to describe the variations of the infalling velocity, density and temperature of the infalling plasma. The column can be divided from top down into four zones, impact, deceleration of ideal gas, deceleration of degenerate gas and outflow. As an example, the accretion column for an accretion rate of 10 17 g/s and a polar magnetic field of ≈ 10 8 T was calculated. We discuss thermonuclear reaction inside the column, and consider that it may be related to the quasi-periodic oscillation (QPO) of the X-ray flux in low-mass close binaries.

Evolution of X-ray spectra in down-Comptonization. A comparison of the extended Kompaneets equation with Monte Carlo simulation and the Ross-McCray equation

The original Kompaneets equation fails to describe down-Comptonization, which is the most important radiative transfer process in hard X-ray and γ-ray astronomy, compared with up-Comptonization. In this paper, we improve our previous derivation of the extended Kompaneets equation and present it more clearly. The new equation can be used to describe a more general Comptonization process, including up- and down-Comptonization, suitable for any case, hν � kTe, hν � kTe and hν ∼ kTe. The condition of the original Kompaneets equation hν � kTe is no longer necessary. Using the extended equation, we give some typical solutions in X-ray astronomy, and compare them with those of the prevailing Monte Carlo simulations and the Ross-McCray equation. The excellent consistency between the extended Kompaneets equation and Monte Carlo simulation or Ross-McCray equation confirms the correctness of our extended Kompaneets equation. The numerical solution of the extended Kompaneets equation is less expensive in terms of computational time than the Monte Carlo simulation. Another advantage of the equation method is the simplicity and the clarity in physics. The potential applications in X-ray and γ-ray astronomy are also emphasized.

An analysis of the X-ray emission in the late stage of SN 1987 A

Abstract Following the reasonable explanation of the evolution of the SN 1987As bolometric luminosity at the later phase by the accretion model, we suggest that the observed soft X-ray originates in the accretion of the central neutron star. Results of our model calculation are consistent with the observations. We predict that the observed X-ray flux will increase only for a certain length of time, and will begin to decrease around day 4100.

The contribution of accretion to the bolometric luminosity of SN 1987 A

The investigations of the bolometric light curve of SN1987A are briefly reviewed. We suggest that the accretion luminosity produced by an assumed neutron star in the center of SN1987A is important for the evolution of the bolometric light curve at a later stage. We emphasize the marked difference of our model with previous accretion models, where the back- fall of material mainly occurs within the first few seconds after the explosion and the details of accretion are dependent on the explosion mechanism which is very uncertain. In this paper, we are concerned with the continuous gravitational infall of mate- rial within the expansion envelope. Our suggestion is directly inspired by the observation of the line profile and is weakly dependent on the explosion model. Taking as typical values of the neutron star mass M =1 :4M and radius R =1 0 6 cm, the model calculation fits the observed light curve well. This a posteriori supports the assumption of central neutron star.