星期二, 十一月 21, 2006
星期一, 十一月 20, 2006
Pavlov2005 强磁场中的一价氦原子
计算了强磁场中的一价氦原子的能级。
这篇文章至少说明结合天文背景的原子能谱计算还有大量可以做的工作。
The Astrophysical Journal, 635:L61–L64, 2005 December 10
ONCE-IONIZED HELIUM IN SUPERSTRONG MAGNETIC FIELDS
George G. Pavlov1 and Victor G. Bezchastnov2,3
Received 2005 April 15; accepted 2005 November 1; published 2005 November 30
ABSTRACT
It is generally believed that magnetic fields of some neutron stars, the so-called magnetars, are enormously strong,
up to 1014–1015 G. Recent investigations have shown that the atmospheres of magnetars are possibly composed of
helium. We calculate the structure and bound-bound radiative transitions of the He ion in superstrong fields,
including the effects caused by the coupling of the ion’s internal degrees of freedom to its center-of-mass motion.
We show that He in superstrong magnetic fields can produce spectral lines with energies of up to ≈3 keV, and it
may be responsible for absorption features detected recently in the soft X-ray spectra of several radio-quiet isolated
neutron stars. Quantization of the ion’s motion across a magnetic field results in a fine structure of spectral lines,
with a typical spacing of tens of electron volts in magnetar-scale fields. It also gives rise to ion cyclotron transitions,
whose energies and oscillator strengths depend on the state of the bound ion. The bound-ion cyclotron lines of He
can be observed in the UV-optical range at G, and they get into the soft X-ray B 1013 range at B 1014 G.
Subject headings: atomic processes—line: formation—stars: individual (1E 1207.45209)—
stars: magnetic fields—stars: neutron—X-rays: stars
这篇文章至少说明结合天文背景的原子能谱计算还有大量可以做的工作。
The Astrophysical Journal, 635:L61–L64, 2005 December 10
ONCE-IONIZED HELIUM IN SUPERSTRONG MAGNETIC FIELDS
George G. Pavlov1 and Victor G. Bezchastnov2,3
Received 2005 April 15; accepted 2005 November 1; published 2005 November 30
ABSTRACT
It is generally believed that magnetic fields of some neutron stars, the so-called magnetars, are enormously strong,
up to 1014–1015 G. Recent investigations have shown that the atmospheres of magnetars are possibly composed of
helium. We calculate the structure and bound-bound radiative transitions of the He ion in superstrong fields,
including the effects caused by the coupling of the ion’s internal degrees of freedom to its center-of-mass motion.
We show that He in superstrong magnetic fields can produce spectral lines with energies of up to ≈3 keV, and it
may be responsible for absorption features detected recently in the soft X-ray spectra of several radio-quiet isolated
neutron stars. Quantization of the ion’s motion across a magnetic field results in a fine structure of spectral lines,
with a typical spacing of tens of electron volts in magnetar-scale fields. It also gives rise to ion cyclotron transitions,
whose energies and oscillator strengths depend on the state of the bound ion. The bound-ion cyclotron lines of He
can be observed in the UV-optical range at G, and they get into the soft X-ray B 1013 range at B 1014 G.
Subject headings: atomic processes—line: formation—stars: individual (1E 1207.45209)—
stars: magnetic fields—stars: neutron—X-rays: stars
Bhattacharyya2006 中子星表面原子谱线的形状
中子星表面的原子谱线不仅要受到磁场的影响，还会受到因旋转导致的多普勒效应，还有狭义和广义相对论效应。对于弱磁场的种子星，磁场的影响甚至 可以忽略。
The Astrophysical Journal, 644:1085–1089, 2006 June 20
THE SHAPES OF ATOMIC LINES FROM THE SURFACES
OF WEAKLY MAGNETIC ROTATING NEUTRON STARS AND THEIR IMPLICATIONS
Sudip Bhattacharyya,1 M. Coleman Miller,1, 2 and Frederick K. Lamb3, 4
Received 2004 December 6; accepted 2006 March 3
ABSTRACT
Motivated by the report by Cottam et al. of iron resonance scattering lines in the spectra of thermonuclear bursts
from EXO 0748676, we have investigated the information about neutron star structure and the geometry of the
emission region that can be obtained by analyzing the profiles of atomic lines formed at the surface of the star. We
have calculated the detailed profiles of such lines, taking into account the star’s spin and the full effects of special and
general relativity, including light bending and frame dragging. We discuss the line shapes produced by rotational
Doppler broadening and magnetic splitting of atomic lines for the spin rates and magnetic fields expected in neutron
stars in low-mass X-ray binary systems.We show that narrow lines are possible even for rapidly spinning stars if the
emission region or the line of sight are close to the spin axis. For most neutron stars in low-mass systems, magnetic
splitting is too small to obscure the effects of special and general relativity.We show that the ratio of the star’s mass to
its equatorial radius can be determined to within 5% using atomic line profiles, even if the lines are broad and skewed.
This is the precision required to constrain strongly the equation of state of neutron star matter.We show further that if
the radius and latitude of emission are known to 5%–10% accuracy, then frame dragging has a potentially detectable
effect on the profiles of atomic lines formed at the stellar surface.
Subject headinggs: equation of state — line: profiles — relativity — stars: neutron — stars: rotation —
X-rays: stars
The Astrophysical Journal, 644:1085–1089, 2006 June 20
THE SHAPES OF ATOMIC LINES FROM THE SURFACES
OF WEAKLY MAGNETIC ROTATING NEUTRON STARS AND THEIR IMPLICATIONS
Sudip Bhattacharyya,1 M. Coleman Miller,1, 2 and Frederick K. Lamb3, 4
Received 2004 December 6; accepted 2006 March 3
ABSTRACT
Motivated by the report by Cottam et al. of iron resonance scattering lines in the spectra of thermonuclear bursts
from EXO 0748676, we have investigated the information about neutron star structure and the geometry of the
emission region that can be obtained by analyzing the profiles of atomic lines formed at the surface of the star. We
have calculated the detailed profiles of such lines, taking into account the star’s spin and the full effects of special and
general relativity, including light bending and frame dragging. We discuss the line shapes produced by rotational
Doppler broadening and magnetic splitting of atomic lines for the spin rates and magnetic fields expected in neutron
stars in low-mass X-ray binary systems.We show that narrow lines are possible even for rapidly spinning stars if the
emission region or the line of sight are close to the spin axis. For most neutron stars in low-mass systems, magnetic
splitting is too small to obscure the effects of special and general relativity.We show that the ratio of the star’s mass to
its equatorial radius can be determined to within 5% using atomic line profiles, even if the lines are broad and skewed.
This is the precision required to constrain strongly the equation of state of neutron star matter.We show further that if
the radius and latitude of emission are known to 5%–10% accuracy, then frame dragging has a potentially detectable
effect on the profiles of atomic lines formed at the stellar surface.
Subject headinggs: equation of state — line: profiles — relativity — stars: neutron — stars: rotation —
X-rays: stars
Sanwal2002 孤立中子星1E 1207.4－5209的X射线谱
1E 1207.4－5209是超新星遗迹PKS 1209－51/52中的一颗孤立中子星，文章给了Chandra对它X射线的谱的观测。在0.7和1.4keV上有明显的吸收。一个可能的解释是一价氦原子在强磁场中的跃迁。
The Astrophysical Journal, 574:L61–L64, 2002 July 20
DISCOVERY OF ABSORPTION FEATURES IN THE X-RAY SPECTRUM OF AN ISOLATED NEUTRON STAR
D. Sanwal,1 G. G. Pavlov,1 V. E. Zavlin,2 and M. A. Teter1
Received 2002 April 19; accepted 2002 June 17; published 2002 June 24
ABSTRACT
We observed 1E 1207.45209, a neutron star in the center of the supernova remnant PKS 120951/52, with
the ACIS detector aboard the Chandra X-Ray Observatory and detected two absorption features in the source
spectrum. The features are centered near 0.7 and 1.4 keV; their equivalent widths are about 0.1 keV. We discuss
various possible interpretations of the absorption features and exclude some of them. A likely interpretation is
that the features are associated with atomic transitions of once-ionized helium in the neutron star atmosphere
with a strong magnetic field. The first clear detection of absorption features in the spectrum of an isolated neutron
star provides an opportunity to measure the mass-to-radius ratio and to constrain the equation of state of the
superdense matter.
Subject headings: pulsars: individual (1E 1207.45209)—stars: neutron—
supernovae: individual (PKS 120951/52)—X-rays: stars
The Astrophysical Journal, 574:L61–L64, 2002 July 20
DISCOVERY OF ABSORPTION FEATURES IN THE X-RAY SPECTRUM OF AN ISOLATED NEUTRON STAR
D. Sanwal,1 G. G. Pavlov,1 V. E. Zavlin,2 and M. A. Teter1
Received 2002 April 19; accepted 2002 June 17; published 2002 June 24
ABSTRACT
We observed 1E 1207.45209, a neutron star in the center of the supernova remnant PKS 120951/52, with
the ACIS detector aboard the Chandra X-Ray Observatory and detected two absorption features in the source
spectrum. The features are centered near 0.7 and 1.4 keV; their equivalent widths are about 0.1 keV. We discuss
various possible interpretations of the absorption features and exclude some of them. A likely interpretation is
that the features are associated with atomic transitions of once-ionized helium in the neutron star atmosphere
with a strong magnetic field. The first clear detection of absorption features in the spectrum of an isolated neutron
star provides an opportunity to measure the mass-to-radius ratio and to constrain the equation of state of the
superdense matter.
Subject headings: pulsars: individual (1E 1207.45209)—stars: neutron—
supernovae: individual (PKS 120951/52)—X-rays: stars
Cottam2006 中子星中引力红移后的谱
文章对X射线双星EXO 0748-676的X射线暴做了观测，辨认出了一些铁线，发现引力红移值在0.35.
Comments: Published in Nature (Nov 7, 2002)
Journal-ref: Nature 420 (2002) 51-54
Gravitationally redshifted absorption lines in the X-ray burst spectra of a neutron star
Authors: J. Cottam (1), F. Paerels (2), M. Mendez (3) ((1) NASA/GSFC, (2) Columbia, (3) SNON)Comments: Published in Nature (Nov 7, 2002)
Journal-ref: Nature 420 (2002) 51-54
The fundamental properties of neutron stars provide a direct test of the equation of state of cold nuclear matter, a relationship between pressure and density that is determined by the physics of the strong interactions between the particles that constitute the star. The most straightforward method of determining these properties is by measuring the gravitational redshift of spectral lines produced in the neutron star photosphere. The equation of state implies a mass-radius relation, while a measurement of the gravitational redshift at the surface of a neutron star provides a direct constraint on the mass-to-radius ratio. Here we report the discovery of signficant absorption lines in the spectra of 28 bursts of the low-mass X-ray binary EXO 0748-676. We identify the most signficant features with the Fe XXVI and XXV n=2-3 and O VIII n=1-2 transitions, all with a redshift of z=0.35, identical within small uncertainties for the respective transitions. For an astrophysically plausible range of masses (M ~ 1.3-2.0 M_solar), this value is completely consistent with models of neutron stars composed of normal nuclear matter, while it excludes some models in which the neutron stars are made of more exotic matter.
Burwitz2002 孤立中子星RX J1856.5-3754的热谱观测
由Chamdra和XMM－Newton观测。此文是反面的，认为辐射可以用两个黑体成分拟合，而不是强磁场中的原子谱。
The thermal radiation of the isolated neutron star RX J1856.5-3754 observed with Chandra and XMM-Newton
Authors: V. Burwitz, F. Haberl, R. Neuhaeuser, P. Predehl, J. Truemper, V.E. Zavlin (Max-Planck-Institut fuer extraterrestrische Physik (MPE Garching))Comments: 6 pages, (including 3 figures) accepted for publication in Astronomy and Astrophysics (A&A)
Journal-ref: Astron.Astrophys. 399 (2003) 1109-1114
We present results of the analysis of data collected in 57-ks XMM-Newton and 505-ks Chandra observations of the nearby ~= 120 pc isolated neutron star RX J1856.5-3754. We confirm most of the statements made by Burwitz et al. (2001) who discussed the original 55-ks Chandra data. Detailed spectral analysis of the combined X-ray and optical data rules out the currently available nonmagnetic light and heavy element neutron star atmosphere (LTE) models with hydrogen, helium, iron and solar compositions. We find that strongly magnetized atmosphere models also are unable to represent the data. The X-ray and optical data show no spectral features and are best fitted with a two-component blackbody model with kT_{bb,X}^{\infty} ~= 63.5 eV and R_{bb,X}^{\infty} ~= 4.4(d/120 pc) km for the hot X-ray emitting region, and kT_{bb,opt}^{\infty}<33>17(d/120 pc) km for the rest of the neutron star surface responsible for the optical flux. The large number of counts collected with XMM-Newton allows us to reduce the upper limit on periodic variation in the X-ray range down to 1.3% (at a 2\sigma confidence level) in the 10^{-3}-50 Hz frequency range. In an attempt to explain this small variability, we discuss an one-component model with kT_{bb}^{\infty} ~= 63 eV and R_{bb}^{\infty} ~= 12.3(d/120 pc) km. This model requires a low radiative efficiency in the X-ray domain, which may be expected if the neutron star has a condensed matter surface.
星期五, 十一月 10, 2006
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