A broad absorption feature in the X-ray spectrum of the isolated neutron star RBS1223 (1RXSJ130848.6+212708)
A broad absorption feature in the X-ray spectrum of the isolated neutron star RBS1223 (1RXSJ130848.6+212708)
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孤立中子星 RBS1223 (1RXSJ130848.6 212708) 的 X 射线光谱中具有广泛的吸收特征
DOI：
10.1051/0004-6361:20030450
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发表时间：
2003
影响因子：
6.5
通讯作者：
C. Motch
中科院分区：
文献类型：
--
作者：
F. Haberl;A. Schwope;V. Hambaryan;G. Hasinger;C. Motch
在2001年12月和2003年1月，用XMM-牛顿号上的仪器获得了孤立中子星星RBS 1223的X射线光谱，显示出在低于500 eV的能量下偏离普朗克能量分布。当将σ = 100 eV且以300 eV能量为中心的宽的高斯形吸收线添加到吸收黑体模型时，光谱很好地拟合。得到的等效线宽为−150 eV。然而，EPIC探测器在这些低能量下的光谱分辨率以及RGS仪器的较低统计质量和受限能带不足以排除能量低至100 eV的更宽谱线或几条未分辨谱线。对吸收特征最可能的解释是质子在中子星星的磁场中产生的回旋吸收线。在这幅图中，对于具有正则质量和半径的中子星星，100-300 eV的线能量产生2-6 × 10 13 G的磁场强度。在10.31 s的周期，这意味着一个双峰脉冲轮廓，从不同的能带折叠光曲线，显示出不同的硬度比的两个峰。这证实了RBS 1223的真实自旋周期是最初认为的两倍长，并表明回旋吸收随脉冲相位的变化。我们还提出，在Cropper等人（2001）的RX J0720.4−3125相位分辨光谱中看到的光电吸收变化，当正式与吸收黑体模型拟合时，是由随脉冲相位变化的回旋吸收引起的。
X-ray spectra of the isolated neutron star RBS1223 obtained with the instruments on board XMM-Newton in December 2001 and January 2003 show deviations from a Planckian energy distribution at energies below 500 eV. The spectra are well fit when a broad, Gaussian-shaped absorption line with σ = 100 eV and centered at an energy of 300 eV is added to an absorbed blackbody model. The resulting equivalent width of the line is −150 eV. However, the spectral resolution at these low energies of the EPIC detectors and the lower statistical quality and restricted energy band of the RGS instruments are not sufficient to exclude even broader lines at energies down to 100 eV or several unresolved lines. The most likely interpretation of the absorption feature is a cyclotron absorption line produced by protons in the magnetic field of the neutron star. In this picture line energies of 100-300 eV yield a magnetic field strength of 2-6 × 10 13 G for a neutron star with canonical mass and radius. Folding light curves from different energy bands at a period of 10.31 s, which implies a double peaked pulse profile, shows different hardness ratios for the two peaks. This confirms that the true spin period of RBS1223 is twice as long as origi- nally thought and suggests variations in cyclotron absorption with pulse phase. We also propose that changes in photo-electric absorption seen in phase resolved spectra of RX J0720.4−3125 by Cropper et al. (2001), when formally fit with an absorbed blackbody model, are caused instead by cyclotron absorption varying with pulse phase.