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arXiv 0704.2079astro-ph
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行星脉冲星B1257 +12的X射线辐射

X-ray emission from the planet pulsar B1257+12

G. G. Pavlov, O. Kargaltsev, G. P. Garmire, A. Wolszczan

摘要:

本文报道了钱德拉X射线天文台对毫秒脉冲星B1257+12的探测。在20 ks曝光中,我们探测到来自脉冲星的25个光子,能量在0.4和2.0 keV之间,对应于该能量范围内的通量F_X=(4.4+/- 0.9)*10^{-15} ergs ^{-1} cm^{-2}。X射线谱可用幂律模型描述,在0.3- 8 keV波段,光子指数Gamma = 2.8,光度L_X \approx = 2.5*10^{29}尔格·s^{-1},合理距离为500 pc,氢柱密度N_H=3*10^{20} cm^{-2}。或者,光谱可以用黑体模型拟合,kT约为0.22 keV,投影发射面积约为2000 m^2。如果热X射线是从两个对称的极冠中发射的,则两个极冠的辐射热光度为2 L_bol ~ 3*10^{29} ergs ^{-1}。我们将所得结果与其它30颗毫秒级双星的X射线观测数据进行了比较,发现PSR B 1257 +12的表观X射线效率(L_X/Edot ~ 3*10^{-5},d=500 pc)低于大多数毫秒级双星。如果辐射是磁层的,这可能是由于X射线脉冲星光束的不利方向,或者如果辐射是热的,这可能是由于极帽的强烈不对称性(例如,其中一个极冠比另一个亮得多,在脉冲星周期的大部分时间里都是不可见的)。另一种解释是,它可能是由于脉冲星周围物质吸收了X射线,例如脉冲星周围行星系统形成后留下的耀斑碎片盘。

英文摘要:

We report the detection of the millisecond pulsar B1257+12 with the Chandra X-ray Observatory. In a 20 ks exposure we detected 25 photons from the pulsar, with energies between 0.4 and 2.0 keV, corresponding to the flux F_X=(4.4+/- 0.9)*10^{-15} ergs s^{-1} cm^{-2} in this energy range. The X-ray spectrum can be described by a power-law model with photon index Gamma = 2.8 and luminosity L_X \approx 2.5*10^{29} ergs s^{-1} in the 0.3--8 keV band, for a plausible distance of 500 pc and hydrogen column density N_H=3*10^{20} cm^{-2}. Alternatively, the spectrum can be fitted by a blackbody model with kT ~ 0.22 keV and projected emitting area ~2000 m^2. If the thermal X-rays are emitted from two symmetric polar caps, the bolometric luminosity of the two caps is 2 L_bol ~ 3*10^{29} ergs s^{-1}. We compared our results with the data on other 30 millisecond pulsars observed in X-rays and found that the apparent X-ray efficiency of PSR B1257+12, L_X/Edot ~ 3*10^{-5} for d=500 pc, is lower than those of most of millisecond pulsars. This might be explained by an unfavorable orientation of the X-ray pulsar beam if the radiation is magnetospheric, or by strong asymmetry of polar caps if the radiation is thermal (e.g., one of the polar caps is much brighter than the other and remains invisible for most part of the pulsar period). Alternatively, it could be attributed to absorption of X-rays in circumpulsar matter, such as a flaring debris disk left over after formation of the planetary system around the pulsar.

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