Observations of the Crab Nebula and Its Pulsar in the Far-Ultraviolet and in the Optical
Observations of the Crab Nebula and Its Pulsar in the Far-Ultraviolet and in the Optical
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DOI：
10.1086/309062
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发表时间：
2000-02
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影响因子：
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通讯作者：
J. Sollerman;P. Lundqvist;D. Lindler;R. Chevalier;C. Fransson;T. Gull;C. Pun;G. Sonneborn
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文献类型：
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作者：
J. Sollerman;P. Lundqvist;D. Lindler;R. Chevalier;C. Fransson;T. Gull;C. Pun;G. Sonneborn
我们介绍了用哈勃太空望远镜上的空间望远镜成像光谱仪对蟹状星云及其脉冲星进行的远紫外观测。在C IVλ1550中可以看到星云中产生的宽广的蓝移吸收，达到了大约2500公里的蓝风速度S-1。这可以解释为蟹状星云周围有一个快速外壳的证据，我们采用了球对称模型来约束这样一个外壳的性质。从线条轮廓我们发现，在贝壳中密度似乎向外减小。壳层质量的一个可能下限是~0.3M☉，伴随动能为~1.5×1049ergs。不能排除1051ergs的快速大质量壳，但如果密度剖面比ρ(R)∝R-4陡峭得多，并且最大速度为≲6000公里S-1，则不太可能。观测覆盖了1140-1720ä区域，与之前获得的脉冲星相比，该区域更深入于紫外线。利用光谱仪的时间标签模式，我们得到了该光谱区的脉冲分布。虽然主峰略窄，但轮廓与我们以前在近紫外区获得的相似。连同近紫外线数据和北欧光学望远镜的新光学数据，我们的Crab脉冲星光谱覆盖了从1140到9250ä的整个区域。用标准消光曲线对光谱进行消光处理，得到了变红参数E(B-V)=0.52，R=3.1的平坦光谱。蟹状脉冲星的去简并光谱可用指数αν=0.11±0.04的幂函数来拟合。确定光谱指数的主要不确定性是星际变红的数量和特征，我们已经研究了αν与E(B-V)和R的依赖关系。在我们25‘’×0的扩展发射中，我们在远紫外狭缝中探测到了蟹状星云的C IVλ1550和He IIλ1640发射线。沿着脉冲星的视线探测到几条星际吸收线。Lyα吸收谱显示中性氢气的柱密度为(3.0±0.5)×10 2 1 cm-2，这与我们估算的E(B-V)=0.5 2mag符合得很好。其他谱线没有证据表明原子气体中的金属严重枯竭。
We present far-UV observations of the Crab Nebula and its pulsar made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Broad, blueshifted absorption arising in the nebula is seen in C IV λ1550, reaching a blueward velocity of ~2500 km s-1. This can be interpreted as evidence for a fast outer shell surrounding the Crab Nebula, and we adopt a spherically symmetric model to constrain the properties of such a shell. From the line profile we find that the density appears to decrease outward in the shell. A likely lower limit to the shell mass is ~0.3 M☉ with an accompanying kinetic energy of ~1.5 × 1049 ergs. A fast massive shell with 1051 ergs cannot be excluded but is less likely if the density profile is much steeper than ρ(R) ∝ R-4 and the maximum velocity is ≲6000 km s-1. The observations cover the region 1140-1720 Å, which is further into the ultraviolet than has previously been obtained for the pulsar. With the time-tag mode of the spectrograph we obtain the pulse profile in this spectral regime. The profile is similar to that previously obtained by us in the near-UV, although the primary peak is marginally narrower. Together with the near-UV data, and new optical data from the Nordic Optical Telescope, our spectrum of the Crab pulsar covers the entire region from 1140 to 9250 Å. Dereddening the spectrum with a standard extinction curve we achieve a flat spectrum for the reddening parameters E(B-V) = 0.52, R = 3.1. This dereddened spectrum of the Crab pulsar can be fitted by a power law with spectral index αν = 0.11 ± 0.04. The main uncertainty in determining the spectral index is the amount and characteristics of the interstellar reddening, and we have investigated the dependence of αν on E(B-V) and R. In the extended emission covered by our 25′′ × 0.″5 slit in the far-UV, we detect C IV λ1550 and He II λ1640 emission lines from the Crab Nebula. Several interstellar absorption lines are detected along the line of sight to the pulsar. The Lyα absorption indicates a column density of (3.0 ± 0.5) × 1021 cm-2 of neutral hydrogen, which agrees well with our estimate of E(B-V) = 0.52 mag. Other lines show no evidence of severe depletion of metals in atomic gas.