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arXiv 0708.0002astro-ph
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1E 1547.0 - 5408:一颗自转周期为2秒的射电磁星

1E 1547.0-5408: a radio-emitting magnetar with a rotation period of 2 seconds

F. Camilo, S. M. Ransom, J. P. Halpern, J. Reynolds

摘要:

可变X射线源1E 1547.0 - 5408被Gelfand和Gaensler(2007)确认为G327.24 - 0.13中的一颗可能的磁星,这是一颗明显的超新星遗迹。利用帕克斯射电望远镜,我们发现了周期为P = 2.069 s的脉动。使用澳大利亚望远镜紧凑阵列,我们将它们定位到1E 1547.0 - 5408。我们测得dP/dt =(2.318 ± 0.005)e-11,对于在真空中旋转的磁偶极子,给出表面场强为2.2e~(14)G,特征年龄为1.4kyr,自旋下降光度为1.0e~(35)ergs/s。连同它的X射线特征,1E 1547.0 - 5408的这些旋转参数证明它是一颗磁星,只有第二颗已知发射无线电波的磁星。距离约为9千秒差距,来自830秒差距/立方厘米的分散测量。由于ISM中的多径传播,1.4GHz频率下的脉冲轮廓非常宽且不对称,其结果是1.4GHz下的总通量仅约75%是脉冲的。在更高的频率下,轮廓更对称并且具有FWHM = 0.12P。与普通的射电磁星不同,但与其他已知的无线电发射磁星XTE J1810 - 197一样,1.4 - 6.6 GHz的频谱是平坦的或上升的,我们观察到脉冲形状的巨大突然变化。在同一时期的雨燕X射线观测中,1E 1547.0 - 5408以创纪录的高通量被探测到,f_X(1 - 8 keV)~5e-12 ergs/cm^2/s,是历史最低值的16倍。这颗脉冲星在1998年的无线电观测档案中没有被发现,这意味着它的通量小于目前水平的0.2倍。结合XTE J1810 - 197的瞬态行为,这些结果表明射电辐射是由通常静止的磁星的X射线爆发触发的。

英文摘要:

The variable X-ray source 1E 1547.0-5408 was identified by Gelfand & Gaensler (2007) as a likely magnetar in G327.24-0.13, an apparent supernova remnant. No X-ray pulsations have been detected from it. Using the Parkes radio telescope, we discovered pulsations with period P = 2.069 s. Using the Australia Telescope Compact Array, we localized these to 1E 1547.0-5408. We measure dP/dt = (2.318+-0.005)e-11, which for a magnetic dipole rotating in vacuo gives a surface field strength of 2.2e14 G, a characteristic age of 1.4 kyr, and a spin-down luminosity of 1.0e35 ergs/s. Together with its X-ray characteristics, these rotational parameters of 1E 1547.0-5408 prove that it is a magnetar, only the second known to emit radio waves. The distance is ~9 kpc, derived from the dispersion measure of 830 pc/cc. The pulse profile at a frequency of 1.4 GHz is extremely broad and asymmetric due to multipath propagation in the ISM, as a result of which only approximately 75% of the total flux at 1.4 GHz is pulsed. At higher frequencies the profile is more symmetric and has FWHM = 0.12P. Unlike in normal radio pulsars, but in common with the other known radio-emitting magnetar, XTE J1810-197, the spectrum over 1.4-6.6 GHz is flat or rising, and we observe large, sudden changes in the pulse shape. In a contemporaneous Swift X-ray observation, 1E 1547.0-5408 was detected with record high flux, f_X(1-8 keV) ~ 5e-12 ergs/cm^2/s, 16 times the historic minimum. The pulsar was undetected in archival radio observations from 1998, implying a flux < 0.2 times the present level. Together with the transient behavior of XTE J1810-197, these results suggest that radio emission is triggered by X-ray outbursts of usually quiescent magnetars.

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