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arXiv 1604.04400astro-ph.HE
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低质量X射线双星软态的硬尾辐射及其与中子星磁场的关系

Hard-tail emission in the soft state of low-mass X-ray binaries and their relation to the neutron star magnetic field

Kazumi Asai, Tatehiro Mihara, Masaru Mastuoka, Mutsumi Sugizaki

摘要:

利用MAXI/GSC和Swift/BAT的光变曲线研究了9颗明亮的环礁低质量中子星双星(NS-LMXB)在软态下的平均硬尾X射线辐射。两个源(4U 1820 $-$ 30和4U 1735 $-$ 44)表现出大的硬度比(15- 50 keV $/$ 2- 10 keV:{ \it HR} $>$ 0.1),而其它源分布在{ \it HR} $\ltsim$ 0.1。在任何一种情况下,{ \it HR}都不依赖于2- 10 keV的光度。因此,{ \it HR}的差异是由于15- 50 keV的光度,这是康普顿化的发射。康普顿云被认为是围绕着中子星的。康普顿云的大小会影响{ \it HR}的值。虽然NS-LMXB的磁场很弱,但我们可以预期它的阿尔文半径比最里面的稳定圆形轨道或某些源中的中子星半径更大。在这种情况下,吸积流入停止在阿尔芬半径,并会产生相对较大的康普顿云。这将导致观察到更大的康普顿化发射。通过将康普顿云的大小差异归因于阿尔文半径,我们可以估算出中子星的磁场。得到的下限/上限与以前的结果一致。

英文摘要:

Average hard-tail X-ray emission in the soft state of nine bright Atoll low-mass X-ray binaries containing a neutron star (NS-LMXBs) are investigated by using the light curves of MAXI/GSC and Swift/BAT. Two sources (4U 1820$-$30 and 4U 1735$-$44) exhibit large hardness ratio (15--50 keV$/$2--10 keV: {\it HR} $>$ 0.1), while the other sources distribute at {\it HR} $\ltsim$ 0.1. In either case, {\it HR} does not depend on the 2--10 keV luminosity. Therefore the difference of {\it HR} is due to the 15--50 keV luminosity, which is Comptonized emission. The Compton cloud is assumed to be around the neutron star. The size of the Compton cloud would affect the value of {\it HR}. Although the magnetic field of NS-LMXB is weak, we could expect a larger Alfvén radius than the innermost stable circular orbit or the neutron star radius in some sources. In such cases, the accretion inflow is stopped at the Alfvén radius and would create relatively large Compton cloud. It would result in the observed larger Comptonized emission. By attributing the difference of the size of Compton cloud to the Alfvén radius, we can estimate the magnetic fields of neutron star. The obtained lower/upper limits are consistent with the previous results.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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