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arXiv 0901.1006astro-ph.HEastro-ph.SR
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用Chandra测量热发射孤立中子星的自行

Proper motions of thermally emitting isolated neutron stars measured with Chandra

C. Motch, A. M. Pires, F. Haberl, A. Schwope, V. E. Zavlin

摘要:

钱德拉卓越的天体测量能力提供了在这个波长范围内以前所未有的精度测量X射线源自行的可能性。我们最近完成了对ROSAT全天巡天中发现的七颗热辐射射电宁静孤立中子星(INSs)中的三颗的自行巡天。这些INS(RX J0420.0 - 5022、RX J0806.4 - 4123和RX J1308.6 + 2127)要么缺乏光学对应物,要么光学对应物太暗,以至于地面或空间光学观测将目前仪器的可能性推到了极限。每隔3至5年获得一对ACIS观测数据,以测量X射线源在X射线天空中的位移,并以河外或遥远的银河X射线源的背景作为参考。我们推导出RX J0420.0 - 5022和RX J0806.4 - 4123自行的2 σ上限分别为123 mas/yr和86 mas/yr。RX J1308.6 + 2127显示出非常显著的位移(~9 sigma),产生mu = 220 +/-25 mas/yr,在所有ROSAT发现的INS中测量的第二快。这个源可能正以一定的速度迅速远离银河平面,该速度排除了来自星际介质的任何显著的物质吸积。它的横向速度约为740(d/700 pc)km/s,可能是所有ROSAT INS中最大的,其相应的空间速度也是中子星记录中最快的。因此RX J1308.6 + 2127是一颗中年(年龄约1 My)高速冷却的中子星。我们调查其可能的起源在附近的OB协会或从一个领域OB星。在大多数情况下,从出生地开始的飞行时间明显短于从自旋下降率得出的特征年龄。ROSAT INS的横向速度分布与正常射电望远镜的横向速度分布没有统计学差异。

英文摘要:

The remarkable astrometric capabilities of Chandra offer the possibility to measure proper motions of X-ray sources with an unprecedented accuracy in this wavelength range. We recently completed a proper motion survey of three of the seven thermally emitting radio-quiet isolated neutron stars (INSs) discovered in the ROSAT all-sky survey. These INSs (RX J0420.0-5022, RX J0806.4-4123, and RX J1308.6+2127) either lack an optical counterpart or have one so faint that ground based or space born optical observations push the current possibilities of the instrumentation to the limit. Pairs of ACIS observations were acquired 3 to 5 years apart to measure the displacement of the sources on the X-ray sky using as reference the background of extragalactic or remote Galactic X-ray sources. We derive 2 sigma upper limits of 123 mas/yr and 86 mas/yr on the proper motion of RX J0420.0-5022 and RX J0806.4-4123, respectively. RX J1308.6+2127 exhibits a very significant displacement (~ 9 sigma) yielding mu = 220 +/- 25 mas/yr, the second fastest measured among all ROSAT discovered INSs. The source is probably moving away rapidly from the Galactic plane at a speed which precludes any significant accretion of matter from the interstellar medium. Its transverse velocity of ~ 740 (d/700pc) km/s might be the largest of all ROSAT INSs and its corresponding spatial velocity stands among the fastest recorded for neutron stars. RX J1308.6+2127 is thus a middle-aged (age ~ 1 My) high velocity cooling neutron star. We investigate its possible origin in nearby OB associations or from a field OB star. In most cases, the flight time from birth place appears significantly shorter than the characteristic age derived from spin down rate. The distribution in transverse velocity of ROSAT INSs is not statistically different from that of normal radio pulsars.

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