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arXiv 1503.01307astro-ph.HE
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银河系中心磁星SGR J1745-2900头1.5年的X射线爆发

The X-ray outburst of the Galactic Centre magnetar SGR J1745-2900 during the first 1.5 year

F. Coti Zelati, N. Rea, A. Papitto, D. Viganò, J. A. Pons, R. Turolla, P. Esposito, D. Haggard, F. K. Baganoff, G. Ponti, G. L. Israel, S. Campana, D. F. Torres… 展开作者

F. Coti Zelati, N. Rea, A. Papitto, D. Viganò, J. A. Pons, R. Turolla, P. Esposito, D. Haggard, F. K. Baganoff, G. Ponti, G. L. Israel, S. Campana, D. F. Torres, A. Tiengo, S. Mereghetti, R. Perna, S. Zane, R. P. Mignani, A. Possenti, L. Stella

摘要:

2013年4月,一颗新的磁星SGR 1745-2900在进入爆发时被发现,距离银河系中心人马座A* 的超大质量黑洞只有2.4角秒的角距离。SGR 1745-2900的表面偶极磁场约为2 × 10 ^{14} G,是迄今观测到的最接近黑洞的中子星。在射电和X射线波段都探测到了这个新的辐射源,其峰值X射线光度L_X ~ 5 × 10 ^{35} erg·s^{-1}。在这里,我们报告了从2013年4月爆发开始到2014年9月SGR 1745-2900的长期钱德拉(25次观测)和XMM-牛顿(8次观测)X射线监测活动。这个前所未有的数据集使我们能够细化的源的定时特性,以及研究作为时间和旋转相位的函数的爆发光谱演化。我们的时间分析证实了自旋周期导数在2013年6月左右增加了约2倍,并显示在2013年10月30日至2014年2月21日之间进一步增加。我们发现,在1.5年内,周期导数从6.6 × 10 ^{-12} s^{-1}变化到3.3 × 10 ^{-11} s^{-1}。另一方面,与其他磁星相比,这颗磁星显示出缓慢的通量衰减和相当低效的表面冷却。特别是,星震引起的地壳冷却模型很难单独解释其爆发的前200天的高亮度源,和额外的加热的恒星表面从电流流动在扭曲的磁束可能在爆发的演变中发挥了重要作用。

英文摘要:

In 2013 April a new magnetar, SGR 1745-2900, was discovered as it entered an outburst, at only 2.4 arcsec angular distance from the supermassive black hole at the Centre of the Milky Way, Sagittarius A*. SGR 1745-2900 has a surface dipolar magnetic field of ~ 2x10^{14} G, and it is the neutron star closest to a black hole ever observed. The new source was detected both in the radio and X-ray bands, with a peak X-ray luminosity L_X ~ 5x10^{35} erg s^{-1}. Here we report on the long-term Chandra (25 observations) and XMM-Newton (8 observations) X-ray monitoring campaign of SGR 1745-2900, from the onset of the outburst in April 2013 until September 2014. This unprecedented dataset allows us to refine the timing properties of the source, as well as to study the outburst spectral evolution as a function of time and rotational phase. Our timing analysis confirms the increase in the spin period derivative by a factor of ~2 around June 2013, and reveals that a further increase occurred between 2013 Oct 30 and 2014 Feb 21. We find that the period derivative changed from 6.6x10^{-12} s s^{-1} to 3.3x10^{-11} s s^{-1} in 1.5 yr. On the other hand, this magnetar shows a slow flux decay compared to other magnetars and a rather inefficient surface cooling. In particular, starquake-induced crustal cooling models alone have difficulty in explaining the high luminosity of the source for the first ~200 days of its outburst, and additional heating of the star surface from currents flowing in a twisted magnetic bundle is probably playing an important role in the outburst evolution.

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