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arXiv 0705.4095astro-ph
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磁星XTE J1810-197的可变射电-X射线能谱

The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197

F. Camilo, S. M. Ransom, J. Penalver, A. Karastergiou, M. H. van Kerkwijk, M. Durant, J. P. Halpern, J. Reynolds, C. Thum, D. J. Helfand, N. Zimmerman, I. Cognard

备注：
Accepted for publication in ApJ; contains improved discussion of infrared uncertainties
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摘要：

我们对5.54 s反常X射线脉冲星XTE J1810-197进行了射电、毫米波和红外波段的观测，目的是了解它的宽波段光谱。在IRAM 30米望远镜上，我们探测到了88和144 GHz的磁星，这是脉冲星有史以来最高的射频发射。在88 GHz处，我们检测到许多单个脉冲，典型宽度约为2 ms，峰值通量密度高达45 Jy。结合帕克斯望远镜、南凯望远镜和格林班克望远镜几乎同时观测到的数据，我们发现在2006年7月下旬，脉冲星的光谱指数在1.4- 144 GHz范围内为-0.5<alpha<0。2006年5月至9月间，九个双频甚大阵列和澳大利亚望远镜紧凑阵列的观测结果与这一发现一致，同时显示出α随时间的变化。我们从IRAM观测中推断，XTE J1810-197在毫米波长处保持高度线性偏振。此外，朝向该脉冲星，星际介质中强散射和弱散射之间的跃迁频率可能接近50 GHz。在双子座，我们在2006年9月探测到了2.2um的脉冲星，在迄今为止观测到的最暗的水平，K_s=21.89+-0.15。我们还分析了四个存档的红外甚大望远镜观测（两个未发表），发现亮度在3年的时间跨度内波动在2-3倍之内，不像X射线通量的单调衰减。因此，红外线和X射线通量之间没有相关性，并且仍然不确定红外线和无线电通量之间是否存在任何相关性。

英文摘要：

We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio, millimeter, and infrared (IR) wavelengths, with the aim of learning about its broad-band spectrum. At the IRAM 30m telescope, we have detected the magnetar at 88 and 144GHz, the highest radio-frequency emission ever seen from a pulsar. At 88GHz we detected numerous individual pulses, with typical widths ~2ms and peak flux densities up to 45Jy. Together with nearly contemporaneous observations with the Parkes, Nancay, and Green Bank telescopes, we find that in late 2006 July the spectral index of the pulsar was -0.5<alpha<0 over the range 1.4-144GHz. Nine dual-frequency Very Large Array and Australia Telescope Compact Array observations in 2006 May-September are consistent with this finding, while showing variability of alpha with time. We infer from the IRAM observations that XTE J1810-197 remains highly linearly polarized at millimeter wavelengths. Also, toward this pulsar, the transition frequency between strong and weak scattering in the interstellar medium may be near 50GHz. At Gemini, we detected the pulsar at 2.2um in 2006 September, at the faintest level yet observed, K_s=21.89+-0.15. We have also analyzed four archival IR Very Large Telescope observations (two unpublished), finding that the brightness fluctuated within a factor of 2-3 over a span of 3 years, unlike the monotonic decay of the X-ray flux. Thus, there is no correlation between IR and X-ray flux, and it remains uncertain whether there is any correlation between IR and radio flux.

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