瞬变射电磁星1 E 1547.0-5408的VLT/NACO近红外观测
VLT/NACO near-infrared observations of the transient radio magnetar 1E 1547.0-5408
摘要：
尽管经过了大约十年的观测，人们对软伽马射线中继器（SGR）和异常X射线脉冲星（AXP）的光学和红外（IR）发射特性以及驱动它们在这些波长发射的物理过程知之甚少。这主要是由于到目前为止所实现的识别数量有限，总共五个，以及从多波段光学/红外测光获得的稀疏光谱覆盖范围。这项工作的目的是寻找一个可能的候选对手，最近发现的瞬态无线电AXP 1 E 1547.0-5408。我们进行了第一次深近红外（NIR）观测（Ks波段）的1 E 1547.0-5408与VLT在三个晚上（7月8日，12日和8月17日），在X射线源重新亮化后，并在随后的衰变报告在2007年6月左右。我们在1 E 1547.0-5408的3sigma射电位置内或附近探测到四个天体。其中最暗的天体（天体1）亮度K = 20.27 +/- 0.05，这将产生1 E 1547.0-5408的未吸收X射线与近红外线通量比FX/FK ~ 800，即平均低于其他磁星得出的值。在7月8日和8月17日的夜晚没有检测到物体1，这只允许我们将其NIR变化的上限设置为Delta Ks ~ 0.2，这阻止了我们搜索与无线电或X射线通量的相关性。我们在射电位置没有检测到其他物体，在我们最深的VLT图像（7月12日）中计算出的极限Ks ~ 21.7（在5sigma）。根据我们的观察，我们不能自信地提出1 E 1547.0-5408的近红外对应物。对物体1进行更多的NIR观测，例如确定其颜色和监测可变性，将是决定性的，以确定它是否可以被认为是合理的候选者。
英文摘要：
Despite about a decade of observations, very little is known about the optical and infrared (IR) emission properties of the Soft Gamma-ray Repeaters (SGRs) and of the Anomalous X-ray Pulsars (AXPs), the magnetar candidates, and about the physical processes which drive their emission at these wavelengths. This is mainly due to the limited number of identifications achieved so far, five in total, and to the sparse spectral coverage obtained from multi-band optical/IR photometry. Aim of this work is to search for a likely candidate counterpart to the recently discovered transient radio AXP 1E 1547.0-5408. We performed the first deep near-IR (NIR) observations (Ks band) of 1E 1547.0-5408 with the VLT on three nights (July 8th, 12th, and August 17th), after the X-ray source rebrightening and during the subsequent decay reported around June 2007. We detected four objects within, or close to, the 3sigma radio position of 1E 1547.0-5408. The faintest of them (object 1) has a brightness K = 20.27 +/- 0.05, which would yield an unabsorbed X-ray to NIR flux ratio FX/FKs ~ 800 for 1E 1547.0-5408, i.e. on average lower than those derived for other magnetars. The non-detection of object 1 on the nights of July 8th and August 17th only allowed us to set an upper limit of Delta Ks ~ 0.2 on its NIR variability, which prevented us to search for correlations with the radio or X-ray flux. We detected no other object at the radio position down to a limit of Ks ~ 21.7 (at 5sigma), computed in our deepest VLT image (July 12th). From our observations we can not confidently propose a NIR counterpart to 1E 1547.0-5408. More NIR observations of object 1, e.g. to determine its colors and to monitor variability, would be conclusive to determine whether or not it can be considered a plausible candidate.
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