毫秒脉冲相干去色散门控成像
Coherently dedispersed gated imaging of millisecond pulsars
摘要：
出于快速定位新发现的微弱毫秒星（MSP）的需要，我们开发了一种相干去色散门控相关器。该选通相关器考虑了二进制中MSP的轨道运动，同时在同时生成的波束形成器输出中使用从周期性搜索导出的最佳拟合拓扑中心旋转模型来折叠vibrium。独特的应用程序的门相关器的敏感的干涉研究的MSP说明使用巨型米波射电望远镜（GMRT）干涉阵列。我们可以明确地定位五个新发现的费米MSP在开关门控图像平面的精度为+-1”。对这种精确位置的即时了解允许使用阵列望远镜的敏感相干光束进行后续定时观测，这大大减少了望远镜时间的使用（对于GMRT来说约为20倍）。此外，精确的先验天体测量位置减少了时间拟合中的大协方差的影响（与发现位置，脉冲星周期导数和未知的二元模型），这反过来又加速了收敛到初始定时模型。例如，当用精确的先验位置（± 1”）拟合时，计时模型在大约100天内收敛，考虑了位置和脉冲星周期导数之间的协方差的影响。此外，这种精确的位置允许在其他波段的脉冲星对应物的快速识别。我们还报告了一种新的方法，在波束相位校准使用的开关门控图像的目标脉冲星，它提供了最佳的灵敏度的相干阵列去除可能的时间和空间消相干。
英文摘要：
Motivated by the need for rapid localisation of newly discovered faint millisecond pulsars (MSPs) we have developed a coherently dedispersed gating correlator. This gating correlator accounts for the orbital motions of MSPs in binaries while folding the visibilities with best-fit topocentric rotational model derived from periodicity search in simultaneously generated beamformer output. Unique applications of the gating correlator for sensitive interferometric studies of MSPs are illustrated using the Giant Metrewave Radio Telescope (GMRT) interferometric array. We could unambiguously localise five newly discovered Fermi MSPs in the on-off gated image plane with an accuracy of +-1". Immediate knowledge of such precise position allows the use of sensitive coherent beams of array telescopes for follow-up timing observations, which substantially reduces the use of telescope time (~ 20X for the GMRT). In addition, precise a-priori astrometric position reduces the effect of large covariances in timing fit (with discovery position, pulsar period derivative and unknown binary model), which in-turn accelerates the convergence to initial timing model. For example, while fitting with precise a-priori position (+-1"), timing model converges in about 100 days, accounting the effect of covariance between position and pulsar period derivative. Moreover, such accurate positions allows for rapid identification of pulsar counterpart at other wave-bands. We also report a new methodology of in-beam phase calibration using the on-off gated image of the target pulsar, which provides the optimal sensitivity of the coherent array removing the possible temporal and spacial decoherences.
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