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arXiv 1303.6282astro-ph.COastro-ph.HE
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在扩展的Chandra深场南部对射电变量和瞬变的灵敏搜索

Sensitive Search For Radio Variables And Transients In The Extended Chandra Deep-Field South

K. P. Mooley, D. A. Frail, E. O. Ofek, N. A. Miller, S. R. Kulkarni, A. Horesh

摘要:

我们报告的分析扩展钱德拉深场南(E-CDFS)区域使用档案数据从甚大阵列,研究无线电变异性和瞬变的目标在次mJy级。E-CDFS在1.4 GHz采样时间尺度上的49个历元观测从1天到3个月不等。我们发现,只有一小部分(1%)的未解决的无线电源以上40微焦耳是可变的4西格玛水平。没有证据表明分数变率随着低于1毫扬斯基的射电源群的已知转变而变化。对这些辐射源的光学鉴别表明,这些射电辐射与活动星系核或恒星形成星系的中心区域有关。在详细比较了各种源查找算法的效能后,我们采用最佳的算法进行了瞬态搜索。没有发现瞬变现象,这意味着峰值通量密度大于0.21 mJy的瞬变现象的面密度小于0.37 deg^-2(置信水平为95%)。该结果比Bower等人(2007)在5 GHz下测量的瞬态速率低约一个数量级,但与Frail等人(2012)最近的上限一致。我们的研究结果表明,1.4 GHz的无线电天空相对安静。对于多波长瞬态搜索,例如引力波的电磁对应物,该频率对于减少假阳性的高背景可能是最佳的。

英文摘要:

We report on an analysis of the Extended Chandra Deep Field South (E-CDFS) region using archival data from the Very Large Array, with the goal of studying radio variability and transients at the sub-mJy level. The 49 epochs of E-CDFS observations at 1.4 GHz sample timescales from one day to 3 months. We find that only a fraction (1%) of unresolved radio sources above 40 uJy are variable at the 4-sigma level. There is no evidence that the fractional variability changes along with the known transition of radio source populations below one milliJansky. Optical identifications of the sources show that the variable radio emission is associated with the central regions of an active galactic nucleus or a star-forming galaxy. After a detailed comparison of the efficacy of various source-finding algorithms, we use the best to carry out a transient search. No transients were found. This implies that the areal density of transients with peak flux density greater than 0.21 mJy is less than 0.37 deg^-2 (at a confidence level of 95%). This result is approximately an order of magnitude below the transient rate measured at 5 GHz by Bower et al. (2007) but it is consistent with more recent upper limits from Frail et al. (2012). Our findings suggest that the radio sky at 1.4 GHz is relatively quiet. For multi-wavelength transient searches, such as the electromagnetic counterparts to gravitational waves, this frequency may be optimal for reducing the high background of false positives.

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