利用OVRO-LWA 31小时全天资料对低频射电瞬变天空的新限制
New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO-LWA
摘要：
我们提出的第一个瞬态调查的结果，欧文斯谷射电天文台长波长阵列（OVRO-LWA）使用31小时的数据，在其中，我们把最约束的限制瞬时瞬态表面密度在13秒的时间尺度为几分钟，频率低于100 MHz。OVRO-LWA是一种偶极阵列，可在13 s节奏下以58 MHz的带宽（27 MHz至84 MHz）对整个可视半球进行成像。在6.5 $σ$通量密度限值10.5 Jy以上未检测到瞬变，这意味着在探测的最短时间尺度下，瞬变表面密度的上限为$2.5\times10^{-8}$ deg $^{-2}$，这比在低于100 MHz频率和迄今为止可比通量密度下实现的要深几个数量级。OVRO-LWA调查中未检测到瞬变，特别是在几分钟长的时间尺度上，使我们能够对Stewart等人发现的潜在瞬变群体的速率进行进一步限制。从它们的瞬态速率，我们期望检测到$8.4^{+31.8}_{-8.0}$事件，并且我们的零检测的概率是$1.9^{+644}_{-1.9}\times10^{-3}$，在平坦谱和宽带宽的假设下，在18.1 Jy的通量密度极限处以95%的置信度排除瞬态速率$>1.4\times10^{-4} \text{days}^{-1} \text{deg}^{-2}$。我们讨论了我们的nondetection这个人口和进一步的限制，可以对源的光谱指数，固有的发射带宽，以及由此产生的光度分布的影响。
英文摘要：
We present the results of the first transient survey from the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) using 31 hr of data, in which we place the most constraining limits on the instantaneous transient surface density at timescales of 13 s to a few minutes and at frequencies below 100 MHz. The OVRO-LWA is a dipole array that images the entire viewable hemisphere with 58 MHz of bandwidth from 27 to 84 MHz at 13 s cadence. No transients are detected above a 6.5$σ$ flux density limit of 10.5 Jy, implying an upper limit to the transient surface density of $2.5\times10^{-8}$ deg$^{-2}$ at the shortest timescales probed, which is orders of magnitude deeper than has been achieved at sub-100 MHz frequencies and comparable flux densities to date. The nondetection of transients in the OVRO-LWA survey, particularly at minutes-long timescales, allows us to place further constraints on the rate of the potential population of transients uncovered by Stewart et al. (2016). From their transient rate, we expect a detection of $8.4^{+31.8}_{-8.0}$ events, and the probability of our null detection is $1.9^{+644}_{-1.9}\times10^{-3}$, ruling out a transient rate $>1.4\times10^{-4} \text{days}^{-1} \text{deg}^{-2}$ with 95% confidence at a flux density limit of 18.1 Jy, under the assumption of a flat spectrum and wide bandwidth. We discuss the implications of our nondetection for this population and further constraints that can be made on the source spectral index, intrinsic emission bandwidth, and resulting luminosity distribution.
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