New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO–LWA
New Limits on the Low-frequency Radio Transient Sky Using 31 hr of All-sky Data with the OVRO–LWA
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DOI：
10.3847/1538-4357/ab4f87
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发表时间：
2019-11
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通讯作者：
M. Anderson;G. Hallinan;M. Eastwood;R. Monroe;T. Callister;J. Dowell;B. Hicks;Yuping Huang;N. Kassim;J. Kocz;T. Joseph W. Lazio;Danny C. Price;F. Schinzel;Greg. B. Taylor
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作者：
M. Anderson;G. Hallinan;M. Eastwood;R. Monroe;T. Callister;J. Dowell;B. Hicks;Yuping Huang;N. Kassim;J. Kocz;T. Joseph W. Lazio;Danny C. Price;F. Schinzel;Greg. B. Taylor
我们展示了欧文斯谷射电天文台长波长阵列 (OVRO-LWA) 使用 31 小时数据进行的第一次瞬变测量的结果，其中我们对 13 秒到几分钟的时间尺度和低于 100 MHz 的频率下的瞬时瞬变表面密度设置了最严格的限制。 OVRO-LWA 是一个偶极子阵列，可在 27 至 84 MHz 之间以 58 MHz 带宽以 13 秒的节奏对整个可视半球进行成像。在 10.5 Jy 的 6.5σ 磁通密度极限之上没有检测到瞬态，这意味着在探测的最短时间尺度上瞬态表面密度的上限为 2.5 × 10−8 deg−2，这比迄今为止在低于 100 MHz 频率和可比磁通密度下实现的要深几个数量级。 OVRO-LWA 调查中没有检测到瞬变，特别是在几分钟的时间尺度上，这使我们能够对 Stewart 等人发现的潜在瞬变总体的比率施加进一步的限制。根据它们的瞬态速率，我们期望检测到事件，并且零检测的概率为 ，排除瞬态速率 >1.4 × 10−4 days−1 deg−2 ，在平坦频谱和宽带宽的假设下，通量密度限制为 18.1 Jy，置信度为 95%。我们讨论了未检测到这一群体的影响，以及可以对源光谱指数、固有发射带宽和所得光度分布进行的进一步限制。
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 6.5σ flux density limit of 10.5 Jy, implying an upper limit to the transient surface density of 2.5 × 10−8 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. From their transient rate, we expect a detection of events, and the probability of our null detection is , ruling out a transient rate >1.4 × 10−4 days−1 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.