RUI: Using the Earth as a Gravitational Wave Detector

物理学家面临的重要挑战之一， 天文学家在接下来的十年里， 引力波（GW）。 大部分的实验努力， 过去的二十年一直致力于发展探测器， 它们对毫秒级的辐射很敏感 伴随着恒星的引力坍缩 对象 一个有用的基准，用于比较 随机背景是宇宙的闭合密度。 如果存在能量密度远大于 比这更大的将与目前的限制冲突， 减速参数 脉冲星计时的局限性 和微波背景各向同性都是几个数量级 幅值低于每倍频程的闭合密度。 a的限制 来自地面的毫赫兹随机背景 地震观测值要高得多，几次闭合 密度每倍频程;然而，使用地球作为GW探测器 具有提供对固有的 探测器的波动。 这几乎是不可能的， 以上两种方法。 在之前的NSF资助下，Boughn教授分析了超过 IDA全球项目收集的100个台站年数据 地震仪网络，以寻找异常 地球低频四极模激发 引力辐射的随机背景。 的 不存在OS 2和4S 2模式的平均激发 允许他设定上限的背景， 0.31 mHz和1.72 mHz的引力波， 每八度的宇宙临界密度 数量级低于以前的限制。 根据本 奖，他将寻找oS 2模式的脉冲激励， 分析最安静的IDA站的数据， 低地震背景噪音。 灵敏度限值， 由背景地震噪声施加的，对应于 h的无量纲应变幅10-13。 为了 评估地球作为一个 引力波探测器，他将计算预期的 地面源激发OS 2模式。

One of the important challenges facing physicists and astronomers in the next decade is the direct detection of gravitation waves (GW's). Most of the experimental effort in the last twenty years has been directed at developing detectors which are sensitive to the millisecond bursts of radiation expected to accompany the gravitational collapse of stellar objects. A useful benchmark with which to compare limits on a stochastic background is the closure density of the universe. The existence of a background with an energy density much larger than this would conflict with current limits on the deceleration parameter. The limits implied by pulsar timing and microwave background isotropy are both several orders of magnitude below closure density per octave. Limits on a millihertz stochastic background derived from terrestrial seismic observations are much higher, several times closure density per octave; however, using the earth as a GW detector has the advantage of providing discrimination against intrinsic fluctuations in the detector. This is virtually impossible for the above two methods. Under a previous NSF grant Prof. Boughn analyzed more than 100 station-years of data collected by the Project IDA global network of seismometers in order to look for anomalous excitation of the low frequency quadrupole modes of the earth by a stochastic background of gravitational radiation. The absence of an average excitation of the oS2 and 4S2 modes allowed him to set upper limits on a background of gravitational waves at 0.31 mHz and 1.72 mHz of a few times the critical density of the universe per octave which is several orders of magnitude lower than previous limits. Under this award, he would search for pulse excitation of the oS2 modes by analyzing the data of the quietest IDA stations during periods of low seismic background noise. The sensitivity limit which is imposed by background seismic noise corresponds to a dimensionless strain amplitude of h 10-13. In order to evaluate the ultimate usefulness of the earth as a gravitational wave detector he will compute the expected excitation of the oS2 mode by terrestrial sources.