Operation of the Milagro Gamma Ray Observatory

米拉格罗伽马射线天文台的运行

• 批准号: 0400424
• 负责人: Jordan Goodman
• 金额: --
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-01 至 2008-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0400424&HistoricalAwards=false
• 关键词: Operation; Milagro; Gamma; Ray; Observatory

Very high energy gamma ray astronomy probes some of the most extreme environments in the known universe. Known sources of TeV gamma rays contain compact objects (black holes or neutron stars) with intense gravitational and/or magnetic fields. Known sources of TeV gamma rays include supernova remnants within our galaxy and active galactic nuclei outside of our galaxy. Other possible sources include gamma-ray bursts, micro-quasars, diffuse emission from cosmic rays interacting with matter in our own galaxy, and more exotic objects such as primordial black holes and weakly interacting massive particles. Six sources of TeV photons have been detected in the northern hemisphere. The paucity of known sources is due to both the available instrumentation and the sources. The combination of transient sources and narrow field instruments makes the detection of new sources difficult. Milagro is the first detector capable of continuously monitoring the entire overhead sky at energies above a few hundred GeV. Milagro is a water Cherenkov extensive air shower detector located near Los Alamos, NM at 2630m above sea level, consisting of a ~5,000 m2 central (pond) detector surrounded by an array of 175 instrumented water tanks, (outriggers) that span an area of roughly 40,000 m2. The Milagro pond is a 6-million gallon water reservoir, which measures 80m x 60m x 8m deep and is covered with a light-tight cover. The reservoir is instrumented with 723 20-cm PMTs on a 2.8m x 2.8m grid. The PMTs are deployed in two layers. The top layer of 450 PMTs is under 1.5 meters of water and the bottom layer of 273 PMTs is under 6 meters of water. Timing of the arrival of the shower particles is used to determine the direction of the primary air shower. During the three years we have been operating we have developed a robust method for reducing the cosmic ray background and used this rejection method to detect TeV gamma rays from the Crab Nebula, Mrk 421, and to see the first evidence for diffuse TeV emission from the galactic plane. In addition, we have monitored the northern hemisphere for both transient and steady sources of TeV photons. To date we have observed emission only from the three sources mentioned above. We have now set the best limits on TeV sources in the northern hemisphere over all timescales from 1 millisecond to 2.5 years. During the past year we have implemented a real-time analysis system that allows us to detect a gamma-ray burst within 4 seconds of its occurrence and to send an alert to other observatories. We have not yet detected significant emission from any region within our field of view on timescales from 1ms to 2hrs. During this period there were relatively few bursts detected by the HETE and INTEGRAL satellites. Later this year the launch of SWIFT will provide us with a rich dataset to search for coincident TeV emission from gamma-ray bursts. Just as Milagrito, our prototype, observed significant emission from one GRB detected by BASTE we expect the advent of SWIFT to prove a fruitful period for Milagro. This proposal will allow us to continue to operate Milagro for the next three years. During the past two years several improvements have been made to the detector. We have implemented an intelligent triggering system that has enabled us to substantially lower the trigger threshold of Milagro. This has increased the effective area at 100 GeV four-fold - critical for detecting gamma-ray bursts. Most importantly, we have just completed the construction of an array of 175 water tanks that surround the pond. These tanks improve the energy and angular resolution and the background rejection capabilities of Milagro. We have obtained a 3-fold increase in sensitivity now that these detectors are incorporated into our event reconstruction. Milagro data are easy to explain to students and the general public, who often have difficulty understanding how we claim to see particles that they don't. The collaboration has been very active in exposing students and the general public to the excitement of the particle astrophysics (PA) field. Each year we bring undergraduate students to work on Milagro and generally involve students in analysis. In addition, we give on average eight talks each year at high schools and at least two public lectures on the subject of PA. He also works with the US Physics Olympics team. In addition, he works with the Maryland program for 8th and 10th grade girls. He also started the physics "Question of the Week" (see it at www.physics.umd.edu) that is used by many teachers world-wide.

极高能伽马射线天文学探测已知宇宙中一些最极端的环境。 已知的TeV伽马射线源包含具有强烈引力和/或磁场的致密物体（黑洞或中子星）。 TeV伽马射线的已知来源包括我们星系内的超新星遗迹和我们星系外的活动星系核。 其他可能的来源包括伽马射线爆发，微类星体，宇宙射线与我们银河系中的物质相互作用产生的漫射辐射，以及更奇特的物体，如原始黑洞和弱相互作用的大质量粒子。 在北方半球已经探测到六个TeV光子源。 已知来源的缺乏是由于现有的仪器和来源。 瞬态源和窄场仪器的组合使得新源的检测变得困难。 Milagro是第一个能够以超过几百GeV的能量连续监测整个头顶天空的探测器。Milagro是一个水切伦科夫广泛的空气簇射探测器，位于新墨西哥州洛斯阿拉莫斯附近，海拔2630米，由一个约5，000平方米的中央（池塘）探测器组成，周围有175个仪表水箱（外伸支架），面积约为40，000平方米。Milagro池塘是一个600万加仑的蓄水池，其尺寸为80米x 60米x 8米深，并覆盖着不透光的盖子。在2.8 m x 2.8 m网格上，用723个20 cm光电倍增管对储层进行测量。PMT部署在两层中。450个PMT的顶层在1.5米的水下，273个PMT的底层在6米的水下。簇射粒子到达的时间用于确定一次风簇射的方向。在我们已经运作的三年中，我们已经开发出一种强大的方法来减少宇宙射线的背景，并使用这种拒绝方法来检测TeV的伽马射线从蟹状星云，Mrk 421，并看到第一个证据弥漫TeV的发射从银道面。 此外，我们监测了北方半球的瞬态和稳定的TeV光子源。 到目前为止，我们只观察到上述三个来源的排放。 我们现在已经为北方半球从1毫秒到2.5年的所有时间尺度上的TeV源设定了最佳限制。 在过去一年中，我们实施了一个实时分析系统，使我们能够在伽马射线爆发发生后4秒内检测到它，并向其他观测站发送警报。我们还没有从我们视野内的任何区域检测到从1毫秒到2小时的时间尺度上的显著发射。 在此期间，HETE和INTEGRAL卫星探测到的爆发相对较少。 今年晚些时候，SWIFT的推出将为我们提供丰富的数据集，以搜索伽马射线爆发的同步TeV发射。 正如我们的原型Milagrito从BASTE探测到的一个GRB中观察到显著的发射一样，我们预计SWIFT的出现将证明Milagro是一个富有成效的时期。该提案将使我们能够在未来三年内继续运营Milagro。在过去的两年里，对探测器进行了几次改进。 我们已经实施了一个智能触发系统，使我们能够大大降低Milagro的触发阈值。 这增加了探测伽马射线爆发的100 GeV四倍临界有效区域。 最重要的是，我们刚刚完成了围绕池塘的175个水箱阵列的建设。 这些坦克提高了能量和角度分辨率以及Milagro的背景抑制能力。 我们已经获得了3倍的灵敏度增加，现在这些探测器被纳入我们的事件重建。Milagro的数据很容易向学生和公众解释，他们通常很难理解我们如何声称看到了他们没有看到的粒子。该合作一直非常积极地让学生和公众接触粒子天体物理学（PA）领域的兴奋。每年我们都会让本科生参与Milagro的工作，并通常让学生参与分析。此外，我们平均每年在高中举行八次讲座，并至少举行两次关于PA主题的公开讲座。 他还与美国物理奥林匹克队合作。此外，他还与马里兰州的8年级和10年级女生项目合作。他还开始了物理“每周问题”（见www.physics.umd.edu），这是由世界各地的许多教师使用。