Searches for signals from cosmic point-like sources of high energy neutrinos in 5 years of AMANDA-II data
Searches for signals from cosmic point-like sources of high energy neutrinos in 5 years of AMANDA-II data
复制标题
在 5 年的 AMANDA-II 数据中搜索来自宇宙点状高能中微子源的信号
作者：
M. Ackermann
阿曼达-II是一台位于南极冰川冰中的中微子望远镜。通过中微子的Erenkov光发射，优化了对能量大于100GeV的中微子诱发的Muon轨迹的探测。我们分析了2000年至2004年1001天探测器运行期间收集的数据，以寻找来自点状中微子源的信号。这样的信号预计来自宇宙物体，它们会将强子加速到非常高的能量，然后与周围的质子或光子相互作用。在阿曼达-II中记录的主要事件类别是在大气中宇宙射线的相互作用中产生的µ子。由于能量损失，介子无法穿透地球，并具有下行方向。因此，识别中微子诱导事件的主要标志是它的上升方向。4282个上行事件的样本是从为本分析选择的时段内触发的100亿个事件中提取的。通过寻找大气中微子各向同性背景上的局域过剩，在该数据样本上完成了对点源的搜索。该程序适用于候选源的方向，如活动星系核、超新星遗迹和X射线双星。在第二步中，扫描整个北方的天空，寻找未知的来源。此外，我们还研究了提高对被怀疑为高度可变的中微子发射源的探测机会的方法。我们寻找中微子事件在源的高活动期的过剩，这取决于它在某些频带内的电磁发射强度。一个基于滑动时间窗的额外测试被应用于中微子区域的数据集，这在时间综合搜索中是不可见的。在分析的数据集中，既没有发现局域过剩，也没有发现中微子。因此，我们计算了与这一观测结果相容的中微子u的上限。一个组合νμ+ντUX的能谱为dΦ/de∝E−2的平均上限为E 2 dΦ/de=1.0·10−7GeV cm−2 S−1。这是迄今报道的对点源中微子u的最严格的上限。
AMANDA-II is a neutrino telescope located in the glacial ice at the South Pole. It is optimized to detect neutrino induced muon tracks with energies larger than 100 GeV by their erenkov light emission. We analyzed the data collected in 1001 e ective days of detector operation between the years 2000 and 2004 for a signal from point-like sources of neutrinos. Such a signal is expected from cosmic objects that accelerate hadrons to very high energies, which subsequently interact with ambient protons or photons. The dominant event class recorded in AMANDA-II are muons produced in the interactions of cosmic rays in the atmosphere. Due to their energy loss, the muons cannot penetrate the Earth and have down-going directions. The main signature to identify a neutrino induced event is therefore its up-going direction. A sample of 4282 up-going events is extracted from the 10 billion events triggered in the period selected for this analysis. The search for point sources is accomplished on this data sample by looking for a localized excess over the isotropic background of atmospheric neutrinos. The procedure is applied for the directions of candidate sources, like Active Galactic Nuclei, Supernova remnants and X-ray binaries. In a second step, the full northern sky is scanned for unknown sources. Further, we investigate methods to enhance the detection chance for sources which are suspected to be highly variable neutrino emitters. We search for an excess of neutrino events in periods of high activity of a source, de ned by the intensity of its electromagnetic emission in certain frequency bands. An additional test based on a sliding time window is applied to the dataset to nd ares of neutrinos, which would not be visible in the time-integrated search. Neither a localized excess nor a neutrino are has been found in the analyzed dataset. Therefore, we calculate upper limits on the neutrino uxes which are compatible with this observation. The average upper limit achieved for a combined νμ+ντ ux with a spectrum of dΦ/dE ∝ E−2 is E2 dΦ/dE = 1.0 · 10−7 GeV cm−2 s−1 assuming a avor ratio of 1 : 1. It represents the most stringent upper limit on neutrino uxes from point-like sources reported so far.