In the era of time-domain, multi-messenger astronomy, the detection of transient events on the high-energy electromagnetic sky has become more important than ever. Previous attempts to systematically search for onboard-untriggered events in the data of Fermi-GBM have been limited to short-duration signals with variability time scales smaller than ~1 min due to the dominance of background variations on longer timescales. In this study, we aim at the detection of slowly rising or long-duration transient events with high sensitivity and full coverage of the GBM spectrum. We make use of our earlier developed physical background model, propose a novel trigger algorithm with a fully automatic data analysis pipeline. The results from extensive simulations demonstrate that the developed trigger algorithm is sensitive down to sub-Crab intensities, and has a near-optimal detection performance. During a two month test run on real Fermi-GBM data, the pipeline detected more than 300 untriggered transient signals. For one of these transient detections we verify that it originated from a known astrophysical source, namely the Vela X-1 pulsar, showing pulsed emission for more than seven hours. More generally, this method enables a systematic search for weak and/or long-duration transients.
翻译:在时间范围、多信使天文学的时代,探测高能电磁天空上的瞬间事件比以往更加重要。以前在Fermi-GBM数据中系统搜索机载突发事件的努力仅限于短时间信号,其变异时间范围小于~1分钟,因为背景变异在较长时间尺度上占主导地位。在这项研究中,我们的目标是探测缓慢上升或长期变化的瞬间事件,其GBM频谱具有高度敏感度和全面覆盖度。我们利用我们早期开发的物理背景模型,提出带有完全自动数据分析管道的新型触发算法。广泛模拟的结果显示,开发的触发算法对亚克拉强度敏感,并且具有接近最佳的检测性。在对真正的Fermi-GBM数据进行两个月测试期间,管道探测到300多个未变异的瞬间信号。对于其中之一,我们核实它来自已知的天体源,即Vela X-1和较弱的脉冲反射时,能够普遍显示脉冲式脉冲辐射的系统搜索方法。