罗马5期耀变体多波段目录BZUs的分类

利用支持向量机(Support Vector Machine,SVM)、随机森林(Random Forest,RF)、集成学习(Ensemble Learning,EM)和多层感知机(Multi-Layer Perceptron,MLP)将罗马5期耀变体多波段目录(The 5th edition of the Roma-BZCAT Multifrequency Catalogue of Blazars,5BZCAT)中227个不确定类型的耀变体(Blazars of Uncertain type,BZUs)分为蝎虎天体候选体和平谱射电类星体候选体,并通过特征工程和网格搜索方法提高分类准确率。综合4种分类器的分类结果,将判别概率阈值设为0.8,得到33个蝎虎天体候选体和119个平谱射电类星体候选体。

3C66A的光学观测与周期分析

用国家天文台兴隆观测站1.26 m红外/光学望远镜,在2019年9月~2020年1月间对BL Lac天体3C66A进行了SDSS-g,r,i 3个波段的光学观测。利用功率谱方法、Jurkevich方法及离散相关函数分别对其光变曲线进行了周期性分析。结果显示,3C66A存在约32.0 d的光变周期,其可用螺旋喷流模型进行解释。

Optimization of performance of the KM2A full array using the Crab Nebula

The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energyγ-rays using data collected from August 2021 to August 2022,resulting in an improvement in significance of the detection in the Crab Nebula of approximately 15%,compared with that of previous cuts.With the implementation of these new selection criteria,the angular resolution was also significantly improved by approximately 10%at tens of TeV.Other aspects of the full KM2A array performance,such as the pointing error,were also calibrated using the Crab Nebula.The resulting energy spectrum of the Crab Nebula in the energy range of 10-1000 TeV are well fitted by a log-parabola model,which is consistent with the previous results from LHAASO and other experiments.

Flux variations of cosmic ray air showers detected by LHAASO-KM2A during a thunderstorm on June 10,2021

The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,2021.The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields,with a maximum fractional increase of 20%.The variations in trigger rates(increases or decreases)were found to be strongly dependent on the primary zenith angle.The flux of secondary particles increased significantly,following a trend similar to that of shower events.To better understand the observed behavior,Monte Carlo simulations were performed with CORSIKA and G4KM2A(a code based on GEANT4).We found that the experimental data(in saturated negative fields)were in good agreement with the simulations,assuming the presence of a uniform electric field of-700 V/cm with a thickness of 1500 m in the atmosphere above the observation level.Due to the acceleration/deceleration by the atmospheric electric field,the number of secondary particles with energy above the detector threshold was modified,resulting in the changes in shower detection rate.

Performance of LHAASO-WCDA and observation of the Crab Nebula as a standard candle

The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.