Title: Flare genesis in relativistic jet: Disentangling the drivers of variability in the blazar 4C +27.50 Show Chinese title

Title: 相对论喷流中的耀斑起源：解开耀变体 4C +27.50变化驱动因素的纠缠

Abstract: Recently, blazar 4C +27.50 was found to be flaring in gamma-rays since its detection with Fermi-LAT in 2008. For the first time, a dedicated temporal and spectral study of the blazar 4C +27.50 has been performed in this work to understand the nature of this object. We used the Bayesian block algorithm to identify four flaring states and one quiet state in the 2-year-long Fermi-LAT light curve. Simultaneous broadband flaring episodes have been observed, and a significant correlation is seen between optical and $\gamma$-ray emission, suggesting the co-spatial origin of the broadband emission. The variation of fractional variability amplitude with respect to frequency shows a nearly double hump structure similar to broadband SED. The fastest flux doubling time in the 1-day binned $\gamma$-ray light curve is found to be about 7.8 hours. A curvature in $\gamma$-ray spectra has been observed, possibly caused by a stochastic particle acceleration process rather than radiative cooling. No evident correlation was found in the $\gamma$-ray flux-index plot, but a clear harder-when-brighter trend is observed in the X-ray flux-index plot. A one-zone leptonic model has been implemented to understand broadband emission during the quiet and flaring states, and the variation of the jet parameters is been investigated. A gradual increment in BLR and Disk energy density has been observed from a quiet to the flaring state. Broadband SED modeling suggested that an enhancement in the magnetic field, particle energy, and bulk Lorentz factor might have caused the flaring events. Show Chinese abstract

Abstract: 近期，耀变体 4C +27.50 被发现自2008年被费米伽马射线空间望远镜（Fermi-LAT）探测到以来一直处于伽马射线爆发状态。 首次，本研究针对4C +27.50 进行了专门的时间和光谱研究，以理解该天体的性质。 我们使用贝叶斯块算法在两年长的Fermi-LAT光变曲线中识别出四个爆发态和一个安静态。 同时观测到了多波段爆发事件，并且光学与$\gamma$光子发射之间显示出显著的相关性，表明宽带发射具有共空间起源。 关于频率的分数变化幅度的变化显示出了类似于宽带SED的近似双峰结构。 在1天分箱的$\gamma$光子光变曲线中，最快的流量加倍时间约为7.8小时。 观察到了$\gamma$光子谱的曲率，可能由随机粒子加速过程而非辐射冷却引起。 在$\gamma$光子流量指数图中没有发现明显相关性，但在X射线流量指数图中观察到了明显的“越亮越硬”的趋势。 采用单区电子模型来理解安静态和爆发态下的宽带发射，并研究喷流参数的变化。 从安静态到爆发态，观测到了BLR和盘能量密度的逐渐增加。 宽带SED建模表明磁场、粒子能量和整体洛伦兹因子的增强可能是导致爆发事件的原因。