耀斑星和周期源TVLM 513-46546的Gamma-ray辐射的叠加搜索
A Stacking Search for Gamma-ray Emission from Nearby Flare Stars and the Periodic Source TVLM 513-46546
摘要：
到目前为止，太阳是唯一一颗在伽马射线中被发现的孤立的主序星，特别是在强烈的耀斑期间。年轻的超冷矮星要活跃得多，因此它们也是可能的伽马射线源。我们使用费米伽马射线太空望远镜近12年的数据，对97颗最近的X射线和射电耀斑星进行了空间叠加，以寻找GeV辐射。叠加残差图显示无显著信号。模拟上限表明，峰值恒星通量至少比噪声水平低7倍。我们还分析了快速旋转射电星TVLM 513-46546的相位折叠光变曲线，报告了一个试探性的（TS = 30）脉冲信号，并对其周期进行了修正。我们通过分析附近的费米目录源和测试场，并通过使用不同的周期重复分析，来检查假阳性信号的可能性。尽管清楚地检测到目录源，但是没有发现其他周期信号，并且TVLM 513的TS值系统地增加到最佳周期。假设的伽马射线信号几乎与光学峰值同相，与无线电脉冲的相位相差0.4 +/- 0.05转。这些结果表明，从相对论质子流下通量管朝向光球活动区的排放。质子与大气层碰撞产生中性π介子，衰变为伽马射线光子。这将是第一次在伽马射线中探测到一颗正常的孤立恒星，也是迄今为止恒星磁层中质子加速的最有力证据。
英文摘要：
So far, the Sun is the only isolated main sequence star detected in gamma-rays, particularly during powerful flares. Young ultracool dwarfs are far more active so they are also plausible gamma-ray sources. We performed a spatial stack of 97 of the nearest X-ray and radio flare stars to search for GeV emission using nearly 12 years of data from the Fermi Gamma-ray Space Telescope. The stacked residual maps showed no significant signal. Modeling the upper limits indicates a peak stellar flux at least a factor of 7 below the noise level. We also analyzed the phase-folded light curve of the rapidly rotating radio star TVLM 513-46546, report a tentative (TS = 30) pulsed signal, and refine its period. We examine the possibility of a false positive signal by analyzing nearby Fermi catalog sources and test fields, and by repeating the analysis using different periods. No other periodic signals are found, despite clear detections of the catalog sources, and the TS value for TVLM 513 increases systematically to the optimal period. The putative gamma-ray signal is nearly in phase with the optical peak, and out of phase with the radio pulses by 0.4 +/- 0.05 rotations. These results argue for emission from relativistic protons streaming down flux tubes towards the photospheric active regions. The protons colliding with the atmosphere create neutral pions that decay into gamma-ray photons. This would be the first detection of a normal, isolated star in gamma-rays, and the strongest evidence yet for proton acceleration in stellar magnetospheres.
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