标题： 2008年Mrk421的伽马射线爆发通过ARGO-YBJ探测器观测 显示英文标题

标题： Gamma ray flares from Mrk421 in 2008 observed with the ARGO-YBJ detector

摘要： 2008年，耀星Markarian 421进入了一个非常活跃的阶段，并成为TeV能量下天空中最明亮的天体之一，表现出频繁的爆发事件。 使用位于羊八井（海拔4300米，西藏，中国）的全覆盖宇宙射线簇射探测器ARGO-YBJ的数据，我们在整个年度内监测了伽马射线能量E > 0.3 TeV的源。 观测到的流量是变化的，最强的爆发发生在三月和六月，与X射线增强活动相关。 虽然在特定事件中TeV流量可以比蟹状星云的流量大几倍，但第41天到第180天的平均辐射几乎达到蟹状星云水平的两倍，对于能量E > 1 TeV的积分流量为(3.6 +-0.6) 10^-11光子 cm^-2 s^-1，并在之后有所下降。 本文集中研究了六月上半月发生的爆发。 由于月光干扰了切连科夫望远镜在最强烈辐射期间的观测，这一时期从光学到100 MeV伽马射线已被深入研究，并部分扩展到TeV能量。 我们的数据补充了这些观测，在6月11日至13日检测到了一个统计显著性为3.8个标准差的信号，对应于高于1 TeV的伽马射线流量约为蟹状星云的6倍。 校正了星系间吸收后的重建微分谱可以用一个指数为alpha = -2.1的幂律来表示，延伸到几个TeV。 谱斜率与之前观察到的流量和谱指数之间的相关性完全一致，表明这一特性在不同时期保持不变，并且描述了源的辐射过程。 显示英文摘要

摘要： In 2008 the blazar Markarian 421 entered a very active phase and was one of the brightest sources in the sky at TeV energies, showing frequent flaring episodes. Using the data of ARGO-YBJ, a full coverage air shower detector located at Yangbajing (4300 m a.s.l., Tibet, China), we monitored the source at gamma ray energies E > 0.3 TeV during the whole year. The observed flux was variable, with the strongest flares in March and June, in correlation with X-ray enhanced activity. While during specific episodes the TeV flux could be several times larger than the Crab Nebula one, the average emission from day 41 to 180 was almost twice the Crab level, with an integral flux of (3.6 +-0.6) 10^-11 photons cm^-2 s^-1 for energies E > 1 TeV, and decreased afterwards. This paper concentrates on the flares occurred in the first half of June. This period has been deeply studied from optical to 100 MeV gamma rays, and partially up to TeV energies, since the moonlight hampered the Cherenkov telescope observations during the most intense part of the emission. Our data complete these observations, with the detection of a signal with a statistical significance of 3.8 standard deviations on June 11-13, corresponding to a gamma ray flux about 6 times larger than the Crab one above 1 TeV. The reconstructed differential spectrum, corrected for the intergalactic absorption, can be represented by a power law with an index alpha = -2.1 extending up to several TeV. The spectrum slope is fully consistent with previous observations reporting a correlation between the flux and the spectral index, suggesting that this property is maintained in different epochs and characterizes the source emission processes.