Double neutron star (DNS) merger events are promosing candidates of shortGamma-ray Burst (sGRB) progenitors as well as high-frequecy gravitational wave(GW) emitters. On August 17, 2017, such a coinciding event was detected by boththe LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-RayMonitor on board NASA's {\it Fermi} Space Telescope as GRB 170817A. Here weshow that the fluence and spectral peak energy of this sGRB fall into the lowerportion of the distributions of known sGRBs. Its peak isotropic luminosity isabnormally low. The estimated event rate density above this luminosity is atleast $190^{+440}_{-160} {\rm Gpc^{-3} \ yr^{-1}}$, which is close to but stillbelow the DNS merger event rate density. This event likely originates from astructured jet viewed from a large viewing angle. There are similar faint softGRBs in the {\it Fermi} archival data, a small fraction of which might belongto this new population of nearby, low-luminosity sGRBs.
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机译：双中子星（DNS）合并事件是短伽玛射线爆裂（sGRB）祖细胞以及高频引力波（GW）发射器的候选人。 2017年8月17日，LIGO-Virgo引力波检测器网络GW170817和NASA {\ it Fermi}太空望远镜上的Gamma-RayMonitor都将GRB 170817A检测到了这种重合事件。在这里，我们显示此sGRB的能量密度和频谱峰值能量落入已知sGRB分布的较低部分。其峰值各向同性亮度异常低。高于此亮度的估计事件速率密度至少为$ 190 ^ {+ 440} _ {-160} {\ rm Gpc ^ {-3} \ yr ^ {-1}} $，虽然接近但仍低于DNS合并事件速率密度。此事件可能是由于从大视角观察到的结构化射流引起的。 {\ it Fermi}档案数据中也有类似的模糊softGRB，其中一小部分可能属于附近低光度sGRB的这一新群体。
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