Abstract
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. On August 17, 2017, such a coinciding event was detected by both the LIGO-Virgo gravitational wave detector network as GW170817 and Gamma-Ray Monitor on board NASA’s Fermi Space Telescope as GRB 170817A. Here, we show that the fluence and spectral peak energy of this sGRB fall into the lower portion of the distributions of known sGRBs. Its peak isotropic luminosity is abnormally low. The estimated event rate density above this luminosity is at least 190_{ - 160}^{ + 440} Gpc−3 yr−1, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. There are similar faint soft GRBs in the Fermi archival data, a small fraction of which might belong to this new population of nearby, low-luminosity sGRBs.
Highlights
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst progenitors as well as high-frequency gravitational wave (GW) emitters
Short-duration gamma-ray bursts have long been proposed to be produced in systems involving the coalescence of double neutron stars (DNS)[1], and the observations of short gamma-ray burst (sGRB) afterglows and host galaxies are consistent with such a conjecture[2,3,4]
By extracting the photon events from the Time-Tagged Event (TTE) data detected by these two detectors, we noticed that a sharp peak is present in the light curve between T0 − 0.26 s and T0 + 0.57 s with a signal-to-noise ratio (S/N) >5 (Methods)
Summary
Double neutron star (DNS) merger events are promising candidates of short gamma-ray burst (sGRB) progenitors as well as high-frequency gravitational wave (GW) emitters. The estimated event rate density above this luminosity is at least 190þÀ414600 Gpc−3 yr−1, which is close to but still below the DNS merger event rate density. This event likely originates from a structured jet viewed from a large viewing angle. Short-duration gamma-ray bursts (sGRBs) have long been proposed to be produced in systems involving the coalescence of double neutron stars (DNS)[1], and the observations of sGRB afterglows and host galaxies are consistent with such a conjecture[2,3,4]. We discussed the possible jet geometries, the physical implication of the time delay between GW signal and GRB signal, and the possible merger products of the event
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