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Register a new userScattered Short Gamma-Ray Bursts as Electromagnetic Counterparts to Gravitational Waves and Implications of GW170817 and GRB 170817A
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In the faint short gamma-ray burst sGRB 170817A followed by the gravitational waves (GWs) from a merger of two neutron stars (NSs) GW170817, the spectral peak energy is too high to explain only by canonical off-axis emission. We investigate off-axis appearance of an sGRB prompt emission scattered by a cocoon, which is produced through the jet-merger-ejecta interaction, with either sub-relativistic or mildly-relativistic velocities. We show that the observed properties of sGRB 170817A, in particular the high peak energy, can be consistently explained by the Thomson-scattered emission with a typical sGRB jet, together by its canonical off-axis emission, supporting that an NS-NS merger is the origin of sGRBs. The scattering occurs at $lesssim 10^{10}$--$10^{12},{rm cm}$ not far from the central engine, implying the photospheric or internal shock origin of the sGRB prompt emission. The boundary between the jet and cocoon is sharp, which could be probed by future observations of off-axis afterglows. The scattering model predicts a distribution of the spectral peak energy that is similar to the observed one but with a cutoff around $sim$ MeV energy, and its correlations with the luminosity, duration, and time lag from GWs, providing a way to distinguish it from alternative models.
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We investigate prolonged engine activities of short gamma-ray bursts (SGRBs), such as extended and/or plateau emissions, as high-energy gamma-ray counterparts to gravitational waves (GWs). Binary neutron-star mergers lead to relativistic jets and merger ejecta with $r$-process nucleosynthesis, which are observed as SGRBs and kilonovae/macronovae, respectively. Long-term relativistic jets may be launched by the merger remnant as hinted in X-ray light curves of some SGRBs. The prolonged jets may dissipate their kinetic energy within the radius of the cocoon formed by the jet-ejecta interaction. Then the cocoon supplies seed photons to non-thermal electrons accelerated at the dissipation region, causing high-energy gamma-ray production through the inverse Compton scattering process. We numerically calculate high-energy gamma-ray spectra in such a system using a one-zone and steady-state approximation, and show that GeV--TeV gamma-rays are produced with a duration of $10^2-10^5$ seconds. They can be detected by {it Fermi}/LAT or CTA as gamma-ray counterparts to GWs.
We investigate the possible origin of extended emissions (EEs) of short gamma-ray bursts with an isotropic energy of ~ 10^(50-51) erg and a duration of a few 10 s to ~ 100 s, based on a compact binary (neutron star (NS)-NS or NS-black hole (BH)) merger scenario. We analyze the evolution of magnetized neutrino-dominated accretion disks of mass ~ 0.1 M_sun around BHs formed after the mergers, and estimate the power of relativistic outflows via the Blandford-Znajek (BZ) process. We show that a rotation energy of the BH up to > 10^52 erg can be extracted with an observed time scale of > 30 (1+z) s with a relatively small disk viscosity parameter of alpha < 0.01. Such a BZ power dissipates by clashing with non-relativistic pre-ejected matter of mass M ~ 10^-(2-4) M_sun, and forms a mildly relativistic fireball. We show that the dissipative photospheric emissions from such fireballs are likely in the soft X-ray band (1-10 keV) for M ~ 10^-2 M_sun possibly in NS-NS mergers, and in the BAT band (15-150 keV) for M ~ 10^-4 M_sun possibly in NS-BH mergers. In the former case, such soft EEs can provide a good chance of ~ 6 yr^-1 for simultaneous detections of the gravitational waves with a ~ 0.1 deg angular resolution by soft X-ray survey facilities like Wide-Field MAXI.
We present the results of the search for gravitational waves (GWs) associated with $gamma$-ray bursts detected during the first observing run of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO). We find no evidence of a GW signal for any of the 41 $gamma$-ray bursts for which LIGO data are available with sufficient duration. For all $gamma$-ray bursts, we place lower bounds on the distance to the source using the optimistic assumption that GWs with an energy of $10^{-2}M_odot c^2$ were emitted within the $16$-$500,$Hz band, and we find a median 90% confidence limit of 71$,$Mpc at 150$,$Hz. For the subset of 19 short/hard $gamma$-ray bursts, we place lower bounds on distance with a median 90% confidence limit of 90$,$Mpc for binary neutron star (BNS) coalescences, and 150 and 139$,$Mpc for neutron star-black hole coalescences with spins aligned to the orbital angular momentum and in a generic configuration, respectively. These are the highest distance limits ever achieved by GW searches. We also discuss in detail the results of the search for GWs associated with GRB 150906B, an event that was localized by the InterPlanetary Network near the local galaxy NGC 3313, which is at a luminosity distance of 54$,$Mpc ($z=0.0124$). Assuming the $gamma$-ray emission is beamed with a jet half-opening angle $leq 30^{circ}$, we exclude a BNS and a neutron star-black hole in NGC 3313 as the progenitor of this event with confidence $>99$%. Further, we exclude such progenitors up to a distance of 102$,$Mpc and 170$,$Mpc, respectively.
Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.
In this paper, we study the luminosity function and formation rate of short gamma-ray bursts (sGRBs). Firstly, we derive the $E_p-L_p$ correlation using 16 sGRBs with redshift measurements and determine the pseudo redshifts of 284 Fermi sGRBs. Then, we use the Lynden-Bell c$^-$ method to study the luminosity function and formation rate of sGRBs without any assumptions. A strong evolution of luminosity $L(z)propto (1+z)^{4.47}$ is found. After removing this evolution, the luminosity function is $ Psi (L) propto L_0 ^ {- 0.29 pm 0.01} $ for dim sGRBs and $ psi (L) propto L_0 ^ {- 1.07 pm 0.01} $ for bright sGRBs, with the break point $8.26 times 10^{50} $ erg s$^{-1}$. We also find that the formation rate decreases rapidly at $z<1.0$, which is different with previous works. The local formation rate of sGRBs is 7.53 events Gpc$^{-3}$ yr$^{-1}$. Considering the beaming effect, the local formation rate of sGRBs including off-axis sGRBs is $ 203.31^{+1152.09}_{-135.54} $ events Gpc$^{-3}$ yr$^{-1}$. We also estimate that the event rate of sGRBs detected by the advanced LIGO and Virgo is $0.85^{+4.82}_{-0.56} $ events yr$^{-1}$ for NS-NS binary.
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