We use the observed properties of fast radio bursts (FRBs) and a number of general physical considerations to provide a broad-brush model for the physical properties of FRB sources and the radiation mechanism. We show that the magnetic field in the source region should be at least 10 14 Gauss. This strong field is required to ensure that the electrons have sufficiently high ground state Landau energy so that particle collisions, instabilities, and strong electromagnetic fields associated with the FRB radiation do not perturb electrons' motion in the direction transverse to the magnetic field and destroy their coherent motion; coherence is required by the high observed brightness temperature of FRB radiation. The electric field in the source region required to sustain particle motion for a wave period is estimated to be of order 10 11 esu. These requirements suggest that FRBs are produced near the surface of magnetars perhaps via forced reconnection of magnetic fields to produce episodic, repeated, outbursts. The beaming-corrected energy release in these bursts is estimated to be about 10 36 ergs, whereas the total energy in the magnetic field is at least ∼ 10 45 ergs. We provide a number of predictions for this model which can be tested by future observations. One of which is that short duration FRB-like bursts should exist at much higher frequencies, possibly up to optical.

No abstract

Abstract-This paper describes the incorporation of an accurate physics-based model of the resonant tunneling diode (RTD) into Berkeley SPICE version 3F5 and addresses the related direct current (dc) and transient convergence problems caused by the negative differential resistance (NDR) and the exponential nature of the device characteristics. To circumvent the dc convergence problems, a new continuation technique using artificial parameter embedding and a current limiting algorithm are proposed. The studies made in this paper have shown that these techniques are superior to the in-built continuation methods of SPICE, such as Gmin-stepping and Source-stepping, for a large number of circuits of varying sizes. To improve transient convergence performance, the following three algorithms are added to SPICE: a modified forced-convergence algorithm, a new time-step adjustment algorithm, and a modified device voltage prediction algorithm.

Black hole-neutron star (BHNS) binaries are amongst promising candidates for the joint detection of electromagnetic (EM) signals with gravitational waves (GWs) and are expected to be detected in the near future. Here we study the effect of the BHNS binary parameters on the merger ejecta properties and associated EM signals. We estimate the remnant disk and unbound ejecta masses for BH mass and spin distributions motivated from the observations of transient low-mass X-ray binaries (LMXBs) and specific NS equation of state (EoS). The amount of r-process elements synthesised in BHNS mergers is estimated to be a factor of ∼ 10 2 − 10 4 smaller than BNS mergers, due to the smaller dynamical ejecta and merger rates for the former. We compute the EM luminosities and light curves for the early-and late-time emissions from the ultrarelativistic jet, sub-relativistic dynamical ejecta and wind, and the mildly-relativistic cocoon for typical ejecta parameters. We then evaluate the low-latency EM follow-up rates of the GW triggers in terms of the GW detection rateṄ GW for current telescope sensitivities and typical BHNS binary parameters to find that most of the EM counterparts are detectable for high BH spin, small BH mass and stiffer NS EoS when NS disruption is significant. Based on the relative detection rates for given binary parameters, we find the ease of EM follow-up to be: ejecta afterglow > cocoon afterglow jet prompt > ejecta macronova > cocoon prompt > jet afterglow >> wind macronova >> wind afterglow.

We study the spectra of photospheric emission from highly relativistic gamma-ray burst outflows using a Monte Carlo (MC) code. We consider the Comptonization of photons with a fast cooled synchrotron spectrum in a relativistic jet with realistic photon to electron number ratio N γ /N e = 10 5 , using mono-energetic protons which interact with thermalised electrons through Coulomb interaction. The photons, electrons and protons are cooled adiabatically as the jet expands outwards. We find that the initial energy distribution of the protons and electrons do not have any appreciable effect on the photon peak energy E γ,peak and the power-law spectrum above E γ,peak . The Coulomb interaction between the electrons and the protons does not affect the output photon spectrum significantly as the energy of the electrons is elevated only marginally. E γ,peak and the spectral indices for the low and high energy power-law tails of the photon spectrum remain practically unchanged even with electron-proton coupling. Increasing the initial optical depth τ in results in slightly shallower photon spectrum below E γ,peak and fewer photons at the high-energy tail, although f ν ∝ ν −0.5 above E γ,peak and up to ∼ 1 MeV, independent of τ in . We find that E γ,peak determines the peak energy and the shape of the output photon spectrum. Lastly, we find that our simulation results are quite sensitive to N γ /N e , for N e = 3 × 10 3 . For almost all our simulations, we obtain an output photon spectrum with power-law tail above E γ,peak extending up to ∼ 1 MeV.