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We consider a magnetar flare model for fast radio bursts (FRBs). We show that millisecond bursts of sufficient power can be generated by synchrotron maser emission ignited at the reverse shock propagating through the weakly magnetized material that forms the magnetar flare. If the maser emission is generated in an anisotropic regime (due to the geometry of the production region or presence of an intense external source of stimulating photons), the duration of the maser flashes is similar to the magnetar flare duration even if the shock front radius is large. Our scenario allows for relaxing the requirements for several key parameters: the magnetic field strength at the production site, luminosity of the flare, and the production site bulk Lorentz factor. To check the feasibility of this model, we study the statistical relation between powerful magnetar flares and the rate of FRBs. The expected ratio is derived by convoluting the redshift-dependent magnetar density with its flare luminosity function above the energy limit determined by the FRB detection threshold. We obtain that only a small fraction, ∼10âˆ'5, of powerful magnetar flares trigger FRBs. This ratio agrees surprisingly well with our estimates: we obtained that 10% of magnetars should be in the evolutionary phase suitable for the production of FRBs, and only 10âˆ'4 of all flares are expected to be weakly magnetized, which is a necessary condition for the high-frequency maser emission. [ABSTRACT FROM AUTHOR]

We present a brief history and the current status of research on gamma-ray bursts (GRBs), including observations at various GRB phases: the prompt emission, afterglow, supernova/kilonova, and the host galaxy. An overview of the known phenomenological features and theoretical models for GRBs is given. Problems, the solution of which is necessary for a successful study of the phenomenon of GRB, are discussed. [ABSTRACT FROM AUTHOR]

We have developed a model of early X-ray afterglows of gamma-ray bursts originating from the reverse shock (RS) propagating through ultrarelativistic, highly magnetized pulsar-like winds produced by long-lasting central engines. We first performed fluid and magnetohydrodynamic numerical simulations of relativistic double explosions. We demonstrate that even for constant properties of the wind a variety of temporal behaviors can be produced, depending on the energy of the initial explosion and the wind power, the delay time for the switch-on of the wind, and the magnetization of the wind. X-ray emission of the highly magnetized RS occurs in the fast-cooling regime—this ensures high radiative efficiency and allows fast intensity variations. We demonstrate that (i) RS emission naturally produces light curves, showing power-law temporal evolution with various temporal indices; (ii) mild wind power, of the order of ∼1046 erg s−1 (equivalent isotropic), can reproduce the afterglows' plateau phase; (iii) termination of the wind can produce sudden steep decays; and (iv) short-duration afterglow flares are due to mild variations in the wind luminosity, with small total injected energy. [ABSTRACT FROM AUTHOR]

HESS J0632+057 is an eccentric gamma-ray Be binary that produces non-thermal radio, Xrays, GeV and very high-energy gamma-rays. The non-thermal emission of HESS J0632+057 is modulated with the orbital period, with a dominant maximum before apastron passage. The nature of the compact object in HESS J0632+057 is not known, although it has been proposed to be a young pulsar as in PSR B1259–63, the only gamma-ray emitting high-mass binary known to host a non-accreting pulsar. In this letter, we present hydrodynamical simulations of HESS J0632+057 in the context of a pulsar and a stellar wind interacting in an eccentric binary, and propose a scenario for the non-thermal phenomenology of the source. In this scenario, the non-thermal activity before and around apastron is linked to the accumulation of non-thermal particles in the vicinity of the binary, and the sudden drop of the emission before apastron is produced by the disruption of the two-wind interaction structure, allowing these particles to escape efficiently. In addition to providing a framework to explain the nonthermal phenomenology of the source, this scenario predicts extended, moving X-ray emitting structures similar to those observed in PSR B1259-63. [ABSTRACT FROM AUTHOR]

ABSTRACT The existence of extended emission (EE) is an intriguing property of short-duration gamma-ray bursts, because the nature of the EE is still unclear. It might be a rising X-ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short-duration gamma-ray bursts, emphasizing the common properties of both short bursts and short bursts with EE. Assuming that the EE with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra EE by different off axis position of observer. The model involves a short-duration jet, which is powered by heating due to annihilation, and a long-lived Blandford-Znajek jet with a significantly narrow opening angle. Our proposed model is a plausible mechanism for short-duration burst energization. It can explain short bursts both with and without EE within a single class of progenitor. [ABSTRACT FROM AUTHOR]

We present numerical simulations of axisymmetric, magnetically driven outflows that reproduce the inferred properties of ultrarelativistic gamma-ray burst (GRB) jets. These results extend our previous simulations of outflows accelerated to moderately relativistic speeds, which are applicable to jets of active galactic nuclei. In contrast to several recent investigations, which have employed the magnetodynamics approximation, our numerical scheme solves the full set of equations of special relativistic, ideal magnetohydrodynamics, which enables us to explicitly calculate the jet velocity and magnetic-to-kinetic energy conversion efficiency – key parameters of interest for astrophysical applications. We confirm that the magnetic acceleration scheme remains robust into the ultrarelativistic regime, as previously indicated by semi-analytic self-similar solutions. We find that all current-carrying outflows exhibit self-collimation and consequent acceleration near the rotation axis, but that unconfined outflows lose causal connectivity across the jet and therefore do not collimate or accelerate efficiently in their outer regions. We show that magnetically accelerated jets confined by an external pressure that varies as assume a paraboloidal shape (where are cylindrical coordinates and ), and we obtain analytic expressions for the one-to-one correspondence between the pressure distribution and the asymptotic jet shape. We demonstrate that the acceleration efficiency of jets with paraboloidal streamlines is ≳50 per cent, with the numerical value being higher the lower the initial magnetization. We derive asymptotic analytic expressions for the acceleration of initially cold outflows along paraboloidal streamlines and verify that they provide good descriptions of the simulated flows. Our modelled jets (corresponding to ) attain Lorentz factors on scales , consistent with the possibility that long/soft GRB jets are accelerated within envelopes of collapsing massive stars, and on scales , consistent with the possibility that short/hard GRB jets are accelerated on scales where they can be confined by moderately relativistic winds from accretion discs. We also find that for outflows that undergo an efficient magnetic-to-kinetic energy conversion, where is the opening half-angle of the poloidal streamlines. This relation implies that the γ-ray emitting components of GRB outflows accelerated in this way are very narrow, with in regions where , and that the afterglow light curves of these components would either exhibit a very early jet break or show no jet break at all. [ABSTRACT FROM AUTHOR]

Bolometric light curves for the afterglow resulting from the passage of a gamma-ray burst through a molecular cloud are computed. The profile and duration of the afterglow light curve depend strongly on the distribution of matter in the cloud, the degree of collimation of the gamma-ray radiation, and the observing conditions. The peak can be reached as soon as seven days (the gamma-ray burst is located at some distance from the center of a molecular cloud with small-scale density enhancements), or as long as one to three years (the gamma-ray burst is located at the center of a uniform molecular cloud) after the burst. The bolometric luminosity of the re-radiated signal can reach 6.5×1042 erg/s.© 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]