scholarly journals Jet propagation in expanding medium for gamma-ray bursts

2020 ◽  
Vol 500 (1) ◽  
pp. 627-642
Author(s):  
Hamid Hamidani ◽  
Kunihito Ioka
Keyword(s):  
Numerical Simulations ◽  
Gamma Ray ◽  
Ambient Medium ◽  
Gamma Ray Bursts ◽  
Analytical Models ◽  
Opening Angle ◽  
Binary Neutron Star ◽  
Merger Event ◽  
Lateral Width ◽  
Jet Collimation

ABSTRACT The binary neutron star (BNS) merger event GW170817 clearly shows that a BNS merger launches a short gamma-ray burst (sGRB) jet. Unlike collapsars, where the ambient medium is static, in BNS mergers the jet propagates through the merger ejecta that is expanding outward at substantial velocities (∼0.2c). Here, we present semi-analytical and analytical models to solve the propagation of GRB jets through their surrounding media. These models improve our previous model by including the jet collimation by the cocoon self-consistently. We also perform a series of 2D numerical simulations of jet propagation in BNS mergers and in collapsars to test our models. Our models are consistent with numerical simulations in every aspect (the jet head radius, the cocoon’s lateral width, the jet opening angle including collimation, the cocoon pressure, and the jet–cocoon morphology). The energy composition of the cocoon is found to be different depending on whether the ambient medium is expanding or not; in the case of BNS merger jets, the cocoon energy is dominated by kinetic energy, while it is dominated by internal energy in collapsars. Our model will be useful for estimating electromagnetic counterparts to gravitational waves.

scholarly journals Gamma-Ray Bursts and Binary Neutron Star Mergers

1996 ◽  
Vol 165 ◽  
pp. 489-502
Author(s):  
Tsvi Piran
Keyword(s):  
Neutron Star ◽  
Gravitational Radiation ◽  
Gamma Ray ◽  
Indirect Evidence ◽  
Gamma Ray Bursts ◽  
Binary Neutron Star ◽  
Merger Event ◽  
Γ Rays ◽  
Γ Ray ◽  
The One

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1913+16, end their life in a catastrophic merger event (denoted here NS2M). The merger releases ∼5 1053 ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2Ms providing only indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational-radiation signal could confirm this model.

scholarly journals Collimated outflows from long-lived binary neutron star merger remnants

2020 ◽  
Vol 495 (1) ◽  
pp. L66-L70 ◽  
Author(s):  
Riccardo Ciolfi
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Spin Axis ◽  
Binary Neutron Star ◽  
Physical Conditions ◽  
Massive Neutron Star ◽  
Merger Event ◽  
First Time

ABSTRACT The connection between short gamma-ray bursts (SGRBs) and binary neutron star (BNS) mergers was recently confirmed by the association of GRB 170817A with the merger event GW170817. However, no conclusive indications were obtained on whether the merger remnant that powered the SGRB jet was an accreting black hole (BH) or a long-lived massive neutron star (NS). Here, we explore the latter case via BNS merger simulations covering up to 250 ms after merger. We report, for the first time in a full merger simulation, the formation of a magnetically driven collimated outflow along the spin axis of the NS remnant. For the system at hand, the properties of such an outflow are found largely incompatible with an SGRB jet. With due consideration of the limitations and caveats of our present investigation, our results favour a BH origin for GRB 170817A and SGRBs in general. Even though this conclusion needs to be confirmed by exploring a larger variety of physical conditions, we briefly discuss possible consequences of all SGRB jets being powered by accreting BHs.

scholarly journals Optical Afterglows as Probes for the Central Engine and Fireball of Gamma-Ray Bursts

2012 ◽  
Vol 8 (S290) ◽  
pp. 263-264
Author(s):  
Liang Li ◽  
En-Wei Liang ◽  
He Gao ◽  
Bing Zhang
Keyword(s):  
Statistical Analysis ◽  
Gamma Rays ◽  
Density Profile ◽  
Gamma Ray ◽  
Ambient Medium ◽  
Gamma Ray Bursts ◽  
Prompt Gamma ◽  
Medium Density ◽  
Central Engine ◽  
Prompt Emission

AbstractWell-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are compiled from literature. We identify possible emission components based on our empirical fits and present statistical analysis for these components. We find that the flares are related to prompt emission, suggesting that they could have the same origin in different episodes. The shallow decay segment is not correlated with prompt gamma-rays. It likely signals a long-lasting injected wind from GRB central engines. Early after onset peak is closely related with prompt emission. The ambient medium density profile is likely n ∝ r−1. No correlation between the late re-brightening bump and prompt gamma-rays or the onset bump is found. They may be from another jet component.

scholarly journals Constraints on the circumburst environments of short gamma-ray bursts

2020 ◽  
Vol 495 (4) ◽  
pp. 4782-4799 ◽  
Author(s):  
Brendan O’Connor ◽  
Paz Beniamini ◽  
Chryssa Kouveliotou
Keyword(s):  
Gamma Ray ◽  
Galactic Halo ◽  
Gamma Ray Bursts ◽  
Light Curves ◽  
Host Galaxy ◽  
Host Galaxies ◽  
Binary Neutron Star ◽  
Range Of Values ◽  
Short Grbs

ABSTRACT Observational follow up of well localized short gamma-ray bursts (SGRBs) has left $20\!-\!30{{\ \rm per\ cent}}$ of the population without a coincident host galaxy association to deep optical and NIR limits (≳26 mag). These SGRBs have been classified as observationally hostless due to their lack of strong host associations. It has been argued that these hostless SGRBs could be an indication of the large distances traversed by the binary neutron star system (due to natal kicks) between its formation and its merger (leading to an SGRB). The distances of GRBs from their host galaxies can be indirectly probed by the surrounding circumburst densities. We show that a lower limit on those densities can be obtained from early afterglow light curves. We find that ${\lesssim}16{{\ \rm per\ cent}}$ of short GRBs in our sample took place at densities ≲10−4 cm−3. These densities represent the expected range of values at distances greater than the host galaxy’s virial radii. We find that out of the five SGRBs in our sample that have been found to be observationally hostless, none are consistent with having occurred beyond the virial radius of their birth galaxies. This implies one of two scenarios. Either these observationally hostless SGRBs occurred outside of the half-light radius of their host galaxy, but well within the galactic halo, or in host galaxies at moderate to high redshifts (z ≳ 2) that were missed by follow-up observations.

scholarly journals On the opening angle of magnetized jets from neutron-star mergers: the case of GRB170817A

2020 ◽  
Vol 495 (4) ◽  
pp. 3780-3787 ◽  
Author(s):  
Antonios Nathanail ◽  
Ramandeep Gill ◽  
Oliver Porth ◽  
Christian M Fromm ◽  
Luciano Rezzolla
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Initial Conditions ◽  
Observation Angle ◽  
Opening Angle ◽  
Binary Neutron Star ◽  
Best Fitting ◽  
Standard Picture ◽  
General Relativistic ◽  
Star Binary

ABSTRACT The observations of GW170817/GRB170817A have confirmed that the coalescence of a neutron-star binary is the progenitor of a short gamma-ray burst (GRB). In the standard picture of a short GRB, a collimated highly relativistic outflow is launched after merger and it successfully breaks out from the surrounding ejected matter. Using initial conditions inspired from numerical-relativity binary neutron-star merger simulations, we have performed general-relativistic hydrodynamic (HD) and magnetohydrodynamic (MHD) simulations in which the jet is launched and propagates self-consistently. The complete set of simulations suggests that: (i) MHD jets have an intrinsic energy and velocity polar structure with a ‘hollow core’ subtending an angle θcore ≈ 4°–5° and an opening angle of θjet > ≳ 10°; (ii) MHD jets eject significant amounts of matter and two orders of magnitude more than HD jets; (iii) the energy stratification in MHD jets naturally yields the power-law energy scaling E(> Γβ) ∝ (Γβ)−4.5; (iv) MHD jets provide fits to the afterglow data from GRB170817A that are comparatively better than those of the HD jets and without free parameters; and (v) finally, both of the best-fitting HD/MHD models suggest an observation angle θobs ≃ 21° for GRB170817A.

scholarly journals Accelerating AGN jets to parsec scales using general relativistic MHD simulations

2019 ◽  
Vol 490 (2) ◽  
pp. 2200-2218 ◽  
Author(s):  
K Chatterjee ◽  
M Liska ◽  
A Tchekhovskoy ◽  
S B Markoff
Keyword(s):  
Ambient Medium ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Opening Angle ◽  
Long Baseline ◽  
General Relativistic ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations ◽  
Jet Collimation ◽  
Sheath Structure

ABSTRACT Accreting black holes produce collimated outflows, or jets, that traverse many orders of magnitude in distance, accelerate to relativistic velocities, and collimate into tight opening angles. Of these, perhaps the least understood is jet collimation due to the interaction with the ambient medium. In order to investigate this interaction, we carried out axisymmetric general relativistic magnetohydrodynamic simulations of jets produced by a large accretion disc, spanning over 5 orders of magnitude in time and distance, at an unprecedented resolution. Supported by such a disc, the jet attains a parabolic shape, similar to the M87 galaxy jet, and the product of the Lorentz factor and the jet half-opening angle, γθ ≪ 1, similar to values found from very long baseline interferometry (VLBI) observations of active galactic nuclei (AGNs) jets; this suggests extended discs in AGNs. We find that the interaction between the jet and the ambient medium leads to the development of pinch instabilities, which produce significant radial and lateral variability across the jet by converting magnetic and kinetic energy into heat. Thus pinched regions in the jet can be detectable as radiating hotspots and may provide an ideal site for particle acceleration. Pinching also causes gas from the ambient medium to become squeezed between magnetic field lines in the jet, leading to enhanced mass loading and deceleration of the jet to non-relativistic speeds, potentially contributing to the spine-sheath structure observed in AGN outflows.

scholarly journals Jet Propagation in Neutron Star Mergers and GW170817

2019 ◽  
Author(s):  
Hamid Hamidani ◽  
Kenta Kiuchi ◽  
Kunihito Ioka
Keyword(s):  
Neutron Star ◽  
Numerical Simulations ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Expansion Velocity ◽  
Analytic Model ◽  
Binary Neutron Star ◽  
Central Engine ◽  
Relativistic Jet ◽  
Wave Event

Abstract The gravitational wave event from the binary neutron star (BNS) merger GW170817 and the following multi-messenger observations present strong evidence for i) merger ejecta expanding with substantial velocities and ii) a relativistic jet which had to propagate through the merger ejecta. The ejecta’s expansion velocity is not negligible for the jet head motion, which is a fundamental difference from the other systems like collapsars and active galactic nuclei. Here we present an analytic model of the jet propagation in an expanding medium. In particular, we notice a new term in the expression of the breakout time and velocity. In parallel, we perform a series of over a hundred 2D numerical simulations of jet propagation. The BNS merger ejecta is prepared based on numerical relativity simulations of a BNS merger with the highest-resolution to date. We show that our analytic results agree with numerical simulations over a wide parameter space. Then we apply our analytic model to GW170817, and obtain two solid constraints on: i) the central engine luminosity as Liso, 0 ∼ 3 × 1049 − 2.5 × 1052 erg s−1, and on ii) the delay time between the merger and engine activation t0 − tm < 1.3 s. The engine power implies that the apparently-faint short gamma-ray burst (sGRB) sGRB 170817A is similar to typical sGRBs if observed on-axis.

scholarly journals Towards Improving the Prospects for Coordinated Gravitational-Wave and Electromagnetic Observations

2011 ◽  
Vol 7 (S285) ◽  
pp. 358-360 ◽  
Author(s):  
Ilya Mandel ◽  
Luke Z. Kelley ◽  
Enrico Ramirez-Ruiz
Keyword(s):  
Gravitational Wave ◽  
Prior Information ◽  
Gamma Ray ◽  
Optimal Parameter ◽  
Gamma Ray Bursts ◽  
Binary Neutron Star ◽  
Quantitative Estimates ◽  
Optimal Parameter Estimation ◽  
Parameter Estimation Techniques

AbstractWe discuss two approaches to searches for gravitational-wave (GW) and electromagnetic (EM) counterparts of binary neutron-star mergers. The first approach relies on triggering archival searches of GW detector data based on detections of EM transients. Quantitative estimates of the improvement to GW detector reach due to the increased confidence in the presence and parameters of a signal from a binary merger gained from the EM transient suggest utilizing other transients in addition to short gamma-ray bursts. The second approach involves following up GW candidates with targeted EM observations. We argue for the use of slower but optimal parameter-estimation techniques and for a more sophisticated use of astrophysical prior information, including galaxy catalogues to find preferred follow-up locations.

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