400 research outputs found
The effects of Time-Variable Absorption due to Gamma-Ray Bursts In Active Galactic Nuclei Accretion Disks
Both long and short gamma-ray bursts (GRBs) are expected to occur in the
dense environments of active galactic nuclei (AGN) accretion disks. As these
bursts propagate through the disks they live in, they photoionize the medium
causing time-dependent opacity that results in transients with unique spectral
evolution. In this paper we use a line-of-sight radiation transfer code
coupling metal and dust evolution to simulate the time-dependent absorption
that occurs in the case of both long and short GRBs. Through these simulations,
we investigate the parameter space in which dense environments leave a
potentially observable imprint on the bursts. Our numerical investigation
reveals that time dependent spectral evolution is expected for central
supermassive black hole masses between and solar masses
in the case of long GRBs, and between and solar masses in the
case of short GRBs. Our findings can lead to the identification of bursts
exploding in AGN disk environments through their unique spectral evolution
coupled with a central location. In addition, the study of the time-dependent
evolution would allow for studying the disk structure, once the identification
with an AGN has been established. Finally, our findings lead to insight into
whether GRBs contribute to the AGN emission, and which kind, thus helping to
answer the question of whether GRBs can be the cause of some of the as-of-yet
unexplained AGN time variability
Intrinsic properties of the engine and jet that powered the short gamma-ray burst associated with GW170817
GRB 170817A was a subluminous short gamma-ray burst detected about 1.74 s
after the gravitational wave signal GW170817 from a binary neutron star (BNS)
merger. It is now understood as an off-axis event powered by the cocoon of a
relativistic jet pointing 15 to 30 degrees away from the direction of
observation. The cocoon was energized by the interaction of the incipient jet
with the non-relativistic baryon wind from the merger remnant, resulting in a
structured outflow with a narrow core and broad wings. In this paper, we couple
the observational constraints on the structured outflow with a model for the
jet-wind interaction to constrain the intrinsic properties with which the jet
was launched by the central engine, including its time delay from the merger
event. Using wind prescriptions inspired by magnetized BNS merger simulations,
we find that the jet was launched within about 0.4 s from the merger, implying
that the 1.74 s observed delay was dominated by the fireball propagation up to
the photospheric radius. We also constrain, for the first time for any
gamma-ray burst, the jet opening angle at injection and set a lower limit to
its asymptotic Lorentz factor. These findings suggest an initially
Poynting-flux dominated jet, launched via electromagnetic processes. If the jet
was powered by an accreting black hole, they also provide a significant
constraint on the survival time of the metastable neutron star remnant.Comment: Accepted for publication in Ap
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