2,768 research outputs found
Accretion Power in GRBs
I discuss the implication of the temporal structure of GRBs to the nature of their inner engine. I argue that the temporal strucutre shows that GRBs must involve internal shocks (or another kind of internal interaction within a relativistic outflow). To produce these internal shocks GRB
inner engines must vary on a time scale of a fraction of a second and, on the other hand, they should be active for the whole duration of the burst, namely for several dozen of seconds. This implies that from the point of view of the central engine GRBs are a "quasi steady state" phenomenon. Accretion onto a newly formed black hole is the most likely mechanism that can satisfy these conditions and can power GRBs. I discuss the implication of accretion models of massive disks around black holes to GRB modelling
Gamma-Ray Bursts - a Primer For Relativists
Gamma-Ray Bursts (GRBs) - short bursts of 100-1MeV photons arriving from
random directions in the sky are probably the most relativistic objects
discovered so far. Still, somehow they did not attract the attention of the
relativistic community. In this short review I discuss briefly GRB observations
and show that they lead us to the fireball model - GRBs involve macroscopic
relativistic motion with Lorentz factors of a few hundred or more. I show that
GRB sources involve, most likely, new born black holes, and their progenitors
are Supernovae or neutron star mergers. I show that both GRB progenitors and
the process of GRB itself produce gravitational radiation and I consider the
possibility of detecting this emission. Finally I show that GRBs could serve as
cosmological indicators that could teach us about the high redshift () dark ages of the universe.Comment: Review talk given at GR1
Gamma-Ray Bursts from Neutron Star Mergers
Binary neutron stars merger (NSM) at cosmological distances is probably
the only -ray bursts model based on an independently observed
phenomenon which is known to be taking place at a comparable rate. We describe
this model, its predictions and some open questions.Comment: 4 pages, 1 Figure can be obtained on request by e-mail from the
Autho
Gamma-Ray Bursts and Neutron Star Mergers - Possibly the Strongest Explosions in the Universe
-ray bursts have baffled theorists ever since their accidental
discovery at the sixties. We suggest that these bursts originate in merger of
neutron star binaries, taking place at cosmological distances. These mergers
release , in what are possibly the strongest explosions in
the Universe. If even a small fraction of this energy is channeled to an
electromagnetic signal it will be detected as a grbs. We examine the virtues
and limitations of this model and compare it with the recent Compton \g-ray
observatory results.Comment: 8 pages, to appear in the XXVI INTERNATIONAL HIGH ENERGY PHYSICS
CONFERENC
Gamma-Ray Bursts and Binary Neutron Star Mergers
Neutron star binaries, such as the one observed in the famous binary pulsar
PSR 1916+13, end their life in a catastrophic merge event (denoted here
NSM). The merger releases ergs, mostly as
neutrinos and gravitational radiation. A small fraction of this energy suffices
to power -ray bursts (GRBs) at cosmological distances. Cosmological
GRBs must pass, however, an optically thick fireball phase and the observed
-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 NSMs being only an indirect evidence for this
model). In the future a coinciding detection of a GRB and a gravitational
radiation signal could confirm this model.Comment: 13 pages, uuencoded ps files to apprear in IAU SYMPOSIUM 165 `COMPACT
STARS IN BINARIES' 15-19 August 1994, The Hague, Netherland
Gamma-Ray Bursts - When Theory Meets Observations
Gamma-Ray Bursts (GRBs) are the brightest objects observed. They are also the
most relativistic objects known so far. GRBs occur when an ultrarelativisitic
ejecta is slowed down by internal shocks within the flow. Relativistic
particles accelerated within these shocks emit the observed gamma-rays by a
combination of synchrotron and inverse Compton emission. External shocks with
the circumstellar matter slow down further the ejecta and produce the
afterglow, which lasts for months. Comparison of the predictions of this
fireball model with observations confirm a relativistic macroscopic motion with
a Lorentz factor of . Breaks in the light curves of the
afterglow indicate that GRBs are beamed with typical opening angles of a few
degrees. The temporal variability of the gamma-rays signal provide us with the
best indirect evidence on the nature of the ``internal engine'' that powers the
GRBs and accelerates the relativistic ejecta, suggesting accretion of a massive
disk onto a newborn black hole: GRBs are the birth cries of these black holes.
Two of the most promising models: Neutron Star Mergers and Collapars lead
naturally to this scenario.Comment: Invited talk Texas Symposium, 12 page
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