2 research outputs found
Gamma-Ray Bursts and the Fireball Model
Gamma-ray bursts (GRBs) have puzzled astronomers since their accidental
discovery in the late sixties. The BATSE detector on the COMPTON-GRO satellite
has been detecting one burst per day for the last six years. Its findings have
revolutionized our ideas about the nature of these objects. They have shown
that GRBs are at cosmological distances. This idea was accepted with
difficulties at first. The recent discovery of an X-ray afterglow by the
Italian/Dutch satellite BeppoSAX has led to a detection of high red-shift
absorption lines in the optical afterglow of GRB970508 and in several other
bursts and to the identification of host galaxies to others. This has confirmed
the cosmological origin. Cosmological GRBs release ergs
in a few seconds making them the most (electromagnetically) luminous objects in
the Universe. The simplest, most conventional, and practically inevitable,
interpretation of these observations is that GRBs result from the conversion of
the kinetic energy of ultra-relativistic particles or possibly the
electromagnetic energy of a Poynting flux to radiation in an optically thin
region. This generic "fireball" model has also been confirmed by the afterglow
observations. The "inner engine" that accelerates the relativistic flow is
hidden from direct observations. Consequently it is difficult to infer its
structure directly from current observations. Recent studies show, however,
that this ``inner engine'' is responsible for the complicated temporal
structure observed in GRBs. This temporal structure and energy considerations
indicates that the ``inner engine'' is associated with the formation of a
compact object - most likely a black hole.Comment: A review - Latex, 59 pages including 29 figures. To appear in Physics
Report
The Physics of Gamma-Ray Bursts
Gamma-Ray Bursts (GRBs), short and intense pulses of low energy gamma-rays,
have fascinated astronomers and astrophysicists since their unexpected
discovery in the late sixties. During the last decade, several space missions:
BATSE (Burst and Transient Source Experiment) on Compton Gamma-Ray Observatory,
BeppoSAX and now HETE II (High-Energy Transient Explorer), together with ground
optical, infrared and radio observatories have revolutionized our understanding
of GRBs showing that they are cosmological, that they are accompanied by long
lasting afterglows and that they are associated with core collapse Supernovae.
At the same time a theoretical understanding has emerged in the form of the
fireball internal-external shocks model. According to this model GRBs are
produced when the kinetic energy of an ultra-relativistic flow is dissipated in
internal collisions. The afterglow arises when the flow is slowed down by
shocks with the surrounding circum-burst matter. This model has numerous
successful predictions like the prediction of the afterglow itself, the
prediction of jet breaks in the afterglow light curve and of an optical flash
that accompanies the GRBs themselves. In this review I focus on theoretical
aspects and on physical processes believed to take place in GRBs.Comment: 159 pages, 33 figures, accepted for publication in Reviews of Modern
Physic