Black-Hole Binaries As Relics Of Long-Soft Gamma-Ray Burst And Hypernova Explosions
Enrique Moreno-Mendez
State University of New York
The Collapsar model, in which a fast-spinning massive star collapses into
a Kerr black hole, has become the standard model to explain long-soft
gamma-ray bursts and hypernova explosions (GRB/HN), however, stars
massive enough (those with ZAMS mass larger than some 18 to 20 solar
masses) to produce these events evolve through a path that loses too much
angular momentum as to produce a central engine capable of delivering the
necessary energy. In this work we study the soft X-ray transient sources
as the remnants of GRBs/HNe; that is, binaries in which, as the massive
primary star evolves a carbon-oxygen burning core, it starts transferring
material to the secondary star (Case C mass transfer), shrinking the
orbit until a common-envelope evolution sets in and the secondary spirals
in, further narrowing the orbit of the binary and removing the hydrogen
envelope of the primary star; eventually the primary star becomes tidally
locked and gets spun up acquiring enough rotational energy to power up
a GRB/HN explosion. The central engine producing the GRB/HN event being
the Kerr black hole through the Blandford-Znajek mechanism.
It turns out that our model can explain not only the long-soft GRBs,
but also: The subluminous bursts, which comprise about 97% of the total,
the bursts of cosmological energy and the short-hard bursts (in a neutron
star, black hole merger). Because of our binary evolution through Case
C mass transfer, it turns out that for the subluminous and cosmological
bursts, the angular momentum is proportional to the mass of the secondary
star to the 3/2 power. This gives the binary evolution a great advantage
over the Woosley Collapsar model; namely, that one can "dial" the donor
mass in order to achieve whatever angular momentum is needed to drive
the explosion.
Population syntheses show that there are enough binaries to account for
the progenitors of all classes of GRBs.
Date: | Lundi, le 1 décembre 2008 |
Heure: | 12:00 |
Lieu: | Université McGill |
| Ernest Rutherford Physics Building, room 326 |
|