Time Dependent Accretion Disk Models of GRS 1915+105
Sergei Nayakshin
Saul Rappaport
Abstract
During the past few years, the galactic microquasar GRS 1915+105 has
exhibited a bewildering diversity of large amplitude, chaotic
variability in X-rays. We show that the fast rises and falls in the
light curve of this source rule out an ADAF for this source. We argue
that observations clearly require a quasi-stable accretion disk
solution at high accretion rates. We have therefore devised a modified
viscosity law which has a quasi-stable upper branch, and developed a
code to solve the time-dependent equations for an accretion disk. The
model does indeed account for several of the gross observational
features of GRS 1915, including the overall cyclic behavior on
time-scales of ~ 100 - 1000 s, although a detailed comparison
fails.
We then consider several effects as a possible explanation for the
disagreement between the theory and the observations. A hot corona
above the disk, a radius dependent a-parameter, and advection
of energy into the hole do not appear to be promising in this
respect. However, a more elaborate model with a corona and a jet
is moderately successful in reproducing GRS 1915+105 behavior.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.