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Title: GIANT OUTBURSTS IN Be/X-RAY BINARIES

Be/X-ray binary systems exhibit both periodic (Type I) X-ray outbursts and giant (Type II) outbursts, whose origins have remained elusive. We suggest that Type II X-ray outbursts occur when a highly misaligned decretion disk around the Be star becomes eccentric, allowing the compact object companion to capture a large amount of material at periastron. Using three-dimensional smoothed particle hydrodynamics simulations, we model the long-term evolution of a representative Be/X-ray binary system. We find that periodic (Type I) X-ray outbursts occur when the neutron star is close to periastron for all disk inclinations. Type II outbursts occur for large misalignment angles and are associated with eccentricity growth which occurs on a timescale of about 10 orbital periods. Mass capture from the eccentric decretion disk results in an accretion disk around the neutron star whose estimated viscous time is long enough to explain the extended duration of Type II outbursts. Previous studies suggested that the outbursts are caused by a warped disk but our results suggest that this is not sufficient; the disk must be both highly misaligned and eccentric to initiate a Type II accretion event.
Authors:
; ;  [1] ;  [2] ;  [3]
  1. JILA, University of Colorado and NIST, UCB 440, Boulder, CO 80309 (United States)
  2. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  3. Monash Centre for Astrophysics (MoCA), School of Mathematical Sciences, Monash University, Victoria 3800 (Australia)
Publication Date:
OSTI Identifier:
22365433
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; CAPTURE; COMPUTERIZED SIMULATION; COSMIC PHOTONS; HYDRODYNAMICS; MASS; NEUTRON STARS; PERIODICITY; STAR EVOLUTION; THREE-DIMENSIONAL CALCULATIONS; X RADIATION