Partial accretion in the propeller stage of low mass X-ray binary Aql X--1
arXiv:1709.02378 · doi:10.3847/1538-4357/aa8b76
Abstract
Aql X--1 is one of the most prolific low mass X-ray binary transients (LMXBTs) showing outbursts almost annually. We present the results of our spectral analyses of RXTE/PCA observations of the 2000 and the 2011 outbursts. We investigate the spectral changes related to the changing disk-magnetosphere interaction modes of Aql X--1. The X-ray light curves of the outbursts of LMXBTs typically show phases of fast rise and exponential decay. The decay phase shows a "knee" where the flux goes from the slow decay to the rapid decay stage. We assume that the rapid decay corresponds to a weak propeller stage at which a fraction of the inflowing matter in the disk accretes onto the star. We introduce a novel method for inferring, from the light curve, the fraction of the inflowing matter in the disk that accretes onto the NS depending on the fastness parameter. We determine the fastness parameter range within which the transition from the accretion to the partial propeller stage is realized. This fastness parameter range is a measure of the scale-height of the disk in units of the inner disk radius. We applied the method to a sample of outbursts of Aql X--1 with different maximum flux and duration times. We show that different outbursts with different maximum luminosity and duration follow a similar path in the parameter space of accreted/inflowing mass flux fraction versus fastness parameter.
16 pages, 5 figures, 5 tables, accepted for publication in ApJ
References in corpus (10)
- X-ray Properties of Black-Hole Binaries
- Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
- Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
- "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
- Discovery of coherent millisecond X-ray pulsations in Aql X-1
- The return to quiescence of Aql X-1 following the 2010 outburst
- Outburst Morphology in the Soft X-ray Transient Aquila X-1
- Modeling of non-stationary accretion disks in X-ray novae A 0620-00 and GRS 1124-68 during outburst
- The Vela Pulsar With an Active Fallback Disk
- Non-Steady State Accretion Disks in X-Ray Novae: Outburst Models for Nova Monocerotis 1975 and Nova Muscae 1991