arXiv subjects

A. Tuncer

Publications and source records attributed to A. Tuncer.

3 recordsLinked to original sources

arXiv2021

A Minimal Timescale for the Continuum in 4U 1608-52 and Aql X-1

Similar to black-hole X-ray binary (BHXRB) transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries (NSXRBs). Using a method based on wavelets and lightcurves constructed from archival RXTE observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.

astro-ph.HE↗

arXiv2020

A Minimal Time Scale for the Spectral States of GX 339-4

Black hole transients are known to undergo spectral transitions that form q-shaped tracks on a hardness intensity diagram. In this work, we use archival RXTE data to extract a characteristic minimal timescale for the spectral states in GX 339-4 for the 2002-3, and 2010 outbursts. We use the extracted timescale to construct an intensity variability diagram for each outburst. This new diagram is comparable to the traditional hardness intensity diagram and offers the potential for probing the underlying dynamics associated with the evolution of the relevant emission regions in black hole transients. We confirm this possibility by connecting the minimal timescale with the inner disk radius, $R_{in}$ (estimated from spectral fits), and demonstrate a positive correlation between these variables as the system evolves through its spectral transitions. Furthermore, we probe the relation between the minimal timescale and the break frequencies extracted from the power spectral densities. Lastly, we examine a possible link between the extracted timescale and a traditional measure of variability i.e., the root mean square, determined directly from the power spectra.

astro-ph.HE↗

arXiv2007

Phase Diagrams and Crossover in Spatially Anisotropic d=3 Ising, XY Magnetic and Percolation Systems: Exact Renormalization-Group Solutions of Hierarchical Models

Hierarchical lattices that constitute spatially anisotropic systems are introduced. These lattices provide exact solutions for hierarchical models and, simultaneously, approximate solutions for uniaxially or fully anisotropic d=3 physical models. The global phase diagrams, with d=2 and d=1 to d=3 crossovers, are obtained for Ising, XY magnetic models and percolation systems, including crossovers from algebraic order to true long-range order.

cond-mat.stat-mech↗