Browsing by Author "Balman, Şölen"

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Accretion Flows in Nonmagnetic White Dwarf Binaries as Observed in X-Rays By:balman, S (balman, Solen)[ 1 ]
(Elsevıer Scı Ltd, 2020) Balman, Şölen
Cataclysmic Variables (CVs) are compact binaries with white dwarf (WD) primaries. CVs and other accreting WD binaries (AWBs) are useful laboratories for studying accretion flows, gas dynamics, outflows, transient outbursts, and explosive nuclear burning under different astrophysical plasma conditions. They have been studied over decades and are important for population studies of galactic X-ray sources. Recent space-and ground-based high resolution spectral and timing studies, along with recent surveys indicate that we still have observational and theoretical complexities yet to answer. I review accretion in nonmagnetic AWBs in the light of X-ray observations. I present X-ray diagnostics of accretion in dwarf novae and the disk outbursts, the nova-like systems, and the state of the research on the disk winds and outflows in the nonmagnetic CVs together with comparisons and relations to classical and recurrent nova systems, AM CVns and Symbiotic systems. I discuss how the advective hot accretion flows (ADAF-like) in the inner regions of accretion disks (merged with boundary layer zones) in nonmagnetic CVs explain most of the discrepancies and complexities that have been encountered in the X-ray observations. I stress how flickering variability studies from optical to X-rays can be probes to determine accretion history and disk structure together with how the temporal and spectral variability of CVs are related to that of LMXBs and AGNs. Finally, I discuss the nature of accretion in nonmagnetic WDs in terms of ADAF-like accretion flows, and elaborate on the solu-tions it brings and its complications, constructing an observational framework to motivate new theoretical calculations that introduce this flow-type in disks, outflow and wind models together with disk-instability models of outbursts and nova outbursts in AWBs and WD physics, in general. (C) 2020 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords
Preface: Nova Eruptions, Cataclysmic Variables and Related Systems: Challenges in the 2020 Era
(Elsevier, 2020) Balman, Şölen
[Abstract Not Available]
The Ulx Source X-3 in Ngc 4258: a Search for Its X-Ray and Optical Properties
(Oxford Univ Press, 2020) Akyüz, Aysun; Avdan, Şenay; Allak, Sinan; Aksaker, Nazım; Oralhan, İnci Akkaya; Balman, Şölen
We present the results of a search for the nature of ultraluminous X-ray source (ULX) X-3 in the nearby galaxy NGC 4258. We use archival data from XMM-Newton, Chandra, NuSTAR, and Hubble Space Telescope (HST) observations. Total X-ray data were analysed to find that the model parameters of the system are indicative of a stellar-mass black hole, similar to 10 M-circle dot, as the central compact object. Furthermore, analyses of the optical data from HST reveal two optical candidates at 90 per cent confidence level within an error radius of 0.28 arcsec. Assuming the optical emission is dominated by the donor star, both of these candidates are found to have spectral types that lie between B3 and F1 with absolute magnitudes of M-V approximate to -6.4. Moreover, the age and mass estimates for the candidates are found to be 10 and 18 Myr and 13 and 20 M-circle dot, respectively.