Baykal, Altan
We calculate the power density spectrum of fluctuations in the X-ray turn-on times of Her X-1, including new data which extend the X-ray and optical flux observations to a span of over 20 yr with 221 distinct 35-d high-low flux cycles. If we assume that turn-on times define the period of the 35-d clock, this statistical interpretation of turn-on behaviour is consistent with a white-noise process in the first derivative of the 35-d phase fluctuations (or a random walk in clock phase). We discuss the implications of considering the 35-d clock mechanism as a noise process.


Low frequency flickering of TT Arietis: Hard and soft X-ray emission region
Baykal, Altan (1997-01-01)
Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures similar to 1 keV and similar to 10 keV. A coherent feature at similar to 0.643 mHz appeared in the power spectra during the observation.
The re-analysis of the ROSAT data of Nova Mus 1983 using white dwarf atmosphere emission models
Balman, Şölen; Krautter, J (2001-10-01)
The analyses of X-ray emission from classical novae during the outburst stage have shown that the soft X-ray emission below 1 keV, which is thought to originate from the photosphere of the white dwarf, is inconsistent with the simple blackbody model of emission. Thus, ROSAT Position Sensitive Proportional Counter (PSPC) archival data of the classical Nova Mus 1983 (GQ Mus) have been re-analysed in order to understand the spectral development in the X-ray wavelengths during the outburst stage. The X-ray spec...
The broad-band noise characteristics of selected cataclysmic variables (CVS), anomalous x-ray pulsars (AXPS) and soft gamma repeaters (SGRS)
Külebi, Baybars; Balman, Şölen; Department of Physics (2006)
In this work present the broad-band noise structure in the 2-60 keV data of Cataclysmic Variables (CVs) with Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs). We analyzed Rossi X-ray Timing Explorer (RXTE) PCA data and derived time series from 27 CVs, 4 AXPs and 1 SGR using the RXTE archive. In general, CVs of different types all show broad band noise which can be fitted with power laws, using exponentional cut-offs, and Lorentzians in a similar way to power spectral (noise) characteristics of...
The torque and X-ray flux changes of OAO 1657-415
Baykal, Altan (1997-03-01)
Combining previously published pulse frequencies and BATSE measurements, we estimate the noise strengths (or power density estimates) of angular accelerations by using the root mean square residuals of angular velocity time series of OAO 1657-415 and present the power spectra. The statistical interpretation of the angular velocity fluctuations is consistent with a random walk model. In order to investigate the short term angular velocity fluctuations in detail, a structure function analysis is applied for a...
Orbital Phase Resolved Spectroscopy of EX Hya Using XMM-NEWTON
Pekon, Yakup; Balman, Şölen (2009-09-11)
We present for the first orbital phase resolved spectra of intermediate polar (IP), EX Hya, during two different states with a factor of 3 difference between the X-ray count rates. We find definite spectral variations between different states of the source. The adopted model is composed of two MEKAL plus a VMCFLOW components to account for the continuum which is partially absorbed. Additional Gaussian lines at energies similar to 6,4, 6.7 and 6.9 keV were also included to fit the residuals. The soft compone...
Citation Formats
A. Baykal, J. DEETER, and D. SCOTT, “THE NOISE IN THE 35-D CYCLE OF HER X-1,” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, pp. 347–350, 1993, Accessed: 00, 2020. [Online]. Available: