The torque and X-ray flux changes of OAO 1657-415

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 two component neutron star model with a solid crust and a superfluid neutron core which is subjected to external white torque noise. No evidence for core-crust coupling on timescales longer than one day is found. The correlations between X-ray flux and angular acceleration (Omega over dot) fluctuations are investigated. These are compared with disk accretion theory (Ghosh & Lamb 1979 a,b) and wind accretion theory (Blondin et al., 1990). It is found that the most natural explanation of X ray flux and angular acceleration fluctuations is the formation of episodic accretion disks in the case of stellar wind accretion.


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...
X-ray flux and pulse frequency changes of three high mass X-ray binary pulsars: Vela X-1, GX 301-2 and OAO 1657-415
Inam, SC; Baykal, Altan (2000-01-01)
Using archival BATSE (Burst and Transient Source Experiment) 20-50 keV band X-ray flux and pulse frequency time series, we look for correlations between torque, luminosity and specific angular momentum for three high mass X-ray binary pulsars Vela X-1, GX 301-2 and OAO 1657-415. Our results show that there is no correlation between pulse frequency derivative and flux which may be an indication of the absence of stable prograde accretion disk. From the strong correlation of specific angular momentum and torq...
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 AXPs and SGRs: Probing the magnetar coronae
Kulebi, Baybars; Balman, Şölen (2007-08-17)
We present the broad-band noise structure of Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) in the 2-60 keV energy band which are thought to be powered by either magnetic decay(Thompson & Duncan 1995) or accretion (Alpar 2001). We have used Rossi X-ray Timing Explorer (R-XTE) PCA archival light curves and derived time series for 4 AXPs and 1 SGR. We detect that AXP and SGR sources show band limited noise at low frequencies in the range 0.005-0.05 Hz. We find that this noise level can be asso...
Baykal, Altan; DEETER, JE; SCOTT, DM (1993-11-15)
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 implicat...
Citation Formats
A. Baykal, “The torque and X-ray flux changes of OAO 1657-415,” ASTRONOMY & ASTROPHYSICS, pp. 515–524, 1997, Accessed: 00, 2020. [Online]. Available: