Short-term pulse frequency fluctuations of OAO 1657-415 from RXTE observations

We present new X-ray observations of the high-mass X-ray binary (HMXRB) pulsar OAO 1657-415, obtained during one orbital period (10.44 d) with the Rossi X-Ray Timing Explorer (RXTE). Using the binary orbital parameters, obtained from Burst and Transient Source Experiment (BATSE) observations, we resolve the fluctuations in the pulse frequency at time-scales on the order of 1 d for the first time. Recent BATSE results by Baykal showed that OAO 1657-415 has spin-up/down trends in its pulse frequency time series, without any correlation with the X-ray luminosity at energies > 20 keV. In the present RXTE observations the source is found to be in an extended phase of spin-down. We also find a gradual increase in the X-ray luminosity which is correlated with a marginal spin-up episode. The marginal correlation between the gradual spin-up (or decrease in spin-down rate) and increase in X-ray luminosity suggests that OAO 1657-415 is observed during a stable accretion episode where the prograde accretion disc is formed.


The steady spin-down rate of 4U 1907+09
Baykal, Altan; Alpar, MA; Zand, JI; Strohmayer, T (2001-11-11)
Using X-ray data from the Rossi X-ray Timing Explorer, we report the pulse timing results of the accretion-powered, high-mass X-ray binary pulsar 4U 1907 + 09, covering a time-span of almost two years. We measured three new pulse periods in addition to the previously measured four pulse periods. We are able to connect pulse arrival times in phase for more than a year. The source has been spinning down almost at a constant rate, with a spin-down rate of (nu) over dot = (- 3.54 +/- 0.02) x 10(-14) Hz s(-1) fo...
Spin-down rate of 1E 2259+586 from RXTE observation
Baykal, Altan; Strohmayer, T; Stark, MJ (1998-08-01)
We present new X-ray observations of the X-ray pulsar 1E 2259+586, obtained during March 1997, with the Rossi X-Ray Timing Explorer (RXTE). We have measured the pulse frequency derivative (nu) over dot = (-1.08 +/- 0.04) x 10(-14) Hz s(-1) from pulse arrival times obtained in a sequence of 5 observations spread over one month. This (nu) over dot is consistent with the long term spin-down trend. We also found that the observed X-ray luminosity is consistent with that measured at quiescent X-ray flux levels b...
RXTE timing analysis of the anomalous X-ray pulsar 1E 2259+586
Icdem, B.; Baykal, Altan; İNAM, SITKI ÇAĞDAŞ (2012-02-01)
We present a pulse-timing analysis of Rossi X-ray Timing Explorer (RXTE) observations of the anomalous X-ray pulsar 1E 2259+586 from its 2002 outburst to 2010 October. We have the following objectives: to extend the work on the recovery stage after the 2002 glitch; to investigate the variations caused by the second glitch that occurred in 2007; to look for other unusual events, if any, that arise in the regular spin-down trend of the source. We find that the fractional change in the spin frequency derivativ...
Spin down and oscillations in 4U 1907+09: a retrograde disk?
Zand, JJMI; Strohmayer, TE; Baykal, Altan (1999-01-01)
X-ray observations of the accretion-powered X-ray pulsar 4U 1907+09, obtained during February 1996 with the Proportional Counter Array on the Rossi X-ray Timing Experiment (RXTE), have shown interesting features of which three are: 1) a flare occurred lasting at least a few hours and close to the time of apastron; 2) the spin down rate, when measured since the pulsar discovery in 1983, is within 8% equal to a value of (P)over dot(pulse) = +0.225 s yr(-1), this suggest that the pulsar is in a monotonous spin...
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...
Citation Formats
A. Baykal, “Short-term pulse frequency fluctuations of OAO 1657-415 from RXTE observations,” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, pp. 637–640, 2000, Accessed: 00, 2020. [Online]. Available: