INTEGRAL observations of the variability of OAO 1657-415

Abstract

The Galactic Plane Scan (GPS) was one of the core observation programmes of the INTEGRAL satellite. The highly variable accreting pulsar OAO 1657-415 was frequently observed within the GPS. We investigate the spectral and timing properties of OAO 1657-415 and their variability on short and long time scales in the energy range 6-160 keV. During the time covered by the INTEGRAL observations, the pulse period evolution shows an initial spin-down, which is followed by an equally strong spin-up. In combining our results with historical pulse period measurements (correcting them for orbital variation) and with stretches of continuous observations by BATSE, we find that the long-term period evolution is characterised by a long-term spin-up overlayed by sets of relative spin-down/spin-up episodes, which appear to repeat quasi-periodically on a 4.8 yr time scale. We measure an updated local ephemeris and confirm the previously determined orbital period with an improved accuracy. The spectra clearly change with pulse phase. The spectrum measured during the main peak of the pulse profile is particularly hard. We do not find any evidence of a cyclotron line, wether in the phase-averaged spectrum or in phase-resolved spectra.

12 pages, 11 figures

References in corpus (2)

• 4U 0115+63 from RXTE and INTEGRAL Data: Pulse Profile and Cyclotron Line Energy
• INTEGRAL observation of the accreting pulsar GX 1+4

Cited by in corpus (16)

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• XMM-Newton spectroscopy of the accreting magnetar candidate 4U0114+65
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• Properties and observability of glitches and anti-glitches in accreting pulsars
• Timing and Spectral Analysis of HMXB OAO 1657-415 with NuSTAR
• Multitude of iron lines including a Compton scattered component in OAO 1657--415 detected with Chandra
• A NuSTAR observation of the eclipsing binary system OAO 1657-415: The revival of the cyclotron line
• Torque reversal and orbital profile of X-ray pulsar OAO 1657-415
• Timing and spectral studies of Cen X-3 in multiple luminosity states using $\text{AstroSat}$
• Variability study of the High Mass X-ray Binary IGR J18027--2016 with {\it Swift}--XRT
• AstroSat observations of eclipsing high mass X-ray binary pulsar OAO 1657-415
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415
• On the origin of super-global spin-up trends of X-ray pulsars in HMXB systems