2009/08/01 by D. Klochkov, R. Staubert, K. Postnov +2 · 1 citation
Physics and Astronomy · #Accretion (finance) #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Flux (metallurgy) #Light curve #Luminosity #Magnetosphere #Neutron star #Orbital period #Pulsar #Pulse (music) #Scientific Research and Discoveries #astro-ph.HE
paper · pdf · doi:10.1051/0004-6361/200912791
7 pages, 5 figures, accepted for publication in Astronomy & Astrophysics
arxiv created 2009/08/01 · openalex publication_date 2009/08/27 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
<i>Context. <i/>Monitoring of pulse period variations in accreting binary pulsars is an important tool to study the interaction between the magnetosphere of the neutron star and the accretion disk. While the X-ray flux of the brightest X-ray pulsars have been successfully monitored over many years (e.g. with <i>RXTE/ASM, CGRO/BATSE, Swift/BAT<i/>), the possibility to monitor their pulse timing properties continuously has so far been very limited.<i>Aims. <i/>In our work we show that the <i>Swift/BAT<i/> observations can be used to monitor coherent pulsations of bright X-ray sources and use <i>Swift<i/> archival data to study one of the most enigmatic X-ray pulsars, Hercules X-1. A quasi-continuous monitoring of the pulse period and the pulse period derivative of an X-ray pulsar, here Her X-1, is achieved over a long time (<i>≳<i/>4 yr). We compare our observational results with predictions of accretion theory and use them to test different aspects of the physical model of the system.<i>Methods. <i/>In our analysis we use the data accumulated with <i>Swift/BAT<i/> starting from the beginning of 2005 (shortly after launch) until the present time. To search for pulsations and for their subsequent analysis we used the count rate measured by the <i>BAT<i/> detector in the entire field of view.<i>Results. <i/>The slope of the correlation between the locally determined spin-up rate and the X-ray luminosity is measured for Her X-1 and found to be in agreement with predictions of basic accretion torque theory. The observed behaviour of the pulse period together with the previously measured secular decrease of the system's orbital period is discussed in the framework of a model assuming ejection of matter close to the inner boundary of the accretion disk.