2004/03/26 by M. Still, P. Boyd · 3 citations
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Accretion disc #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Earth Systems and Cosmic Evolution #Ephemeris #Millisecond pulsar #Precession #Pulsar #Telescope #astro-ph
paper · pdf · doi:10.1086/421349
published as Astrophys.J. 606 (2004) L135-L138 · 9 pages, 4 figures, ApJL in press
arxiv created 2004/03/26 · openalex publication_date 2004/04/15 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Rossi X-Ray Timing Explorer all-sky monitor count rates from the X-ray pulsar Her X-1 began falling consistently during the late months of 2003. The source is undergoing another state transition similar to the anomalous low state of 1999. This new event has triggered observations from both space- and ground-based observatories. In order to aid data interpretation and telescope scheduling and to facilitate the phase connection of cycles before and after the state transition, we have recalculated the precession ephemeris using cycles over the last 3.5 yr. We report that the source has displayed a different precession period since the last anomalous event. Additional archival data from the Compton Gamma Ray Observatory suggests that each low state is accompanied by a change in precession period and that the subsequent period is correlated with accretion flux. Consequently our analysis reveals long-term accretion disk behavior that is predicted by theoretical models of radiation-driven warping.