Spin up in RX J0806+15 - the shortest period binary

Abstract

RX J0806+15 has recently been identified as the binary system with the shortest known orbital period. We present a series of observations of RX J0806+15 including new optical observations taken one month apart. Using these observations and archival data we find that the period of this system is decreasing over time. Our measurements imply f_dot = 6.11x10^-16 Hz/s, which is in agreement with a rate expected from the gravitational radiation for two white dwarfs orbiting at a given period. However, a smaller value of f_dot = 3.14x10^-16 Hz/s cannot be ruled out. Our result supports the idea that the 321.5 s period is the orbital period and that the system is the shortest period binary known so far and that it is one of the strongest sources of constant gravitational radiation in the sky. Furthermore, the decrease of the period strongly favours the unipolar inductor (or electric star) model rather than the accretion models.

5 pages, 4 figures, accepted for publication in MNRAS letters

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• Evolution of Close White Dwarf Binaries
• Long-term X-ray variability of Swift J1644+57
• Electron-cyclotron maser emission from white-dwarf pairs and white-dwarf planetary systems
• Precision X-ray Timing of RX J0806.3+1527 with CHANDRA: Evidence for Gravitational Radiation from an Ultracompact Binary
• Face-on, stream-fed intermediate polars: an alternative model for RX J1914.4+2456 and RX J0806.3+1527
• CHANDRA Observations of V407 Vul: Confirmation of the Spin-up
• ULTRACAM Photometry of the ultracompact binaries V407 Vul and HM Cnc
• XMM-Newton observations of the ultra-compact binary RX J1914+24
• Unveiling the Nature of the 321 s Modulation in RX J0806.3+1527: Near-Simultaneous Chandra and VLT Observations
• The Turn-On of Mass Transfer in AM CVn Binaries: Implications for RX J0806+1527 and RX J1914+2456
• Two decades of optical timing of the shortest-period binary star system HM Cancri
• Period Changes in Ultra-compact Double White Dwarfs
• Geometrical constraints upon the unipolar model of V407 Vul and RXJ0806.3+1527
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• CHANDRA Detection of the AM CVn binary ES Cet (KUV 01584-0939)
• The photometric period in ES Ceti
• SPH Simulations of Direct Impact Accretion in the Ultracompact AM CVn Binaries
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