SIMBAD references

RX J0806.3+1527 is a candidate double-degenerate binary with possibly the shortest known orbital period. The source shows an ~100% X-ray intensity modulation at the putative orbital frequency of 3.11 mHz (321.5 s). If the system is a detached, ultracompact binary, gravitational radiation should drive spin-up with a magnitude of ν{dot}∼10^–16 Hz/s. Efforts to constrain the X-ray frequency evolution to date have met with mixed success, principally due to the sparseness of earlier observations. Here we describe the results of the first phase-coherent X-ray monitoring campaign on RX J0806.3+1527 with Chandra. We obtained a total of 70 ks of exposure in six epochs logarithmically spaced over 320 days. With these data we conclusively show that the X-ray frequency is increasing at a rate of (3.77±0.8)x10^–16 Hz/s. Using the ephemeris derived from the new data, we are able to phase up all the earlier Chandra and ROSAT data and show that they are consistent with a constant ν{dot}=(3.63±0.06)x10^–16 Hz/s over the past decade. This value appears consistent with that recently derived by Israel et al., largely from monitoring of the optical modulation, and is in rough agreement with the solutions reported initially by Hakala et al., based on ground-based optical observations. The large and stable ν{dot} over a decade is consistent with gravitational radiation losses driving the evolution. An intermediate polar (IP) scenario in which the observed X-ray period is the spin period of an accreting white dwarf appears less tenable because the observed ν{dot} requires an m{dot}~2x10^–8M_☉/yr, which is much larger than that inferred from the observed X-ray luminosity (although this depends on the uncertain distance and bolometric corrections), and it is difficult to drive such a high m{dot} in a binary system with parameters consistent with all the multiwavelength data. If the ultracompact scenario is correct, then the X-ray flux cannot be powered by stable accretion, which would drive the components apart, suggesting that a new type of energy source (perhaps electromagnetic) may power the X-ray flux.