Discovery of Rapid Hard X‐Ray Variability and New Jet Activity in the Symbiotic Binary R Aquarii

Two Chandra observations of the R Aqr symbiotic binary system taken 3.3 yearsapart show dramatic changes in the X-ray morphology and spectralcharacteristics in the inner 500 AU of this system. The morphology of the softX-ray emission has evolved from a nearly circular region centered on the binarysystem to an hourglass shape that indicates the formation of a new southwestjet. Synchrotron radiation from the new jet in contemporaneous VLA radiospectra implies the physical conditions in the early stages of jet developmentare different from those in the more extended outer thermal jets known to existfor decades in this system. The central binary source has two X-ray spectralcomponents in each of the two epochs, a soft component and a highly absorbedhard component characterized by T ~ 10^8 K if fit with a thermal plasma model.The spectrum hardened considerably between 2000.7 and 2004.0, primarily due toincreased flux above 5 keV, suggesting a change in the accretion activity ofthe white dwarf on a timescale of a few years or less. Point-source Fe Kemission is detected at the position of the central binary system in bothobservations. While the earlier observation shows evidence of only a singleemission peak near Fe K alpha at 6.4 keV, the later observation shows a morecomplex emission structure between 6 and 7 keV. Finally, we have discovered amodulation in the hard X-ray flux with a period of 1734 s at a 95% confidencelevel in the 2004 observation only. The modulation potentially arises fromstanding shocks in an accretion column and we have explored the possibilitythat the white dwarf in R Aqr is analogous to the magnetic white dwarfs inIntermediate Polar.Comment: 31 pages, 14 figures, 1 table To be published in ApJ, expected April 10 issue. AAS LaTex styl