Symposium Proceedings

WD Binaries and CV

X-ray Binaries in Terzan 5

C. O. Heinke (Northwestern Univ.), R. Wijnands (Univ. of Amsterdam), J. E. Grindlay (Harvard Univ.), H. N. Cohn, P. M. Lugger (Indiana Univ.), P. D. Edmonds (Harvard Univ.), D. Pooley (UC Berkeley), W. H. G. Lewin (MIT)

Terzan 5 is a dense metal-rich globular cluster, containing a transient LMXB and large numbers of millisecond pulsars and low-luminosity X-ray binaries. We present results from a Chandra survey of this globular cluster, focusing on the implications for the physical nature of the X-ray sources.

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Time-Resolved X-Ray Spectroscopy of EX Hydrae

Ronnie Hoogerwerf, Nancy Brickhouse (Harvard-Smithsonian Center for Astrophysics), Chris Mauche (LLNL)

EX Hydrae is the brightest Intermediate Polar type cataclysmic variable in the sky. The 60 ks DDT HETG observation of EX Hya yielded a high signal-to-noise spectrum that made it possible to measure the first x-ray radial velocity curve for a white dwarf and determine its mass independently from an accretion model. Furthermore, light curves versus the binary (97 min) and white dwarf (68 min) period revealed new features. The binary light curves require absorption by an ionized absorber whose charge state changes with binary phase. We rule out photoionization and interpret this charge state change as a temperature gradient in the accretion disk, perhaps from shocks. The white dwarf light curves for individual spectral lines formed at low temperatures (i.e. in the cool, low part of the accretion column) show sharp spikes. Using the standard model, we can derive the height above the white dwarf surface at which these lines are formed. These results demonstrate that, given sufficient signal-to-noise, X-ray spectroscopy will allow us to map the temperature and density structure of magnetic accretion columns.

Comparison of Chandra and XMM-Newton Observations of R Aqr

Edwin Kellogg, Craig Anderson, Joseph DePasquale, Kelly Korreck, Joy Nichols (SAO), Jeffrey Pedelty (NASA-GSFC), Jennifer Sokoloski (SAO)

X-ray and VLA radio observations of R Aqr over the past several years have revealed a rich variety of phenomena, in addition to observations spanning decades in radio, optical and IR. These observations argue more and more strongly for a binary system with a compact companion, with an accretion disk, producing jets along the symmetry axis of the compact object or accretion disk. Chandra observations at epochs 2000.7 and 2004.0 show bright regions of $10^6$ K thermal x-ray emission 1400-5000 AU out from the center, aligned with a bipolar axis extending from the star at PA $\sim$145°/325°. In the Chandra observations there is Fe K line emission, consistent with an unresolved source at the star, its compact companion, or an accretion disk. A recent XMM-Newton observation of R Aqr was taken in 2005.5. We report on further evolution of the jets and Fe K lines. We also report on XMM RGS high resolution grating spectroscopy, resolving $\sim 10^6$ K line emission in the jets. We also see evidence for emission at higher energies in the 7.5-12 keV range for the first time.

Chandra Observations of R Aquarii's Non-Relativistic Outer Jets

Kelly Korreck, Edwin Kellogg, Craig Anderson, Joe DePasquale, Joy Nichols, Jennifer Sokoloski (Harvard-Smithsonian Center for Astrophysics)

Two epochs of Chandra X-Ray observations of R Aquarii, combined with VLA radio data, reveal non-relativistic, evolving outer jets. The multi-wavelength spectral energy distribution indicates that the X-rays from the outer jet are thermal, in contrast with the inner jets, which are non-thermal (see Nichols et al, this conference). The outer-jet emission from both the northeast (NE) and southwest (SW) jets is compatible with shock heating of material ejected from the compact object in R Aquarii. The X-ray-bright region of the NE jet is moving outward with an apparent bulk velocity of 600 km/s, which is faster than the 150 km/s motion of the radio-bright portion of the jet. The jet in the NE is still a strong source of X-rays in the second epoch (2004.0), whereas the X-ray emission from the SW jet faded between 1999.8 and 2004.0. The disappearance of the southern outer X-ray jet is consistent with adiabatic expansion and cooling,implying a low density environment in the SW. New Chandra x-ray observations of the system will reveal greater details of the processes and environment driving the evolution of the outer jets.

[PDF of the poster]

Chandra Observations of the Core and Inner Jet of R Aqr

J. Nichols, J. Sokoloski, E. Kellogg, C. Anderson, J. DePasquale (Harvard-Smithsonian Center for Astrophysics)

R Aqr is a nearby jet-producing symbiotic binary-star system. Chandra spectra of the core of R Aqr reveal changes in the soft continuum, hard continuum, and Fe K lines on a time scale of years. The data also suggest possible rapid variability with a period of about 1700 sec in the Fe K lines. Such rapid variability must originate from very close to the wind-accreting white dwarf. The X-ray data also suggest that the accretion rate on the white dwarf in this system is variable. A new infant X-ray jet is identified in the Chandra data, and the power-law X-ray spectrum indicates that the emission from this new inner jet is non-thermal.

Long and Short Term Time Variability in Supersoft X-ray Sources

Marina Orio (INAF-Torino, Italy and Univ. of Wisconsin), Elia Leibowitz (Tel Aviv Univ., Israel), Alon Retter (Penn State Univ.), Emre Tepedelenlioglu (Physics Dept., Univ. of Wisconsin), Paola Mucciarelli (Dept. of Astronomy, Univ. of Padova, Italy)

Supersoft X-ray sources, likely progenitors of type Ia SN, are an intriguing class of objects but they are still poorly understood. They are often variable on time scales of years, months, hours and even seconds. In the framework of a funded Chandra archival program we searched the whole data base of X-ray observations of these sources. Long term variability may be due to three different types of evolutionary phenomena: a) thermonuclear flashes, b) a wind originated when more mass is accreted than the rate for stable hydrogen burning, or c) irradiation effects triggering variations in mass transfer rate from the secondary. Short term variability, typically on many-minutes time scales, may be due to non radial oscillations of the white dwarf, or to its spin. We classified the variability of the different systems in order to find clues to their physical nature.