Extended Emission from Cygnus X-3 Detected with Chandra

We have discovered extended X-ray emission from the microquasar Cyg X-3 in archival Chandra X-ray Observatory observations. A 5" wide structure lies approximately 16" to the NE from the core point source and may be extended in that direction. This angular scale corresponds to a physical extent of roughly 0.8 lyr, at a distance of 2.5 lyr from Cyg X-3 (assuming a 10 kpc distance). The flux varied by a factor of 2.5 during the four months separating two of the observations, indicating significant substructure. The peak 2-10 keV luminosity was about 5e34 ergs/s. There may also be weaker, extended emission of similar scale oppositely directed from the core, suggesting a bipolar outflow. This structure is not part of the dust scattering halo, nor is it caused by the Chandra point spread function. In this Letter we describe the observations and discuss possible origins of the extension.Comment: Submitted to ApJ Letters. 5 pages, 2 figures (1 color). Uses emulateap

XMM-Newton Observations of the Be/X-ray transient A0538-66 in quiescence

We present XMM-Newton observations of the recurrent Be/X-ray transient A0538-66, situated in the Large Magellanic Cloud, in the quiescent state. Despite a very low luminosity state of (5-8)E33 ergs/s in the range 0.3-10 keV, the source is clearly detected up to ~8 keV. and can be fitted using either a power law with photon index alpha=1.9+-0.3 or a bremsstrahlung spectrum with kT=3.9+3.9-1.7 keV. The spectral analysis confirms that the off-state spectrum is hard without requiring any soft component, contrary to the majority of neutron stars observed in quiescence up to now.Comment: Accepted for proceedings of 5th INTEGRAL Worksho

RXTE Observations of LMC X-1 and LMC X-3

Of all known persistent stellar-mass black hole candidates, only LMC X-1 and LMC X-3 consistently show spectra that are dominated by a soft, thermal component. We present results from long (170ksec) Rossi X-ray Timing Explorer (RXTE) observations of LMC X-1 and LMC X-3 made in 1996 December. The spectra can be described by a multicolor disk blackbody plus an additional high-energy power-law. Even though the spectra are very soft (Gamma is about 2.5), RXTE detected a significant signal from LMC X-3 up to energies of 50keV, the hardest energy at which the object was ever detected. Focusing on LMC X-3, we present results from the first year of an ongoing monitoring campaign with RXTE which started in 1997 January. We show that the appearance of the object changes considerably over its ~200d long cycle. This variability can either be explained by periodic changes in the mass transfer rate or by a precessing accretion disk analogous to Her X-1.Comment: 4 pages, 5 figures, also available at http://aitzu3.ait.physik.uni-tuebingen.de/publications/preprints1998.html to be published in "Highlights of X-Ray Astronomy, a symposium in honour of Joachim Truemper" (B. Aschenbach et al., eds.), MPE Repor

Monitoring the Short-Term Variability of Cyg X-1: Spectra and Timing

We present first results from the spectral and temporal analysis of an RXTE monitoring campaign of the black hole candidate Cygnus X-1 in 1999. The timing properties of this hard state black hole show considerable variability, even though the state does not change. This has previously been noted for the power spectral density, but is probably even more pronounced for the time lags. From an analysis of four monitoring observations of Cyg X-1, separated by 2 weeks from each other, we find that a shortening of the time lags is associated with a hardening of the X-ray spectrum, as well as with a longer characteristic ``shot time scale''. We briefly discuss possible physical/geometrical reasons for this variability of the hard state properties.Comment: 5 pages, 2 figures, Proc. of the 5th Compton Symposium, AIP, in pres

Energetics and dynamics of simple impulsive solar flares

Flare energetics and dynamics were studied using observations of simple impulsive spike bursts. A large, homogeneous set of events was selected to enable the most definite tests possible of competing flare models, in the absence of spatially resolved observations. The emission mechanisms and specific flare models that were considered in this investigation are described, and the derivations of the parameters that were tested are presented. Results of the correlation analysis between soft and hard X-ray energetics are also presented. The ion conduction front model and tests of that model with the well-observed spike bursts are described. Finally, conclusions drawn from this investigation and suggestions for future studies are discussed