The central region of M31 has been monitored with Chandra > 120 times over the last 11 years. In this region we find X-ray sources corresponding to 35 out of 420 globular clusters; these are highly likely to be X-ray binaries. We have created long-term, calibrated lightcurves for all 35 sources, and will present highlights of our variability survey

We report on optical observations of the field of the black hole candidate X-ray binary MAXI J1543-564 (ATel #3330, #3331, #3334, #3336, #3341, #3355) with the 2-m Faulkes Telescope South (located at Siding Spring, Australia). Three images were acquired in SDSS i'-band on 2011 May 11th, 14th and 15th (MJD 55692.585, 55695.757 and 55696.752)

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Only a few binary systems with compact objects display TeV emission. The physical properties of the companion stars represent basic input for understanding the physical mechanisms behind the particle acceleration, emission, and absorption processes in these so-called gamma-ray binaries. Here we present high-resolution and high signal-to-noise

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We investigate the origin and physical properties of O VI absorbers at low redshift (z= 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening O VI absorbers are believed to trace shock-heated gas in the warm-hot intergalactic medium (WHIM) and may thus play a key role