B. Aschenbach

Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre

Recent measurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* (refs 4, 5) at the Galactic Centre is a 3.6-million-solar-mass black hole. Sgr A* is remarkably faint in all wavebands other than the radio region, however, which challenges current theories of matter accretion and radiation surrounding black holes. The black holes rotation rate is not known, and therefore neither is the structure of space-time around it. Here we report high-resolution infrared observations of Sgr A* that reveal ‘quiescent’ emission and several flares. The infrared emission originates from within a few milliarcseconds of the black hole, and traces very energetic electrons or moderately hot gas within the innermost accretion region. Two flares exhibit a 17-minute quasi-periodic variability. If the periodicity arises from relativistic modulation of orbiting gas, the emission must come from just outside the event horizon, and the black hole must be rotating at about half of the maximum possible rate.

The ROSAT all - sky survey bright source catalogue

In order to ensure the quality of the source catalogue derived from the SASS processing an automatic as well as a visual screening procedure was applied to 1378 survey fields. Most (94%) of the 18,811 sources were confirmed by this screening process. The rest is flagged for various reasons. Broad band images are available for a subset of the flagged sources. Details of the screening process can be found at www.rosat.mpe-garching.mpg.de/survey/rass-bsc/doc.html.

RX J0852.0–4622: Another Nonthermal Shell-Type Supernova Remnant (G266.2–1.2)

The newly discovered supernova remnant G266.2-1.2 (RX J0852.0-4622), along the line of sight to the Vela supernova remnant (SNR), was observed with ASCA for 120 ks. We find that the X-ray spectrum is featureless and well described by a power law, extending to three of the class of shell-type SNRs dominated by nonthermal X-ray emission. Like G347.3-0.5, this low-latitude remnant displays discrete regions of enhanced emission along the rim as well as faint nonthermal emission from the interior. We derive limits on the thermal content of the remnant emission, although the presence of the Vela SNR compromises our ability to seriously constrain a low-temperature component. Limits placed on the amount of Sc-K emission are compared with the expected flux based on the reported 44Ti emission from G266.2-1.2. We also report on an unresolved X-ray source surrounded by diffuse emission near the center of the remnant. The properties of the source are not well determined but appear consistent with the interpretation that the source is a neutron star surrounded by a synchrotron nebula. Alternatively, the source may be associated with one of two stars located within the positional error circle, but this appears somewhat unlikely.

Discovery of a young nearby supernova remnant

About 200 supernova remnants have been found in the galaxy, six of which are younger than about 1,000 years (ref. 2). Observations of these young remnants are important for understanding of the late phases of supernova evolution, and each new object should add substantially to our knowledge of the processes involved. Here I report the discovery of a supernova remnant (RXJ0852.0 − 4622), identified by its X-ray emission, at the southeast corner of the known Vela supernova remnant. The high temperature (>3 × 107 K) indicates an age of less than ∼1,500 yr. The observed diameter of the remnant is about 2°, which suggests a distance of less than 1 kpc, based on a comparison with the remnant of the supernova of AD1006. RXJ0852.0 − 4622 may therefore be the nearest supernova to have occurred during recent human history.

XMM-Newton observation of the brightest X-ray flare detected so far from Sgr A

We report the high S/N observation on October 3, 2002 with XMM-Newton of the brightest X-ray flare detected so far from Sgr A* with a duration shorter than one hour (~2.7 ks). The light curve is almost symmetrical with respect to the peak flare, and no significant difference between the soft and hard X-ray range is detected. The overall flare spectrum is well represented by an absorbed power-law with a soft photon spectral index of

Discovery of Non-Thermal X-Rays from the Northwest Shell of the New SNR RX J1713.7–3946: The Second SN 1006?

\Gamma =2.5 \pm0.3

The Compact Central Object in Cassiopeia A: A Neutron Star with Hot Polar Caps or a Black Hole?

, and a peak 2–10 keV luminosity of 3.6

New light on the X-ray spectrum of the Crab Nebula

^{+0.3}_{-0.4}\times 10 ^{35}

The Cygnus superbubble revisited

erg s -1 , i.e. a factor 160 higher than the Sgr A* quiescent value. No significant spectral change during the flare is observed. This X-ray flare is very different from other bright flares reported so far: it is much brighter and softer. The present accurate determination of the flare characteristics challenge the current interpretation of the physical processes occuring inside the very close environment of Sgr A* by bringing very strong constraints for the theoretical flare models.

The XMM-Newton serendipitous survey: II - First results from the AXIS high galactic latitude medium sensitivity survey

We report ASCA results of a featureless X-ray spectrum from RX J1713.7−3946, a new shell-like SNR discovered with the ROSAT all sky survey. The northwest part of RX J1713.7−3946 was in the field of the ASCA Galactic Plane Survey Project and was found to exhibit a shell-like structure. The spectrum, however shows neither line emission nor any signature of a thermal origin. Instead, a power-law model with a photon index of 2.4-2.5 gives reasonable fit to the spectrum, suggesting a non-thermal origin. Together with the similarity to SN1006, we propose that RX J1713.7−3946 is the second example, after SN1006, of a synchrotron X-ray radiation from a shell of SNRs. Since the synchrotron X-rays suggest existence of extremely high energy charged particles in the SNR shell, our discovery should have strong impact on the origin of the cosmic X-rays.