arXiv subjects

B. Aschenbach

Publications and source records attributed to B. Aschenbach.

41 records · Page 3Linked to original sources

arXiv1998

Temporal Variability of the X-ray Emission of the Crab Nebula Torus

We have analyzed five ROSAT HRI images of the Crab Nebula spanning the years 1991 to 1997 and have found significant changes in the emission structure of the X-ray torus surrounding the pulsar. Certain regions increase in brightness by about 20% over the six years, while others show decreases in surface brightness. The origin of these changes is unclear, but a possible explanation is that the bulk velocity of the synchrotron radiating electrons has decreased on the order of 20% as well.

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arXiv1997

The ROSAT-HRI X-Ray Survey of the Cygnus Loop

We describe and report progress on the joint U.S. and German campaign to map the X-ray emission from the entire Cygnus Loop supernova remnant with the ROSAT High Resolution Imager. The Cygnus Loop is the prototype for a supernova remnant that is dominated by interactions with the interstellar medium and supplies fundamental physical information on this basic mechanism for shaping the interstellar medium. The global view that these high-resolution observations provide emphasizes the inhomogeneity of the interstellar medium and the pivotal nature of cloud-blast wave interactions in determining the X-ray morphology of the supernova remnant. While investigating the details of the evolution of the blast wave, we also describe the interstellar medium in the vicinity of the Cygnus Loop, which the progenitor star has processed. Although we do not expect the X-ray observations to be complete until September 1997, the incomplete data combined with deep H$α$ images provide definitive evidence that the Cygnus Loop was formed by an explosion within a preexisting cavity.

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arXiv1996

The X-ray lightcurve of SN 1987A

X-ray observations of SN 1987A in the Magellanic Clouds have been performed throughout the ROSAT mission, using the PSPC and the HRI detectors. We present the X-ray light curve based on all observations in the years 1991-1995. For the first time a significant increase of the X-ray flux from SN 1987A can be seen, corresponding to X-ray luminosities (0.5-2 keV) of 0.8 - 2.2 X 10**34 erg/s about 4 - 8 years after the explosion. SN 1987A is surrounded by a ringlike nebula, which is thought to form the interface between the blue-supergiant wind and the denser red-supergiant wind of the progenitor. The X-ray data can constrain the density of the matter inside the ring to about 30 amu/cm**3 and the date at which the blast wave will reach the ring to about AD 2003, when a dramatic brightening is expected to occur. Nevertheless, other interpretations of the X-ray emission are possible.

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arXiv1995

ROSAT HRI Observations of the Crab Pulsar: An Improved Temperature upper limit for PSR 0531+21

ROSAT HRI observations have been used to determine an upper limit of the Crab pulsar surface temperature from the off-pulse count rate. For a neutron star mass of 1.4 \Mo and a radius of 10 km as well as the standard distance and interstellar column density, the redshifted temperature upper limit is\/ $T_s^\infty \le 1.55\times 10^6$ K $(3σ)$. This is the lowest temperature upper limit obtained for the Crab pulsar so far. Slightly different values for $T_s^\infty$ are computed for the various neutron star models available in the literature, reflecting the difference in the equation of state.

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arXiv1994

G272.2--3.2: A centrally filled and possibly young SNR discovered by ROSAT

We report the discovery of a new SNR in the \ros All-Sky-Survey data. The SNR has a nearly circular shape with a diameter of about 15 arcmin. The surface brightness is rather uniform over the remnant. The observed interstellar absorption suggests a distance of about 1.8$^{+1.4}_{-0.8}$ kpc. The X-ray emission appears to be of thermal origin with a plasma temperature of about 10$^7$ K. The Sedov model leads to an age of only 1800 years. We find no spectral evidence of non-thermal emission in the center of the remnant. The two most likely explanations for the centrally filled structure are evaporation of shock heated clouds in the interior of the remnant or a reverse shock heating the ejecta of the SNR explosion.

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