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15 results on '"Kahabka, Peter"'

1. Discovery of an Optical Counterpart to the Supersoft X-ray Source in the Globular Cluster M3

Author

Edmonds, Peter D., Kahabka, Peter, and Heinke, Craig O.

Subjects
Astrophysics
Abstract

We report the detection, with HST, of an optical counterpart to the transient supersoft X-ray source 1E 1339.8+2837, in the globular cluster M3. The counterpart is found near the faint end of the subgiant branch in the V vs V-I color magnitude diagram, but is extremely bright in U. Variability is detected over a range of timescales suggesting the presence of an accretion disk and perhaps also ellipsoidal variations of the subgiant secondary. The optical colors of the binary are similar to those of cataclysmic variables recently discovered in 47 Tucanae and NGC 6397. We suggest that magnetically channeled accretion may explain the relatively low X-ray luminosity of this source's supersoft state., Comment: 11 pages, 3 figures, 2 tables. Accepted for publication in ApJ

Published
2004
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2. The M31 population of supersoft sources

Author

Kahabka, Peter

Subjects
Astrophysics
Abstract

The 1991 ROSAT PSPC M31 X-ray point source catalog has been screened in order to set up a sample of candidate supersoft sources in this galaxy, additional to the 16 supersoft sources of Supper et al. (1997). 26 candidates have been found. Absorbing hydrogen column densities, effective temperatures and white dwarf masses (assuming the sources are on the stability line of surface nuclear burning) are derived. An observed white dwarf mass distribution is derived which indicates that the masses are constrained to values above 0.90 solar masses. The entire population of supersoft sources in M31 is estimated taking a theoretical white dwarf mass distribution into account, assuming that the observationally derived sample is restricted to white dwarf masses above 0.90 solar, and taking into account that the gas and the source population have a different scale height. A total number of at least 200-500 and at most 6,000-15,000 sources is deduced depending on the used galaxy N_H model, making use of the population synthesis calculation of Yungelson (1996). The spatial distribution favors a disk (or spiral-arm) dominated young stellar population with a ratio of 1/(4-7) of bulge/disk systems. Assuming that all supersoft sources with masses in excess of 0.5 solar masses are progenitors of supernovae of type Ia, a SN Ia rate of (0.8-7) 10^-3 yr^-1 is derived for M31 based on these progenitors. Supersoft sources might account for 20-100% of the total SN Ia rate in a galaxy like M31., Comment: 13 pages, accepted by A&A January 11th 1999

Published
1999

3. ROSAT observations of the magellanic clouds

Author

Pietsch, Wolfgang, Kahabka, Peter, Araki, H., editor, Brézin, E., editor, Ehlers, J., editor, Frisch, U., editor, Hepp, K., editor, Jaffe, R.L., editor, Kippenhahn, R., editor, Weidenmüller, H.A., editor, Wess, J., editor, Zittartz, J., editor, Beiglböck, W., editor, Baschek, Bodo, editor, Klare, Gerhard, editor, and Lequeux, James, editor

Published
1993
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6. ROSAT survey view of the SMC

Author

Kahabka, Peter, Pietsch, Wolfgang, Araki, H., editor, Brézin, E., editor, Ehlers, J., editor, Frisch, U., editor, Hepp, K., editor, Jaffe, R.L., editor, Kippenhahn, R., editor, Weidenmüller, H.A., editor, Wess, J., editor, Zittartz, J., editor, Beiglböck, W., editor, Baschek, Bodo, editor, Klare, Gerhard, editor, and Lequeux, James, editor

Published
1993
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15. Supersoft X-ray Stars.

Author

Kahabka, Peter, van den Heuvel, Edward P. J., and Rappaport, Saul A.

Subjects
*WHITE dwarf stars, *X-ray astronomy, *SUPERNOVAE, *NUCLEAR fusion, *GAMMA rays, *SUPERMASSIVE black holes, *NEUTRON stars
Abstract

The article discusses white dwarf stars and supersoft sources of low energy x-rays. Since the 1930s astronomers have known that ordinary stars shine because of nuclear fusion deep in their interior. Recently, however, researchers have discovered a new class of stars in which the nuclear fusion takes place not in the deep interior but in the outer layers just below the surface. These stars appear to be white dwarfs--dense, burned out stars that have exhausted their nuclear fuel-in orbit around ordinary stars. The dwarfs steal hydrogen gas from their companions, accumulate it on their surface and resume fusion. The result is a torrent of x-rays with a distinctive "soft" range of wavelengths; such stars are known as luminous supersoft x-ray sources As the dwarfs gain weight, they eventually grow unstable, at which point they can collapse into an even denser neutron star or explode. The disruption of white dwarfs has long been considered as the cause of one sort of supernova explosion, called type 1a. With the discovery of the supersoft sources, observers have identified for the first time a class of star system that can detonate in its way. Type 1a supernovae have become important as bright "standard candles" for measuring distances to faraway galaxies and thereby the pace of cosmic expansion. Much of the lingering uncertainty in estimates of the age and the expansion rate of the universe is connected to astronomers' ignorance of what gives rise to these supernovae. Supersoft sources may be one of the long-sought missing links. Some theoretical physicists suggested that the supersoft sources were white dwarfs that gave off x-rays as gas crashed onto their surface--much as hard x-ray sources result from the accretion of matter onto a neutron star or into a black hole.

Published
2004

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