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Date and Time of the Query: 2019-08-18 T02:00:56 PDT
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For refcode 2002ApJ...572..932P:
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2002ApJ...572..932P X-Ray, Optical, and Radio Observations of the Type II Supernovae 1999em and 1998S David Pooley, Walter H. G. Lewin, Derek W. Fox, Jon M. Miller, Christina K. Lacey, Schuyler D. Van Dyk, Kurt W. Weiler, Richard A. Sramek, Alexei V. Filippenko, Douglas C. Leonard, Stefan Immler, Roger A. Chevalier, Andrew C. Fabian, Claes Fransson, and Ken'ichi Nomoto Received 2001 September 4; accepted 2002 February 2 ABSTRACT Observations of the Type II-P (plateau) supernova SN 1999em and Type IIn (narrow emission line) SN 1998S have enabled estimation of the profile of the SN ejecta, the structure of the circumstellar medium (CSM) established by the pre-SN stellar wind, and the nature of the shock interaction. SN 1999em is the first Type II-P detected at both X-ray and radio wavelengths. It is the least radio luminous and one of the least X-ray luminous SNe ever detected (except for the unusual and very close SN 1987A). The Chandra X-ray data indicate nonradiative interaction of SN ejecta with a power-law density profile ({rho} is proportional to r^-n^, with n ~ 7) for a pre-SN wind with a low mass-loss rate of ~2 x 10^-6^ M_sun_ yr^-1^ for a wind velocity of 10 km s^-1^, in agreement with radio mass-loss rate estimates. The Chandra data show an unexpected, temporary rise in the 0.4-2.0 keV X-ray flux at ~100 days after explosion. SN 1998S, at an age of more than 3 yr, is still bright in X-rays and is increasing in flux density at centimeter radio wavelengths. Spectral fits to the Chandra data show that many heavy elements (Ne, Al, Si, S, Ar, and Fe) are overabundant with respect to solar values. We compare the observed elemental abundances and abundance ratios to theoretical calculations and find that our data are consistent with a progenitor mass of approximately 15-20 M_sun_ if the heavy-element ejecta are radially mixed out to a high velocity. If the X-ray emission is from the reverse shock wave region, the supernova density profile must be moderately flat at a velocity ~10^4^ km s^-1^, the shock front is nonradiative at the time of the observations, and the mass-loss rate is (1-2) x 10^-4^ M_sun_ yr^-1^ for a presupernova wind velocity of 10 km s^-1^. This result is also supported by modeling of the radio emission, which implies that SN 1998S is surrounded by a clumpy or filamentary CSM established by a high mass-loss rate, ~2 x 10^-4^ M_sun_ yr^-1^, from the presupernova star. Subject headings: radio continuum: ISM - stars: mass loss - supernovae: individual (SN 1998S, SN 1999em) - X-rays: individual (SN 1998S, SN 1999em) - X-rays: ISM
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