arXiv subjects

K. W. Weiler

Publications and source records attributed to K. W. Weiler.

24 records · Page 2Linked to original sources

arXiv2002

Strongly decelerated expansion of SN1979C

We observed SN1979C in M100 on 4 June 1999, about twenty years after explosion, with a very sensitive four-antenna VLBI array at the wavelength of 18cm. The distance to M100 and the expansion velocities are such that the supernova cannot be fully resolved by our Earth-wide array. Model-dependent sizes for the source have been determined and compared with previous results. We conclude that the supernova shock was initially in free expansion for 6 +/- 2 yrs and then experienced a very strong deceleration. The onset of deceleration took place a few years before the abrupt trend change in the integrated radio flux density curves. We estimate the shocked swept-up mass to be about 1.6 solar masses, assuming a standard density profile for the CSM. Such a swept-up mass for SN1979C suggests a mass of the hydrogen-rich envelope ejected at explosion no larger than $M_{\rm env} \sim$ 0.9 solar masses. If SN1979C originated in a binary star the low value of M_env suggests that the companion of the progenitor star stripped off most of the hydrogen-rich envelope mass of the presupernova star prior to the explosion.

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arXiv2001

Radio Spectral Index and Expansion of 3C58

We present new observations of the plerionic supernova remnant 3C58 with the VLA at 74 and 327 MHz. In addition, we re-reduced earlier observations at 1.4 and 4.9 GHz taken in 1973 and 1984. Comparing these various images, we find that: 1. the remnant has a flat and relatively uniform spectral index distribution, 2. any expansion of the remnant with time is significantly less than that expected for uniform, undecelerated expansion since the generally accepted explosion date in 1181 A.D., and 3. there is no evidence for a non-thermal synchrotron emission shell generated by a supernova shock wave, with any such emission having a surface brightness of <1 x 10^(-21) W / (m^2 Hz sr) at 327 MHz.

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arXiv1999

Radio Supernovae and the Square Kilometer Array

Detailed radio observations of extragalactic supernovae are critical to obtaining valuable information about the nature and evolutionary phase of the progenitor star in the period of a few hundred to several tens-of-thousands of years before explosion. Additionally, radio observations of old supernovae (>20 years) provide important clues to the evolution of supernovae into supernova remnants, a gap of almost 300 years (SN ~1680=Cas A, to SN 1923A) in our current knowledge. Finally, new empirical relations indicate that it may be possible to use some types of radio supernovae as distance yardsticks, to give an independent measure of the distance scale of the Universe. However, the study of radio supernovae is limited by the sensitivity and resolution of current radio telescope arrays. Therefore, it is necessary to have more sensitive arrays, such as the Square Kilometer Array and the several other radio telescope upgrade proposals, to advance radio supernova studies and our understanding of supernovae, their progenitors, and the connection to supernova remnants.

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arXiv1998

Radio Supernovae as Distance Indicators

Long-term monitoring of the radio emission from supernovae with the Very Large Array (VLA) shows that the radio ``light curves'' evolve in a systematic fashion with a distinct peak flux density (and thus, in combination with a distance, a peak spectral luminosity) at each frequency and a well-defined time from explosion to that peak. Studying these two quantities at 6 cm wavelength, peak spectral luminosity (L_{6 cm peak}) and time after explosion date (t_0) to reach that peak (t_{6 cm peak} - t_0), we find that they appear related. In particular, based on two objects, Type Ib supernovae may be approximate radio ``standard candles'' with a 6 cm peak luminosity L_{6 cm peak} \approx 19.9 X 10^{26} erg s^{-1} Hz^{-1}; also based on two objects, Type Ic supernovae may be approximate radio ``standard candles'' with a 6 cm peak luminosity L_{6 cm peak} \approx 6.5 X 10^{26} erg s^{-1} Hz^{-1}; and, based on twelve objects, Type II supernovae appear to obey a relation L_{6 cm peak} \simeq 5.5 X 10^{23} (t_{6 cm peak} - t_0)^{1.4} erg s^{-1} Hz^{-1}, with time measured in days. If these relations are supported by further observations, they provide a means for determining distances to supernovae, and thus to their parent galaxies, from purely radio continuum observations.

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arXiv1997

Deceleration in the Expansion of SN1993J

A rarity among supernova, SN 1993J in M81 can be studied with high spatial resolution. Its radio power and distance permit VLBI observations to monitor the expansion of its angular structure. This radio structure was previously revealed to be shell-like and to be undergoing a self-similar expansion at a constant rate. From VLBI observations at the wavelengths of 3.6 and 6 cm in the period 6 to 42 months after explosion, we have discovered that the expansion is decelerating. Our measurement of this deceleration yields estimates of the density profiles of the supernova ejecta and circumstellar material in standard supernova explosion models.

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arXiv1997

Radio Detection of SN 1986E in NGC 4302

Radio observations of SN 1986E have shown a clear detection of emission at 6 cm wavelength about 8 months after optical discovery. Combined with a number of new upper limits and a study of the possible models, it appears that SN 1986E was probably a fairly normal Type IIL supernova, somewhat similar to SN 1980K, with radio emission at roughly expected levels. This detection continues the correlation between radio detection and late time optical emission.

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