arXiv subjects

S. D. Van Dyk

Publications and source records attributed to S. D. Van Dyk.

41 records · Page 3Linked to original sources

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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arXiv1999

The Environments of Supernovae in Post-Refurbishment Hubble Space Telescope Images

The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. Access to this information, however, has been hampered by the limited resolution achieved by ground-based observations. High spatial resolution Hubble Space Telescope (HST) images of galaxy fields in which supernovae had been observed can improve the situation considerably. We have examined the immediate environments of a few dozen supernovae using archival post-refurbishment HST images. Although our analysis is limited due to signal-to-noise ratio and filter bandpass considerations, the images allow us for the first time to resolve individual stars in, and to derive detailed color-magnitude diagrams for, several environments. We are able to place more rigorous constraints on the masses of these supernovae. A search was made for late-time emission from supernovae in the archival images, and for the progenitor stars in presupernova images of the host galaxies. We have detected SN 1986J in NGC 891 and, possibly, SN 1981K in NGC 4258. We have also identified the progenitor of the Type IIn SN 1997bs in NGC 3627. By removing younger resolved stars in the environments of SNe Ia, we can measure the colors of the unresolved stellar background and attribute these colors generally to an older, redder population. HST images ``accidentally'' caught the Type Ia SN 1994D in NGC 4526 shortly after its outburst; we measure its brightness. Finally, we add to the statistical inferences that can be made from studying the association of SNe with recent star-forming regions.

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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.

astro-ph↗

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.

astro-ph↗

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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