Matthew T. Kelley

Long-Term Radio Monitoring of SN 1993J

We present our extensive observations of the radio emission from supernova (SN) 1993J, in M81 (NGC 3031), made with the Very Large Array, at 90, 20, 6, 3.6, 2, 1.2, and 0.7 cm, as well as numerous measurements from other telescopes and at other wavelengths. The combined data set constitutes probably the most detailed set of measurements ever established for any SN outside of the Local Group in any wavelength range. The radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well. However, (1) The highest frequency measurements at 85-110 GHz at early times (<40 days) are not well fitted by the parameterization which describes the centimeter wavelength measurements. (2) At midcentimeter wavelengths there is often deviation from the fitted radio light curves. (3) At a time ~3100 days after shock breakout, the decline rate of the radio emission steepens from (t^(+β)) β ~ − 0.7 to –2.7 without change in the spectral index (ν^(+α); α ~ − 0.81); however, this decline is best described not as a power-law, but as an exponential decay with an e-folding time of ~1100 days. (4) The best overall fit to all of the data is a model including both nonthermal synchrotron self-absorption (SSA) and thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate until the break. (5) The radio and X-ray light curves display quite similar behavior and both suggest a sudden increase in the supernova progenitor mass-loss rate occurred at ~8000 yr prior to shock breakout.

ELEVEN YEARS OF RADIO MONITORING OF THE TYPE IIn SUPERNOVA SN 1995N

We present radio observations of the optically bright Type IIn supernova SN 1995N. We observed the SN at radio wavelengths with the Very Large Array for 11 years. We also observed it at low radio frequencies with the Giant Metrewave Radio Telescope at various epochs within 6.5 – 10 years since explosion. Although there are indications of an early optically thick phase, most of the data are in the optically thin regime so it is difficult to distinguish between synchrotron self absorption and free-free absorption (FFA) mechanisms. However, the information from other wavelengths indicates that FFA is the dominant absorption process. Model fits of radio emission with FFA give reasonable physical parameters. Making use of X-ray and optical observations, we derive the physical conditions of the shocked ejecta and the shocked circumstellar matter.

Radio Emission from Supernovae

Study of radio supernovae over the past 27 years includes more than three dozen detected objects and more than 150 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupemova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the presupemova stellar system, and to detect dumpiness of the circumstellar material. Along with reviewing these general properties of the radio emission from supernovae, we present our extensive observations of the radio emission from supemova (SN) 1993J in M 81 (NGC 3031) made with the Very Large Array and other radio telescopes. The SN 1993J radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The highest frequency measurements at 85 - 110 GHz at early times (< 40 days) are not well fitted by the parameterization which describes the cm wavelength measurements rather well. 2) At mid-cm wavelengths there is often deviation from the fitted radio light curves, particularly near the peak flux density, and considerable shorter term deviations in the declining portion when the emission has become optically thin. 3) At a time ~3100 days after shock breakout, the decline rate of the radio emission steepens from (t^(+β))β ~ 0.7 to β ~ —2.7 without change in the spectral index (v^(+α); α ~ -0.81). However, this decline is best described not as a power-law, but as an exponential decay starting at day ~3100 with an e-folding time of ~1100 days. 4) The best overall fit to all of the data is a model including both non-thermal synchrotron self-absorption (SSA) and a thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate, until a break in that decline rate at day ~3100, as mentioned above. Moreover, neither a purely SSA nor a purely FFA absorbing model can provide a fit that simultaneously reproduces the light curves, the spectral index evolution, and the brightness temperature evolution.

Recent Type II Radio Supernovae

We present the results of radio observations, taken primarily with the Very Large Array, of Supernovae 1993J, 2001gd, 2001em, 2002hh, 2004dj, and 2004et. We have fit a parameterized model to the multi‐frequency observations of each supernova. We compare the observed and derived radio properties of these supernovae by optical classification and discuss the implications.

Light Curves of Radio Supernovae

We present the results from the on‐going radio monitoring of recent type II supernovae (SNe), including SNe 2004et, 2004dj, 2002hh, 2001em, and 2001gd. Using the Very Large Array to monitor these supernovae, we present their radio light‐curves. From these data we are able to discuss parameterizations and modeling and make predictions of the nature of the progenitors based on previous research. Derived mass loss rates assume wind‐established circumstellar medium, shock velocity ∼ 10,000 km s−1, wind velocity ∼ 10 km s−1, and CSM Temperature ∼ 10,000 K.