SN 1996cr: Confirmation of a Luminous Type IIn Supernova in the Circinus Galaxy

We have recently confirmed SN 1996cr as a late-time type IIn supernova (SN) via VLT spectroscopy and isolated its explosion date to ~1 yr using archival optical imaging. We briefly touch upon here the wealth of optical, X-ray, and radio archival observations available for this enigmatic source. Due to its relative proximity (3.8 +/-0.6 Mpc), SN 1996cr ranks among the brightest X-ray and radio SNe ever detected and, as such, may offer powerful insights into the structure and composition of type IIn SNe. We also find that SN 1996cr is matched to GRB 4B 960202 at a 2-3 sigma confidence level, making it perhaps the third GRB to be significantly associated with a type II SN. We speculate on whether SN 1996cr could be an off-axis or ``failed'' GRB.Comment: 3 pages, 1 figure, poster proceeding for "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra

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.Comment: 14 pages, LaTeX (AASTeX), 2 PostScript figures, to appear in ApJ (Letters

SN1998bw/GRB980425 and Radio Supernovae

The unusual supernova SN1998bw, which is thought to be related to the gamma-ray burster GRB980425, is a possible link between the two classes of objects. Analyzing the extensive radio emission data avaliable for SN1998bw, we are able to describe its time evolution within the well established framework available for the analysis of radio emission from supernovae. This then allows description of a number of physical properties of the object. The radio emission can best be explained as interaction of a mildly relativistic (Gamma about 1.6) shock with a dense pre-explosion stellar wind established circumstellar medium (CSM) which is highly structured both azimuthally, in clumps or filaments, and radially, with two observed density enhancements separated by about 3e17 cm. With assumptions as to pre-explosion stellar wind conditions, it is possible to estimate that the progenitor to SN 1998bw had a mass loss rate of about 3.5e-5 solar masses per yr with at least two approximately 30% increases in mass-loss rate; the most recent extending from about 1,600 - 4,700 yr before explosion and the oldest known having occurred, with possibly comparable length, about 12,000 yr before explosion. Because of its unusual characteristics for a Type Ib/c SN, the relation of SN1998bw to GRB980425 is strengthened with consequent improvement in our understanding of these poorly understood objects.Comment: 24 pages, 2 figures, to appear in Astrophysical Journa

Radio emission from SNe and young SNRs

Study of radio supernovae (RSNe), the earliest stages of supernova remnant (SNR) formation, over the past 20 years includes two dozen detected objects and more than 100 upper limits. From this work we are able 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 presupernova 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 stellar system, and to show clumpiness of the circumstellar material. More speculatively, it may be possible to provide distance estimates to RSNe

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.Comment: 5 pages, 2 figures, 1 table Conference Proceedings: "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters" AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCra

Swift UVOT Observations of Core-Collapse SNe

We review recent UV observations of core-collapse supernovae (SNe) with the Swift Ultra-violet/Optical Telescope (UVOT) during its first two years. Rest-frame UV photometry is useful for differentiating SN types by exploiting the UV-optical spectral shape and more subtle UV features. This is useful for the real-time classification of local and high-redshift SNe using only photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV observations are also useful for constraining the temperature and ionization structure of SNe IIP. Rest-frame UV observations of all types are important for understanding the extinction, temperature, and bolometric luminosity of SNe and to interpret the observations of high redshift SNe observed at optical wavelengths.Comment: Figures are enlarged and colorized from print versio

The Radio Evolution of SN 2001gd

We present the results of observations of the radio emission from Supernova 2001gd in NGC 5033 from 2002 February 8 through 2006 September 25. The data were obtained using the Very Large Array at wavelengths of 1.3 cm (22.4 GHz), 2 cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by the Giant Metrewave Radio Telescope at 21 cm (1.4 GHz). SN 2001gd was discovered in the optical well past maximum light, so that it was not possible to obtain many of the early radio "turn-on" measurements which are important for estimating the local circumstellar medium (CSM) properties. Only at 20 cm were turn-on data available. However, our analysis and fitting of the radio light curves, and the assumption that the Type IIb SN 2001gd resembles the much better studied Type IIb SN 1993J, enables us to describe the radio evolution as being very regular through day ~550 and consistent with a nonthermal-emitting model with a thermal absorbing CSM. The presence of synchrotron-self absorption (SSA) at early times is implied by the data, but determination of the exact relationship between the SSA component from the emitting region and the free-free absorption component from the CSM is not possible as there are insufficient early measurements to distinguish between models. After day ~550, the radio emission exhibits a dramatically steeper decline rate which, assuming similarity to SN 1993J, can be described as an exponential decrease with an e-folding time of 500 days. We interpret this abrupt change in the radio flux density decline rate as implying a transition of the shock front into a more tenuous region of circumstellar material. A similar change in radio evolution has been seen earlier in other SNe such as SN 1988Z, SN 1980K, and SN 1993J.Comment: 3 tables, 2 figures, To appear in the Astrophysical Journa

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 (VLA) for 11 years. We also observed it at low radio frequencies with the Giant Metrewave Radio Telescope (GMRT) 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 (SSA) and free-free absorption (FFA) mechanisms. However, the information from other wavelengths indicates that the FFA is the dominant absorption process. Model fits of radio emission with the 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 CSM.Comment: 22 pages, 2 tables, 13 figures, Accepted for publication in Astrophysical Journa

Radio Emission from SN 2001gd in NGC 5033

We present the results of monitoring the radio emission from the Type IIb supernova SN 2001gd between 2002 February 8 and 2002 October 28. Most of the data were obtained using the Very Large Array at the five wavelengths of $\lambda \lambda$1.3 cm (22.4 GHz), 2.0 cm (14.9 GHz), 3.6 cm (8.44 GHz), 6.2 cm (4.86 GHz), and 21 cm (1.4 GHz). Observations were also made with Giant Meterwave Radio Telescope at $\lambda$21 cm (1.4 GHz). The object was discovered optically well after maximum light, making any determination of the early radio evolution difficult. However, subsequent observations indicate that the radio emission has evolved regularly in both time and frequency and is well described by the SN shock/circumstellar medium interaction model.Comment: 16 pages 2 figures to appear in Astrophysical Journa