45 research outputs found
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
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
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
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 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
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
Radio Observations of Supernovae
Study of radio supernovae over the past 25 years includes two dozen detected
objects and more than 100 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 presupernova stellar wind. It
is also possible to detect ionized hydrogen along the line of sight, to
demonstrate binary properties of the stellar system, to detect clumpiness of
the circumstellar material, and to put useful constraints on the progenitors of
undetected Type Ia supernovae.Comment: 8 pages, 4 figures. Invited talk at `The Multicoloured Landscape of
Compact Objects and their Explosive Origins', Cefalu', 2006 June 11-24 (AIP
Conf. Proc.), eds. L. Burderi et al., in pres
Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution
New observations of SN 1980K made with the VLA at 20 and 6 cm from 1994 April
through 1996 October show that the supernova (SN) has undergone a significant
change in its radio emission evolution, dropping by a factor of ~2 below the
flux density S \propto t^{-0.73} power-law decline with time t observed
earlier. However, although S at all observed frequencies has decreased
significantly, its current spectral index of \alpha= -0.42\pm0.15 (S \propto
\nu^{+\alpha}) is consistent with the previous spectral index of
\alpha=-0.60_{-0.07}^{+0.04}.
It is suggested that this decrease in emission may be due to the SN shock
entering a new region of the circumstellar material which has a lower density
than that expected for a constant speed (w), constant mass-loss rate (Mdot)
wind from the progenitor. If such an interpretation is correct, the difference
in wind and shock speeds appears to indicate a significant evolution in the
mass-loss history of the SN progenitor ~10^4 years before explosion, with a
change in circumstellar density (\propto Mdot/w) occurring over a time span of
\lesssim 4 kyr. Such features could be explained in terms of a fast
``blue-loop'' evolutionary phase of a relatively massive pre-SN progenitor
star. If so, we may, for the first time, provide a stringent constraint on the
mass of the SN progenitor based solely on the SN's radio emission.Comment: 22 pages, 3 figures, to appear in Ap
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 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