2,206 research outputs found
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 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
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
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