105 research outputs found
The Radio Recovery of SN 1970G: The Continuing Radio Evolution of SN 1970G
Using the Very Large Array, we have detected radio emission from the site of
SN 1970G in the Sc galaxy M101. These observations are 31 years after the
supernova event, making SN 1970G the longest monitored radio supernova. With
flux densities of 0.12 +/- 0.020 mJy at 6 cm and 0.16 +/- 0.015 mJy at 20 cm,
the spectral index of -0.24 +/- 0.20 appears to have flattened somewhat when
compared with the previously reported value of -0.56 +/- 0.11, taken in 1990.
The radio emission at 20 cm has decayed since the 1990 observations with a
power-law index of beta_20cm = -0.28 +/- 0.13. We discuss the radio properties
of this source and compare them to those of other Type II radio supernovae.Comment: 11 pages, 1 table and 2 figures; To appear in Astrophysical Journal
Letter
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
A Radio and X-Ray Study of Historical Supernovae in M83
We report the results of 15 years of radio observations of the six historical
supernovae (SNe) in M83 using the Very Large Array. We note the near linear
decline in radio emission from SN 1957D, a type II SN, which remains a
non-thermal radio emitter. The measured flux densities from SNe 1923A and 1950B
have flattened as they begin to fade below detectable limits, also type II SNe.
The luminosities for these three SNe are comparable with the radio luminosities
of other decades-old SNe at similar epochs. SNe 1945B, 1968L, and 1983N were
not detected in the most recent observations and these non-detections are
consistent with previous studies. We report the X-ray non-detections of all six
historical SNe using the Chandra X-ray Observatory, consistent with previous
X-ray searches of other decades-old SNe, and low inferred mass loss rates of
the progenitors.Comment: 3 color ps figure
Long Term Radio Monitoring of SN 1993J
We present our observations of the radio emission from supernova (SN) 1993J,
in M 81 (NGC 3031), made with the VLA, from 90 to 0.7 cm, as well as numerous
measurements from other telescopes. 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. Only SN 1987A in the LMC has been the
subject of such an intensive observational program. 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-SN stellar
wind describes the observations rather well considering the complexity of the
phenomenon. However: 1) The 85 - 110 GHz measurements at early times are not
well fitted by the parameterization, unlike the cm wavelength measurements. 2)
At mid-cm wavelengths there is some deviation from the fitted radio light
curves. 3) At a time ~3100 days after shock breakout, the decline rate of the
radio emission steepens without change in the spectral index. This decline is
best described 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 the break in that decline
rate. Moreover, neither a purely SSA nor a purely FFA absorbing models can
provide a fit that simultaneously reproduces the light curves, the spectral
index evolution, and the brightness temperature evolution. 5) The radio and
X-ray light curves exhibit similar behavior and suggest a sudden drop in the SN
progenitor mass-loss rate at ~8000 years prior to shock breakout.Comment: 45 pages, 13 figures, accepted for Ap
The Fading Radio Emission from SN 1961V: Evidence for a Type II Peculiar Supernova?
Using the Very Large Array (VLA), we have detected radio emission from the
site of SN 1961V in the Sc galaxy NGC 1058. With a peak flux density of 0.063
+/- 0.008 mJy/beam at 6 cm and 0.147 +/- 0.026 mJy/beam at 18 cm, the source is
non-thermal, with a spectral index of -0.79 +/- 0.23. Within errors, this
spectral index is the same value reported for previous VLA observations taken
in 1984 and 1986. The radio emission at both wavelengths has decayed since the
mid 1980's observations with power-law indices of beta(20cm) = -0.69 +/- 0.23
and beta(6cm) = -1.75 +/- 0.16. We discuss the radio properties of this source
and compare them with those of Type II radio supernovae and luminous blue
variables.Comment: 19 pages, 3 figures; To appear in the Astronomical Journa
Recovery of the Historical SN1957D in X-rays with Chandra
SN1957D, located in one of the spiral arms of M83, is one of the small number
of extragalactic supernovae that has remained detectable at radio and optical
wavelengths during the decades after its explosion. Here we report the first
detection of SN1957D in X-rays, as part of a 729 ks observation of M83 with
\chandra. The X-ray luminosity (0.3 - 8 keV) is 1.7 (+2.4,-0.3) 10**37 ergs/s.
The spectrum is hard and highly self-absorbed compared to most sources in M83
and to other young supernova remnants, suggesting that the system is dominated
at X-ray wavelengths by an energetic pulsar and its pulsar wind nebula. The
high column density may be due to absorption within the SN ejecta. HST WFC3
images resolve the supernova remnant from the surrounding emission and the
local star field. Photometry of stars around SN1957D, using WFC3 images,
indicates an age of less than 10**7 years and a main sequence turnoff mass more
than 17 solar masses. New spectra obtained with Gemini-South show that the
optical spectrum continues to be dominated by broad [O III] emission lines, the
signature of fast-moving SN ejecta. The width of the broad lines has remained
about 2700 km/s (FWHM). The [O III] flux dropped precipitously between 1989 and
1991, but continued monitoring shows the flux has been almost constant since.
In contrast, radio observations over the period 1990-2011 show a decline rate
inf the flux proportional to t**-4, far steeper than the rate observed earlier,
suggesting that the primary shock has overrun the edge of a pre-SN wind.Comment: 28 pages, including 3 tables and 7 figures, accepted for publication
in Ap
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
The Nature of SN 1961V
The nature of SN 1961V has been uncertain. Its peculiar optical light curve
and slow expansion velocity are similar to those of super-outbursts of luminous
blue variables (LBVs), but its nonthermal radio spectral index and declining
radio luminosity are consistent with decades-old supernovae (SNe). We have
obtained Hubble Space Telescope STIS images and spectra of the stars in the
vicinity of SN 1961V, and find Object 7 identified by Filippenko et al. to be
the closest to the optical and radio positions of SN 1961V. Object 7 is the
only point source detected in our STIS spectra and only its H-alpha emission is
detected; it cannot be the SN or its remnant because of the absence of
forbidden lines. While the H-alpha line profile of Object 7 is remarkably
similar to that of eta Car, the blue color (similar to an A2Ib supergiant) and
lack of appreciable variability are unlike known post-outburst LBVs. We have
also obtained Very Long Baseline Array (VLBA) observations of SN 1961V at 18
cm. The non-detection of SN 1961V places a lower limit on the size of the
radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion
velocity in excess of 4,400 km/s, much higher than the optical expansion
velocity measured in 1961. We conclude the following: (1) A SN occurred in the
vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum
originates from a giant eruption of a massive star, Object 7 is the most
probable candidate for the survivor, but its blue color and lack of significant
variability are different from a post-outburst eta Car. (3) The radio SN and
Object 7 could be physically associated with each other through a binary
system. (4) Object 7 needs to be monitored to determine its nature and
relationship to SN 1961V.Comment: 16 pages, 3 figures, accepted by the Astronomical Journal for the
2004 May issu
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
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