643 research outputs found
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
Short-period line profile and light variations in the Beta Cephei star 19 Monocerotis
We present an analysis of 555 high-dispersion echelle spectra of 19 Mon obtained from two sites as well as 115 Strömgren uvby observations. We show that three periodicities are present at 5.229 94, 0.170 19 and 4.889 56 cycle d−1. The first periodicity has by far the largest amplitude. Photometric amplitude ratios and phase differences indicate an ℓ=2 mode, while the line profile variations unequivocally point to ℓ=2,m=-2. Because of the low amplitudes of the other two modes, very little can be said concerning them. Although 19 Mon was originally selected on the basis of its classification as a marginal Be star, the Be nature of the star is not supported by our observation
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
Incorporating Uncertainties in Atomic Data Into the Analysis of Solar and Stellar Observations: A Case Study in Fe XIII
Information about the physical properties of astrophysical objects cannot be
measured directly but is inferred by interpreting spectroscopic observations in
the context of atomic physics calculations. Ratios of emission lines, for
example, can be used to infer the electron density of the emitting plasma.
Similarly, the relative intensities of emission lines formed over a wide range
of temperatures yield information on the temperature structure. A critical
component of this analysis is understanding how uncertainties in the underlying
atomic physics propagates to the uncertainties in the inferred plasma
parameters. At present, however, atomic physics databases do not include
uncertainties on the atomic parameters and there is no established methodology
for using them even if they did. In this paper we develop simple models for the
uncertainties in the collision strengths and decay rates for Fe XIII and apply
them to the interpretation of density sensitive lines observed with the EUV
Imagining spectrometer (EIS) on Hinode. We incorporate these uncertainties in a
Bayesian framework. We consider both a pragmatic Bayesian method where the
atomic physics information is unaffected by the observed data, and a fully
Bayesian method where the data can be used to probe the physics. The former
generally increases the uncertainty in the inferred density by about a factor
of 5 compared with models that incorporate only statistical uncertainties. The
latter reduces the uncertainties on the inferred densities, but identifies
areas of possible systematic problems with either the atomic physics or the
observed intensities.Comment: in press at Ap
The Jacobian as a measure of planar dose congruence
We propose a new starting point for comparing dose distributions in
therapeutic radiation physics using a Jacobian-based measure. The measure is
normalization independent, free of tunable parameters, bounded and converges to
a unique value when comparing unrelated dose distributions. We present a
preliminary demonstration of the sensitivity and general characteristics of
this measure.Comment: 9 pages, 2 figure
Core-Collapse Supernovae and Host Galaxy Stellar Populations
We have used images and spectra of the Sloan Digital Sky Survey to examine
the host galaxies of 519 nearby supernovae. The colors at the sites of the
explosions, as well as chemical abundances, and specific star formation rates
of the host galaxies provide circumstantial evidence on the origin of each
supernova type. We examine separately SN II, SN IIn, SN IIb, SN Ib, SN Ic, and
SN Ic with broad lines (SN Ic-BL). For host galaxies that have multiple
spectroscopic fibers, we select the fiber with host radial offset most similar
to that of the SN. Type Ic SN explode at small host offsets, and their hosts
have exceptionally strongly star-forming, metal-rich, and dusty stellar
populations near their centers. The SN Ic-BL and SN IIb explode in
exceptionally blue locations, and, in our sample, we find that the host spectra
for SN Ic-BL show lower average oxygen abundances than those for SN Ic. SN IIb
host fiber spectra are also more metal-poor than those for SN Ib, although a
significant difference exists for only one of two strong-line diagnostics. SN
Ic-BL host galaxy emission lines show strong central specific star formation
rates. In contrast, we find no strong evidence for different environments for
SN IIn compared to the sites of SN II. Because our supernova sample is
constructed from a variety of sources, there is always a risk that sampling
methods can produce misleading results. We have separated the supernovae
discovered by targeted surveys from those discovered by galaxy-impartial
searches to examine these questions and show that our results do not depend
sensitively on the discovery technique.Comment: Accepted by the Astrophysical Journal (22 July 2012), conclusions not
changed, extended discussion of sample construction and updated SN
spectroscopic type
Simultaneous XMM-Newton and ESO VLT observations of SN 1995N: probing the wind/ejecta interaction
We present the results of the first {\it XMM-Newton} observation of the
interacting type IIn supernova 1995N, performed in July 2003. We find that the
0.2--10.0 keV unabsorbed flux dropped at a value of erg cm s, almost one order of magnitude lower than that
of a previous {\it ASCA} observation of January 1998. From all the available
X-ray measurements, an interesting scenario emerges where the X-ray light
emission may be produced by a two-phase (clumpy/smooth) circumstellar medium.
The X-ray spectral analysis shows statistically significant evidence for the
presence of two distinct components, that can be modeled with emission from
optically thin, thermal plasmas at different temperatures. The exponent of the
ejecta density distribution inferred from these temperatures is .
From the fluxes of the two spectral components we derive an estimate of the
mass loss rate of the supernova progenitor, , at the upper end of the interval exhibited by red
super-giants. Coordinated optical and infrared observations allow us to
reconstruct the simultaneous infrared to X-ray flux distribution of SN 1995N.
We find that, at 9 years after explosion, the direct X-ray thermal
emission due to the wind/ejecta interaction is times larger than the
total reprocessed IR/optical flux.Comment: 11 pages, 7 figures, MNRAS, in pres
A Spitzer Space Telescope Study of SN 2002hh: An Infrared Echo from a Type IIP Supernova
We present late-time (590-994 days) mid-IR photometry of the normal but highly reddened Type IIP supernova SN 2002hh. Bright, cool, slowly fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star formation region or molecular cloud along the line of sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly condensed dust and/or an ejecta/CSM impact, but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M☉ with a corresponding CSM mass of 3.6(0.01/rdg) M☉, where rdg is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content
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