899 research outputs found
Determining the Type, Redshift, and Phase of a Supernova Spectrum
We present an algorithm to identify the types of supernova spectra, and
determine their redshift and phase. This algorithm, based on the correlation
techniques of Tonry & Davis, is implemented in the SuperNova IDentification
code (SNID). It is used by members of the ESSENCE project to determine whether
a noisy spectrum of a high-redshift supernova is indeed of type Ia, as opposed
to, e.g., type Ib/c. Furthermore, by comparing the correlation redshifts
obtained using SNID with those determined from narrow lines in the supernova
host galaxy spectrum, we show that accurate redshifts (with a typical error <
0.01) can be determined for SNe Ia for which a spectrum of the host galaxy is
unavailable. Last, the phase of an input spectrum is determined with a typical
accuracy of ~3 days.Comment: 10 pages, 7 figures. To appear in "The Multicoloured Landscape of
Compact Objects and their Explosive Progenitors: Theory vs Observations"
(Cefalu, Sicily, June 2006). Eds. L. Burderi et al. (New York: AIP
Supernova cosmology: legacy and future
The discovery of dark energy by the first generation of high-redshift
supernova surveys has generated enormous interest beyond cosmology and has
dramatic implications for fundamental physics. Distance measurements using
supernova explosions are the most direct probes of the expansion history of the
Universe, making them extremely useful tools to study the cosmic fabric and the
properties of gravity at the largest scales. The past decade has seen the
confirmation of the original results. Type Ia supernovae are among the leading
techniques to obtain high-precision measurements of the dark energy equation of
state parameter, and in the near future, its time dependence. The success of
these efforts depends on our ability to understand a large number of effects,
mostly of astrophysical nature, influencing the observed flux at Earth. The
frontier now lies in understanding if the observed phenomenon is due to vacuum
energy, albeit its unnatural density, or some exotic new physics. Future
surveys will address the systematic effects with improved calibration
procedures and provide thousands of supernovae for detailed studies.Comment: Invited review, Annual Review of Nuclear and Particle Science
(submitted version
Spherically symmetric relativistic MHD simulations of pulsar wind nebulae in supernova remnants
Pulsars, formed during supernova explosions, are known to be sources of
relativistic magnetized winds whose interaction with the expanding supernova
remnants (SNRs) gives rise to a pulsar wind nebula (PWN). We present
spherically symmetric relativistic magnetohydrodynamics (RMHD) simulations of
the interaction of a pulsar wind with the surrounding SNR, both in particle and
magnetically dominated regimes. As shown by previous simulations, the evolution
can be divided in three phases: free expansion, a transient phase characterized
by the compression and reverberation of the reverse shock, and a final Sedov
expansion. The evolution of the contact discontinuity between the PWN and the
SNR (and consequently of the SNR itself) is almost independent of the
magnetization of the nebula as long as the total (magnetic plus particle)
energy is the same. However, a different behaviour of the PWN internal
structure is observable during the compression-reverberation phase, depending
on the degree of magnetization=2E The simulations were performed using the
third order conservative scheme by Del Zanna et al. (2003).Comment: 11 pages, Latex, 22 Encapsulated PostScript figures, accepted f or
publication on A&
The effects of spin-down on the structure and evolution of pulsar wind nebulae
We present high resolution spherically symmetric relativistic
magnetohydrodynamical simulations of the evolution of a pulsar wind nebula
inside the free expanding ejecta of the supernova progenitor. The evolution is
followed starting from a few years after the supernova explosion and up to an
age of the remnant of 1500 years. We consider different values of the pulsar
wind magnetization parameter and also different braking indices for the
spin-down process. We compare the numerical results with those derived through
an approximate semi-analytical approach that allows us to trace the time
evolution of the positions of both the pulsar wind termination shock and the
contact discontinuity between the nebula and the supernova ejecta. We also
discuss, whenever a comparison is possible, to what extent our numerical
results agree with former self-similar models, and how these models could be
adapted to take into account the temporal evolution of the system. The inferred
magnetization of the pulsar wind could be an order of magnitude lower than that
derived from time independent analytic models.Comment: 11 pages, 7 figures, Accepted for publication on A&
On the Interpretation of Supernova Light Echo Profiles and Spectra
The light echo systems of historical supernovae in the Milky Way and local
group galaxies provide an unprecedented opportunity to reveal the effects of
asymmetry on observables, particularly optical spectra. Scattering dust at
different locations on the light echo ellipsoid witnesses the supernova from
different perspectives and the light consequently scattered towards Earth
preserves the shape of line profile variations introduced by asymmetries in the
supernova photosphere. However, the interpretation of supernova light echo
spectra to date has not involved a detailed consideration of the effects of
outburst duration and geometrical scattering modifications due to finite
scattering dust filament dimension, inclination, and image point-spread
function and spectrograph slit width. In this paper, we explore the
implications of these factors and present a framework for future resolved
supernova light echo spectra interpretation, and test it against Cas A and SN
1987A light echo spectra. We conclude that the full modeling of the dimensions
and orientation of the scattering dust using the observed light echoes at two
or more epochs is critical for the correct interpretation of light echo
spectra. Indeed, without doing so one might falsely conclude that differences
exist when none are actually present.Comment: 18 pages, 22 figures, accepted for publication in Ap
The Luminous and Carbon-Rich Supernova 2006gz: A Double Degenerate Merger?
Spectra and light curves of SN 2006gz show the strongest signature of
unburned carbon and one of the slowest fading light curves ever seen in a type
Ia event (Delta m_15 = 0.69 +/- 0.04). The early-time Si II velocity is low,
implying it was slowed by an envelope of unburned material. Our best estimate
of the luminosity implies M_V = -19.74 and the production of ~ 1.2 M_sun of
56Ni. This suggests a super-Chandrasekhar mass progenitor. A double degenerate
merger is consistent with these observations.Comment: Accepted for publication in ApJL (5 pages, 4 figures). UBVr'i' light
curves, UVOIR light curves, and spectra available at
http://www.cfa.harvard.edu/supernova/SN2006g
Multidimensional supernova simulations with approximative neutrino transport. II. Convection and the advective-acoustic cycle in the supernova core
By 2D hydrodynamic simulations including a detailed equation of state and
neutrino transport, we investigate the interplay between different non-radial
hydrodynamic instabilities that play a role during the postbounce accretion
phase of collapsing stellar cores. The convective mode of instability, which is
driven by negative entropy gradients caused by neutrino heating or by time
variations of the shock strength, can be identified clearly by the development
of typical Rayleigh-Taylor mushrooms. However, in cases where the gas in the
postshock region is rapidly advected towards the gain radius, the growth of
such a buoyancy instability can be suppressed. In such a situation the shocked
flow nevertheless can develop non-radial asymmetry with an oscillatory growth
of the amplitude. This phenomenon has been termed ``standing accretion shock
instability'' (SASI). It is shown here that the SASI oscillations can trigger
convective instability and like the latter they lead to an increase of the
average shock radius and of the mass in the gain layer. Both hydrodynamic
instabilities in combination stretch the advection time of matter through the
neutrino-heating layer and thus enhance the neutrino energy deposition in
support of the neutrino-driven explosion mechanism. A rapidly contracting and
more compact nascent NS turns out to be favorable for explosions, because the
accretion luminosity and neutrino heating are larger and the growth rate of the
SASI is higher. Moreover, we show that the oscillation period of the SASI and a
variety of other features in our simulations agree with estimates for the
advective-acoustic cycle (AAC), in which perturbations are carried by the
accretion flow from the shock to the neutron star and pressure waves close an
amplifying global feedback loop. (abridged)Comment: 23 pages, 20 figures; revised version with extended Sect.5, accepted
by Astronomy & Astrophysics; high-resolution images can be obtained upon
reques
Nebular spectra from Type Ia supernova explosion models compared to JWST observations of SN 2021aefx
Context: Recent JWST observations of the Type Ia supernova (SN Ia) 2021aefx in the nebular phase have paved the way for late-time studies covering the full optical to mid-infrared (MIR) wavelength range, and with it the hope to better constrain SN Ia explosion mechanisms.
Aims: We investigate whether public SN Ia models covering a broad range of progenitor scenarios and explosion mechanisms (Chandrasekhar-mass, or MCh, delayed detonations, pulsationally assisted gravitationally confined detonations, sub-MCh double detonations, and violent mergers) can reproduce the full optical-MIR spectrum of SN 2021aefx at ∼270 days post explosion.
Methods: We consider spherically averaged 3D models available from the Heidelberg Supernova Model Archive with a 56Ni yield in the range 0.5–0.8 M⊙. We performed 1D steady-state non-local thermodynamic equilibrium simulations with the radiative-transfer code CMFGEN, and compared the predicted spectra to SN 2021aefx.
Results: The models can explain the main features of SN 2021aefx over the full wavelength range. However, no single model, or mechanism, emerges as a preferred match, and the predicted spectra are similar to each other despite the very different explosion mechanisms. We discuss possible causes for the mismatch of the models, including ejecta asymmetries and ionisation effects. Our new calculations of the collisional strengths for Ni III have a major impact on the two prominent lines at 7.35 μm and 11.00 μm, and highlight the need for more accurate collisional data for forbidden transitions. Using updated atomic data, we identify a strong feature due to [Ca IV] 3.21 μm, attributed to [Ni I] in previous studies. We also provide a tentative identification of a forbidden line due to [Ne II] 12.81 μm, whose peaked profile indicates the presence of neon all the way to the innermost region of the ejecta, as predicted for instance in violent merger models. Contrary to previous claims, we show that the [Ar III] 8.99 μm line can be broader in sub-MCh models compared to near-MCh models. Last, the total luminosity in lines of Ni is found to correlate strongly with the stable nickel yield, although ionisation effects can bias the inferred abundance.
Conclusions: Our models suggest that key physical ingredients are missing from either the explosion models, or the radiative-transfer post-processing, or both. Nonetheless, they also show the potential of the near- and MIR to uncover new spectroscopic diagnostics of SN Ia explosion mechanisms
A Case Study of Small Scale Structure Formation in 3D Supernova Simulations
It is suggested in observations of supernova remnants that a number of large-
and small-scale structures form at various points in the explosion.
Multidimensional modeling of core-collapse supernovae has been undertaken since
SN1987A, and both simulations and observations suggest/show that
Rayleigh-Taylor instabilities during the explosion is a main driver for the
formation of structure in the remnants.
We present a case study of structure formation in 3D in a \msol{15} supernova
for different parameters. We investigate the effect of moderate asymmetries and
different resolutions of the formation and morphology of the RT unstable
region, and take first steps at determining typical physical quantities (size,
composition) of arising clumps. We find that in this progenitor the major RT
unstable region develops at the He/OC interface for all cases considered. The
RT instabilities result in clumps that are overdense by 1-2 orders of magnitude
with respect to the ambient gas, have size scales on the level of a few % of
the remnant diameter, and are not diffused after the first yrs of the
remnant evolution, in the absence of a surrounding medium.Comment: 59 pages, 34 figure
Ecological assessment of groundwater ecosystems disturbed by recharge systems using organic matter quality, biofilm characteristics and bacterial diversity
International audienc
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