351 research outputs found
Gamma-Rays as Probes for the Multi-Dimensionality of Type Ia Supernovae
We present -ray spectra for a set of Type Ia supernovae models. Our
study is based on a detailed Monte Carlo transport scheme for both spherical
and full 3-D geometries. Classical and new challenges of the ray
astronomy are addressed. We find that -rays are very suitable to
reveal the structure of the envelope and, thus, they allow to probe properties
of the nuclear burning front and the progenitor, namely its central density and
global asphericities. The potential problems are discussed for the quantitative
comparison between theoretical and observed line fluxes during the first few
months after the explosion.Comment: in Astronomy with Radioactivities,ed.R.Diehl,SpaceScienceRev.,in
pres
Near-infrared light curves of type Ia supernovae
Aims. With our time-dependent model atmosphere code PHOENIX, our goal is to
simulate light curves and spectra of hydrodynamical models of all types of
supernovae. In this work, we simulate near-infrared light curves of SNe Ia and
confirm the cause of the secondary maximum. Methods. We apply a simple energy
solver to compute the evolution of an SN Ia envelope during the free expansion
phase. Included in the solver are energy changes due to expansion, the energy
deposition of {\gamma}-rays and interaction of radiation with the material.
Results. We computed theoretical light curves of several SN Ia hydrodynamical
models in the I, J, H, and K bands and compared them to the observed SN Ia
light curves of SN 1999ee and SN 2002bo. By changing a line scattering
parameter in time, we obtained quite reasonable fits to the observed
near-infrared light curves. This is a strong hint that detailed NLTE effects in
IR lines have to be modeled, which will be a future focus of our work.
Conclusions. We found that IR line scattering is very important for the
near-infrared SN Ia light curve modeling. In addition, the recombination of Fe
III to Fe II and of Co III to Co II is responsible for the secondary maximum in
the near-infrared bands. For future work the consideration of NLTE for all
lines (including the IR subordinate lines) will be crucial.Comment: 5 pages, 12 figures, A&A in pres
VLT Spectropolarimetry of the fast expanding Type Ia SN2006X
Using VLT-FORS1 we performed optical spectropolarimetric observations of the
Type Ia SN2006X on 7 pre-maximum epochs (day -10 to day -1) and one
post-maximum epoch (+39 days). The SN shows strong continuum interstellar
polarization reaching about 8% at 4000A, characterized by a wavelength
dependency that is substantially different from that of the Milky-Way dust
mixture. Several SN features, like SiII 6355A and the CaII IR triplet, present
a marked evolution. The CaII near-IR triplet shows a pronounced polarization
(~1.4%) already on day -10 in correspondence with a strong high-velocity
feature (HVF). The SiII polarization peaks on day -6 at about 1.1% and
decreases to 0.8% on day -1. By day +39 no polarization signal is detected for
the SiII line, while the CaII IR triplet shows a marked re-polarization at the
level of 1.2%. As in the case of another strongly polarized SN (2004dt), no
polarization was detected across the OI 7774A absorption. The fast-expanding
SN2006X lies on the upper edge of the relation between peak polarization and
decline rate, and it confirms previous speculations about a correlation between
degree of polarization, expansion velocity, and HVF strength. The polarization
of CaII detected in our last epoch, the most advanced ever obtained for a Type
Ia SN, coincides in velocity with the outer boundary of the Ca synthesized
during the explosion (15,000-17,000 km/s) in delayed-detonation models. This
suggests a large scale chemical inhomogeneity as produced by off-center
detonations, a rather small amount of mixing, or a combination of both effects.
In contrast, the absence of polarization at the inner edge of the Ca-rich layer
(8000-10,000 km/s) implies a substantial amount of mixing in these deeper
regions.Comment: 28 pages, 39 figures, accepted for publication in Astronomy and
Astrophysic
Type Iax Supernovae
Type Iax supernovae (SN Iax), also called SN 2002cx-like supernovae, are the
largest class of peculiar white dwarf (thermonuclear) supernovae, with over
fifty members known. SN Iax have lower ejecta velocity and lower luminosities,
and these parameters span a much wider range, than normal type Ia supernovae
(SN Ia). SN Iax are spectroscopically similar to some SN Ia near maximum light,
but are unique among all supernovae in their late-time spectra, which never
become fully nebular. SN Iax overwhelmingly occur in late-type host galaxies,
implying a relatively young population. The SN Iax 2012Z is the only white
dwarf supernova for which a pre-explosion progenitor system has been detected.
A variety of models have been proposed, but one leading scenario has emerged: a
type Iax supernova may be a pure-deflagration explosion of a carbon-oxygen (or
hybrid carbon-oxygen-neon) white dwarf, triggered by helium accretion to the
Chandrasekhar mass, that does not necessarily fully disrupt the star.Comment: Author version of a chapter in the 'Handbook of Supernovae', edited
by A. Alsabti and P. Murdin, Springer. 31 pages, 6 figure
Synthetic Spectra for Type Ia Supernovae at Early Epochs
We present the current status of our construction of synthetic spectra for
type Ia supernovae. These properly take into account the effects of NLTE and an
adequate representation of line blocking and blanketing. The models are based
on a sophisticated atomic database. We show that the synthetic spectrum
reproduces the observed spectrum of 'normal' SN-Ia near maximum light from the
UV to the near-IR. However, further improvements are necessary before truly
quantitative analyses of observed SN-Ia spectra can be performed. In
particular, the inner boundary condition has to be fundamentally modified. This
is due to the dominance of electron scattering over true absorption processes
coupled with the flat density structure in these objectsComment: To appear in "Proceedings of the IAU Colloquium 192 - Supernovae (10
Years of SN1993J)", eds. J.M. Marcaide and K.W. Weile
Spectropolarimetry of the Type Ia SN 2007sr Two Months After Maximum Light
We present late time spectropolarimetric observations of SN 2007sr, obtained
with the VLT telescope at ESO Paranal Observatory when the object was 63 days
after maximum light. The late time spectrum displays strong line polarization
in the CaII absorption features. SN 2007sr adds to the case of some normal Type
Ia SNe that show high line polarization or repolarization at late times, a fact
that might be connected with the presence of high velocity features at early
times
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
A Catalog of Near Infrared Spectra from Type Ia Supernovae
We present forty-one near infrared (NIR, 0.7-2.5 microns) spectra from normal
Type Ia supernovae (SNe Ia) obtained at epochs ranging from fourteen days
before to seventy-five days with respect to the maximum light date in the
V-band. All data were obtained at the IRTF using the SpeX instrument. We
identify many spectral features, measure the Doppler velocities, and discuss
the chemical distribution of explosion products in SNe Ia. We describe
procedures for smoothing data, fitting continua, and measuring absorption
features to insure consistency for measurement and analysis.
This sample provides the first opportunity to examine and compare a large
number of SNe Ia in this wavelength region. NIR data are a rich source of
information about explosion products whose signatures are blended or obscured
in other spectral regions and NIR observations probe a greater radial depth
than optical wavelengths. We analyze similarities and differences in the
spectra and we show that the progressive development of spectral features for
normal SNe Ia in the NIR is consistent with time.
Measured Doppler velocities indicate that burning products in SNe Ia are
distributed in distinct layers with no large scale mixing. Carbon is not
detected in these data, in agreement with previous results with NIR data
establishing very low limits on carbon abundance in SNe Ia. Carbon burning
products, O and Mg, are plentiful in the outer layers suggesting that the
entire progenitor is burned in the explosion. The data provide a resource for
investigations of cross-correlations with other data libraries that may further
constrain SN Ia physics and improve the effectiveness of SNe Ia as cosmological
distance indicators.Comment: Accepted to The Astronomical Journal: 81 pages, 6 tables, 21 figure
- âŠ