1,871 research outputs found
Optical Spectra of 73 Stripped-Envelope Core-Collapse Supernovae
We present 645 optical spectra of 73 supernovae (SNe) of Types IIb, Ib, Ic,
and broad-lined Ic. All of these types are attributed to the core collapse of
massive stars, with varying degrees of intact H and He envelopes before
explosion. The SNe in our sample have a mean redshift = 4200 km/s. Most of
these spectra were gathered at the Harvard-Smithsonian Center for Astrophysics
(CfA) between 2004 and 2009. For 53 SNe, these are the first published spectra.
The data coverage range from mere identification (1-3 spectra) for a few SNe to
extensive series of observations (10-30 spectra) that trace the spectral
evolution for others, with an average of 9 spectra per SN. For 44 SNe of the 73
SNe presented here, we have well-determined dates of maximum light to determine
the phase of each spectrum. Our sample constitutes the most extensive spectral
library of stripped-envelope SNe to date. We provide very early coverage (as
early as 30 days before V-band max) for photospheric spectra, as well as
late-time nebular coverage when the innermost regions of the SNe are visible
(as late as 2 years after explosion, while for SN1993J, we have data as late as
11.6 years). This data set has homogeneous observations and reductions that
allow us to study the spectroscopic diversity of these classes of stripped SNe
and to compare these to SNe associated with gamma-ray bursts. We undertake
these matters in follow-up papers.Comment: Published by the Astronomical Journal in May 2015. All spectra are
publicly available at the CfA SN archive:
http://www.cfa.harvard.edu/supernova/SNarchive.html . A companion paper on
constructing SNID templates based on these spectra is by Liu & Modjaz (2014)
and the resulting SNID templates are available from the NYU website:
http://cosmo.nyu.edu/SNYU/spectra
SN 2016coi (ASASSN-16fp): an energetic H-stripped core-collapse supernova from a massive stellar progenitor with large mass loss
We present comprehensive observations and analysis of the energetic
H-stripped SN 2016coi (a.k.a. ASASSN-16fp), spanning the -ray through
optical and radio wavelengths, acquired within the first hours to 420
days post explosion. Our campaign confirms the identification of He in the SN
ejecta, which we interpret to be caused by a larger mixing of Ni into the outer
ejecta layers. From the modeling of the broad bolometric light curve we derive
a large ejecta mass to kinetic energy ratio (, ). The small
[\ion{Ca}{ii}] \lam\lam7291,7324 to [\ion{O}{i}] \lam\lam6300,6364 ratio
(0.2) observed in our late-time optical spectra is suggestive of a large
progenitor core mass at the time of collapse. We find that SN 2016coi is a
luminous source of X-rays ( in the first
days post explosion) and radio emission ( at peak). These values are in line with those
of relativistic SNe (2009bb, 2012ap). However, for SN 2016coi we infer
substantial pre-explosion progenitor mass-loss with rate and a sub-relativistic shock
velocity , in stark contrast with relativistic SNe and similar
to normal SNe. Finally, we find no evidence for a SN-associated shock breakout
-ray pulse with energy . While we
cannot exclude the presence of a companion in a binary system, taken together,
our findings are consistent with a massive single star progenitor that
experienced large mass loss in the years leading up to core-collapse, but was
unable to achieve complete stripping of its outer layers before explosion.Comment: Submitted to ApJ. Main text: 21 pages; Appendix: 15 pages; 12 figure
Spectroscopy of High-Redshift Supernovae from the ESSENCE Project: The First Two Years
We present the results of spectroscopic observations of targets discovered
during the first two years of the ESSENCE project. The goal of ESSENCE is to
use a sample of ~200 Type Ia supernovae (SNe Ia) at moderate redshifts (0.2 < z
< 0.8) to place constraints on the equation of state of the Universe.
Spectroscopy not only provides the redshifts of the objects, but also confirms
that some of the discoveries are indeed SNe Ia. This confirmation is critical
to the project, as techniques developed to determine luminosity distances to
SNe Ia depend upon the knowledge that the objects at high redshift are the same
as the ones at low redshift. We describe the methods of target selection and
prioritization, the telescopes and detectors, and the software used to identify
objects. The redshifts deduced from spectral matching of high-redshift SNe Ia
with low-redshift SNe Ia are consistent with those determined from host-galaxy
spectra. We show that the high-redshift SNe Ia match well with low-redshift
templates. We include all spectra obtained by the ESSENCE project, including 52
SNe Ia, 5 core-collapse SNe, 12 active galactic nuclei, 19 galaxies, 4 possibly
variable stars, and 16 objects with uncertain identifications.Comment: 38 pages, 9 figures (many with multiple parts), submitted to A
Pushing the Boundaries of Conventional Core-Collapse Supernovae: The Extremely Energetic Supernova SN 2003ma
We report the discovery of a supernova (SN) with the highest apparent energy
output to date and conclude that it represents an extreme example of the Type
IIn subclass. The SN, which was discovered behind the Large Magellanic Cloud at
z = 0.289 by the SuperMACHO microlensing survey, peaked at M_R = -21.5 mag and
only declined by 2.9 mag over 4.7 years after the peak. Over this period, SN
2003ma had an integrated bolometric luminosity of 4 x 10^51 ergs, more than any
other SN to date. The radiated energy is close to the limit allowed by
conventional core-collapse explosions. Optical spectra reveal that SN 2003ma
has persistent single-peaked intermediate-width hydrogen lines, a signature of
interaction between the SN and a dense circumstellar medium. The light curves
show further evidence for circumstellar interaction, including a long plateau
with a shape very similar to the classic SN IIn 1988Z -- however, SN 2003ma is
ten times more luminous at all epochs. The fast velocity measured for the
intermediate-width H_alpha component (~6000 km/s) points towards an extremely
energetic explosion (> 10^52 ergs), which imparts a faster blast-wave speed to
the post-shock material and a higher luminosity from the interaction than is
observed in typical SNe IIn. Mid-infrared observations of SN 2003ma suggest an
infrared light echo is produced by normal interstellar dust at a distance ~0.5
pc from the SN.Comment: 21 pages, 15 figures, accepted for publication in Ap
Spectral Identification of an Ancient Supernova using Light Echoes in the LMC
We report the successful identification of the type of the supernova
responsible for the supernova remnant SNR 0509-675 in the Large Magellanic
Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to
classify outbursts associated with centuries-old remnants provides a new window
into several aspects of supernova research and is likely to be successful in
providing new constraints on additional LMC supernovae as well as their
historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of
echo light from SNR 0509-675 shows broad emission and absorption lines
consistent with a supernova (SN) spectrum. We create a spectral library
consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered
by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the
observed light echo spectrum using minimization as well as correlation
techniques, and we find that overluminous 91T-like SNe Ia with \dm15<0.9
match the observed spectrum best.Comment: 12 pages, 18 Figures, to be published in Ap
Acoustoelectric effects in quantum constrictions
A dc current induced in a quantum constriction by a traveling acoustic wave
(or by non-equilibrium ballistic phonons) is considered. We show that in many
important situations the effect is originated from acoustically-induced
scattering between the propagating and reflecting states in the constriction.
Two particular regimes corresponding to relatively high and low acoustic
frequencies are discussed. In the first regime, the acoustoelectric effect in a
smooth constriction can be understood by semi-classical considerations based on
local conservation laws. For the low frequency regime, we show that the
acousto-conductance is closely related to the zero field conductance. The
qualitative considerations are confirmed by numerical calculations both for
smooth and abrupt channels.Comment: 10 pages, RevTeX, 9 postscript figures, submitted to Phys. Rev.
Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae
We have coordinated Hubble Space Telescope photometry with ground-based
discovery for three supernovae: two SN Ia near z~0.5 (SN 1997ce, SN 1997cj) and
a third event at z=0.97 (SN 1997ck). The superb spatial resolution of HST
separates each supernova from its host galaxy and leads to good precision in
the light curves. The HST data combined with ground-based photometry provide
good temporal coverage. We use these light curves and relations between
luminosity, light curve shape, and color calibrated from low-z samples to
derive relative luminosity distances which are accurate to 10% at z~0.5 and 20%
at z=1. The redshift-distance relation is used to place constraints on the
global mean matter density, Omega_matter, and the normalized cosmological
constant, Omega_Lambda. When the HST sample is combined with the distance to SN
1995K (z=0.48), analyzed by the same precepts, it suggests that matter alone is
insufficient to produce a flat Universe. Specifically, for
Omega_matter+Omega_Lambda=1, Omega_matter is less than 1 with >95% confidence,
and our best estimate of Omega_matter is -0.1 +/- 0.5 if Omega_Lambda=0.
Although the present result is based on a very small sample whose systematics
remain to be explored, it demonstrates the power of HST measurements for high
redshift supernovae.Comment: Submitted to ApJ Letters, 3 figures, 1 plate, additional tabl
The Axially Symmetric Ejecta of Supernova 1987A
Extensive early observations proved that the ejecta of supernova 1987A (SN
1987A) are aspherical. Fifteen years after the supernova explosion, the Hubble
Space Telescope has resolved the rapidly expanding ejecta. The late-time images
and spectroscopy provide a geometrical picture that is consistent with early
observations and suggests a highly structured, axially symmetric geometry. We
present here a new synthesis of the old and new data. We show that the Bochum
event, presumably a clump of Ni, and the late-time image, the locus of
excitation by Ti, are most naturally accounted for by sharing a common
position angle of about 14\degree, the same as the mystery spot and early
speckle data on the ejecta, and that they are both oriented along the axis of
the inner circumstellar ring at 45\degree to the plane of the sky. We also
demonstrate that the polarization represents a prolate geometry with the same
position angle and axis as the early speckle data and the late-time image and
hence that the geometry has been fixed in time and throughout the ejecta. The
Bochum event and the Doppler kinematics of the [Ca II]/[O II] emission in
spatially resolved HST spectra of the ejecta can be consistently integrated
into this geometry. The radioactive clump is deduced to fall approximately
along the axis of the inner circumstellar ring and therefore to be redshifted
in the North whereas the [Ca II]/[O II] 7300 \AA emission is redshifted in the
South. We present a jet-induced model for the explosion and argue that such a
model can account for many of the observed asymmetries. In the jet models, the
oxygen and calcium are not expected to be distributed along the jet, but
primarily in an expanding torus that shares the plane and northern blue shift
of the inner circumstellar ring.Comment: To Appear in Ap
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