3,485,126 research outputs found
Listening in/To Germany, Pale Mother
Get PDFA newly restored version of Helma Sanders-Brahms’ 1980 film, Deutschland, bleiche Mutter (Germany, Pale Mother), was premiered in 2014 as a “Berlinale Classic”. This article reveals a complex composition of archival and (re)constructed sound that amplifies the film’s problematisation of the relationship between public history and private memory and the competing claims to authenticity and authority in telling the stories of the past
Observed Fractions of Core-Collapse Supernova Types and Initial Masses of their Single and Binary Progenitor Stars
Full text linkWe analyse observed fractions of core-collapse SN types from the Lick
Observatory SN Search, and we discuss corresponding implications for massive
star evolution. For a standard IMF, observed fractions of SN types cannot be
reconciled with expectations of single-star evolution. The mass range of WR
stars that shed their H envelopes via their own mass loss accounts for less
than half the observed fraction of SNeIbc. Progenitors of SNeIbc must extend to
a much lower range of initial masses than classical WR stars, and we argue that
most SNIbc and SNIIb progenitors must arise from binary Roche-lobe overflow.
SNeIc still trace higher mass and metallicity, because line-driven winds in the
WR stage remove the He layer and propel the transition from SNIb to Ic. Less
massive progenitors of SNeIb and IIb may not be classical WR stars; they may be
underluminous with weak winds, possibly hidden by overluminous mass-gainer
companions that appear as B[e] supergiants or related objects having aspherical
circumstellar material. The remaining SN types (II-P, II-L, and IIn) are
redistributed across the full range of initial mass. We consider direct
collapse to black holes without visible SNe, but find this problematic. Major
areas of remaining uncertainty are (1) the influence of binary separation,
rotation, and metallicity, (2) mass differences in progenitors of SNeIIn
compared to SNeII-L and II-P, and (3) SNeIc arising from single stars with
eruptive mass loss, its dependence on metallicity, and how it relates to
diversity within the SNIc subclass. (abridged)Comment: MNRAS accepted, 18 pages, 8 Figures, 1 color figur
Numerical models of collisions between core-collapse supernovae and circumstellar shells
Get PDFRecent observations of luminous Type IIn supernovae (SNe) provide compelling
evidence that massive circumstellar shells surround their progenitors. In this
paper we investigate how the properties of such shells influence the SN
lightcurve by conducting numerical simulations of the interaction between an
expanding SN and a circumstellar shell ejected a few years prior to core
collapse. Our parameter study explores how the emergent luminosity depends on a
range of circumstellar shell masses, velocities, geometries, and wind mass-loss
rates, as well as variations in the SN mass and energy. We find that the shell
mass is the most important parameter, in the sense that higher shell masses (or
higher ratios of M_shell/M_SN) lead to higher peak luminosities and higher
efficiencies in converting shock energy into visual light. Lower mass shells
can also cause high peak luminosities if the shell is slow or if the SN ejecta
are very fast, but only for a short time. Sustaining a high luminosity for
durations of more than 100 days requires massive circumstellar shells of order
10 M_sun or more. This reaffirms previous comparisons between pre-SN shells and
shells produced by giant eruptions of luminous blue variables (LBVs), although
the physical mechanism responsible for these outbursts remains uncertain. The
lightcurve shape and observed shell velocity can help diagnose the approximate
size and density of the circumstellar shell, and it may be possible to
distinguish between spherical and bipolar shells with multi-wavelength
lightcurves. These models are merely illustrative. One can, of course, achieve
even higher luminosities and longer duration light curves from interaction by
increasing the explosion energy and shell mass beyond values adopted here.Comment: Accepted for publication in MNRAS. Tables of numerical results (SN
lightcurves and velocities) to be published online. (Updated to fix figures
The Extreme Hosts of Extreme Supernovae
Full text linkWe use GALEX ultraviolet (UV) and optical integrated photometry of the hosts
of seventeen luminous supernovae (LSNe, having peak M_V < -21) and compare them
to a sample of 26,000 galaxies from a cross-match between the SDSS DR4 spectral
catalog and GALEX interim release 1.1. We place the LSNe hosts on the galaxy
NUV-r versus M_r color magnitude diagram (CMD) with the larger sample to
illustrate how extreme they are. The LSN hosts appear to favor low-density
regions of the galaxy CMD falling on the blue edge of the blue cloud toward the
low luminosity end. From the UV-optical photometry, we estimate the star
formation history of the LSN hosts. The hosts have moderately low star
formation rates (SFRs) and low stellar masses (M_*) resulting in high specific
star formation rates (sSFR). Compared with the larger sample, the LSN hosts
occupy low-density regions of a diagram plotting sSFR versus M_* in the area
having higher sSFR and lower M_*. This preference for low M_*, high sSFR hosts
implies the LSNe are produced by an effect having to do with their local
environment. The correlation of mass with metallicity suggests that perhaps
wind-driven mass loss is the factor that prevents LSNe from arising in
higher-mass, higher-metallicity hosts. The massive progenitors of the LSNe
(>100 M_sun), by appearing in low-SFR hosts, are potential tests for theories
of the initial mass function that limit the maximum mass of a star based on the
SFR.Comment: 8 pages, 3 figures, 2 tables, accepted to ApJ, amended references and
updated SN designation
SN 2006gy: was it really extra-ordinary?
Full text linkWe present an optical photometric and spectroscopic study of the very
luminous type IIn SN 2006gy for a time period spanning more than one year. In
photometry, a broad, bright (M_R~-21.7) peak characterizes all BVRI light
curves. Afterwards, a rapid luminosity fading is followed by a phase of slow
luminosity decline between day ~170 and ~237. At late phases (>237 days),
because of the large luminosity drop (>3 mag), only upper visibility limits are
obtained in the B, R and I bands. In the near-infrared, two K-band detections
on days 411 and 510 open new issues about dust formation or IR echoes
scenarios. At all epochs the spectra are characterized by the absence of broad
P-Cygni profiles and a multicomponent Halpha profile, which are the typical
signatures of type IIn SNe. After maximum, spectroscopic and photometric
similarities are found between SN 2006gy and bright, interaction-dominated SNe
(e.g. SN 1997cy, SN 1999E and SN 2002ic). This suggests that ejecta-CSM
interaction plays a key role in SN 2006gy about 6 to 8 months after maximum,
sustaining the late-time-light curve. Alternatively, the late luminosity may be
related to the radioactive decay of ~3M_sun of 56Ni. Models of the light curve
in the first 170 days suggest that the progenitor was a compact star (R~6-8
10^(12)cm, M_ej~5-14M_sun), and that the SN ejecta collided with massive
(6-10M_sun), opaque clumps of previously ejected material. These clumps do not
completely obscure the SN photosphere, so that at its peak the luminosity is
due both to the decay of 56Ni and to interaction with CSM. A supermassive star
is not required to explain the observational data, nor is an extra-ordinarily
large explosion energy.Comment: 33 pages, 8 figures. Accepted by ApJ. Paper with high-resolution
figures available at
http://web.oapd.inaf.it/supern/sn2006gy_astroph/agnoletto_2006gy.pd
SN 2009E: a faint clone of SN 1987A
Get PDFIn this paper we investigate the properties of SN 2009E, which exploded in a
relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest
1987A-like supernova discovered so far. Spectroscopic observations which
started about 2 months after the supernova explosion, highlight significant
differences between SN 2009E and the prototypical SN 1987A. Modelling the data
of SN 2009E allows us to constrain the explosion parameters and the properties
of the progenitor star, and compare the inferred estimates with those available
for the similar SNe 1987A and 1998A. The light curve of SN 2009E is less
luminous than that of SN 1987A and the other members of this class, and the
maximum light curve peak is reached at a slightly later epoch than in SN 1987A.
Late-time photometric observations suggest that SN 2009E ejected about 0.04
solar masses of 56Ni, which is the smallest 56Ni mass in our sample of
1987A-like events. Modelling the observations with a radiation hydrodynamics
code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an
initial radius of ~7 x 10^12 cm and an ejected mass of ~19 solar masses. The
photospheric spectra show a number of narrow (v~1800 km/s) metal lines, with
unusually strong Ba II lines. The nebular spectrum displays narrow emission
lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively
strong compared to the [Ca II] doublet. The overall spectroscopic evolution is
reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This
suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy
tail in the distribution of the 1987A-like objects in the same manner as SN
1997D and similar events represent the faint tail in the distribution of
physical properties for normal type II-plateau supernovae.Comment: 19 pages, 9 figures (+7 in appendix); accepted for publication in A&A
on 3 November 201
Hyperaccreting Disks around Magnetars for Gamma-Ray Bursts: Effects of Strong Magnetic Fields
Full text link(Abridged) The hyperaccreting neutron star or magnetar disks cooled via
neutrino emission can be a candidate of gamma-ray burst (GRB) central engines.
The strong field G of the magnetar can play a significant
role in affecting the disk properties and even lead to the funnel accretion
process. We investigate the effects of strong fields on the disks around
magnetars, and discuss implications of such accreting magnetar systems for GRB
and GRB-like events. We discuss quantum effects of the strong fields on the
disk, and use the MHD conservation equations to describe the behavior of the
disk flow coupled with a large scale field, which is generated by the star-disk
interaction. In general, stronger fields give higher disk densities, pressures,
temperatures and neutrino luminosity, and change the electron fraction and
degeneracy state significantly. A magnetized disk is always viscously stable
outside the Alfv\'{e}n radius, but will be thermally unstable near the
Alfv\'{e}n radius where the magnetic field plays a more important role in
transferring the angular momentum and heating the disk than the viscous stress.
The funnel accretion process will be only important for an extremely strong
field, which creates a magnetosphere inside the Alfv\'{e}n radius and truncates
the plane disk. Because of higher temperature and more concentrated neutrino
emission of the magnetar surface ring-like belt region covered by funnel
accretion, the neutrino annihilation rate from the accreting magnetars can be
much higher than that from accreting neutron stars without fields. Furthermore,
the neutrino annihilation mechanism and the magnetically-driven pulsar wind
from the magnetar surface can work together to generate and feed an
ultra-relativistic jet along the stellar magnetic poles.Comment: 62 pages, 14 figures, 4 tables, improved version following the
referee's comments, accepted for publication in Ap
The type IIn supernova 1994W: evidence for the explosive ejection of a circumstellar envelope
Full text linkWe present and analyse spectra of the Type IIn supernova 1994W obtained
between 18 and 203 days after explosion. During the luminous phase (first 100
d) the line profiles are composed of three major components: (i) narrow P-Cygni
lines with the absorption minima at -700 km/s; (ii) broad emission lines with
BVZI ~4000 km/s; and (iii) broad, smooth wings, most apparent in H-alpha. These
components are identified with an expanding circumstellar (CS) envelope,
shocked cool gas in the forward post-shock region, and multiple Thomson
scattering in the CS envelope, respectively. The absence of broad P-Cygni lines
from the supernova is the result of the formation of an optically thick, cool,
dense shell at the interface of the ejecta and the CS envelope. We model the
supernova deceleration and Thomson scattering wings to recover the density,
radial extent and Thomson optical depth of the CS envelope during the first
month. We reproduce the light curve with a hydrodynamical model and find it to
be powered by a combination of internal energy leakage after the explosion of
an extended pre-supernova (~10^15 cm) and luminosity from circumstellar
interaction. We recover the pre-explosion kinematics of the CS envelope: it is
close to homologous expansion with outer velocity ~1100 km/s and a kinematic
age of ~1.5 yr. The CS envelope's high mass and kinetic energy, combined with
its small age, strongly suggest that the CS envelope was explosively ejected
about 1.5 yr before the supernova explosion.Comment: 22 pages, 21 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Intracluster supernovae in the Multi-epoch Nearby Cluster Survey
Full text linkThe Multi-Epoch Nearby Cluster Survey (MENeaCS) has discovered twenty-three
cluster Type Ia supernovae (SNe) in the 58 X-ray selected galaxy clusters (0.05
< z < 0.15) surveyed. Four of our SN Ia events have no host galaxy on close
inspection, and are likely intracluster SNe. Deep image stacks at the location
of the candidate intracluster SNe put upper limits on the luminosities of faint
hosts, with M_{r} > -13.0 mag and M_{g} > -12.5 mag in all cases. For such
limits, the fraction of the cluster luminosity in faint dwarfs below our
detection limit is <0.1%, assuming a standard cluster luminosity function. All
four events occurred within ~600 kpc of the cluster center (projected), as
defined by the position of the brightest cluster galaxy, and are more centrally
concentrated than the cluster SN Ia population as a whole. After accounting for
several observational biases that make intracluster SNe easier to discover and
spectroscopically confirm, we calculate an intracluster stellar mass fraction
of 0.16^{+0.13}_{-0.09} (68% CL) for all objects within R_{200}. If we assume
that the intracluster stellar population is exclusively old, and the cluster
galaxies themselves have a mix of stellar ages, we derive an upper limit on the
intracluster stellar mass fraction of <0.47 (84% one-sided CL). When combined
with the intragroup SNe results of McGee & Balogh, we confirm the declining
intracluster stellar mass fraction as a function of halo mass reported by
Gonzalez and collaborators. (Abridged)Comment: 24 pages, 8 figures, ApJ publishe
Common Envelope Evolution Leading to Supernovae with Dense Interaction
Full text linkA variety of supernova events, including Type IIn supernovae and
ultraluminous supernovae, appear to have lost up to solar masses of their
envelopes in 10's to 100's of years leading up to the explosion. In order to
explain the close timing of the mass loss and supernova events, we explore the
possibility that the mass loss is driven by common envelope evolution of a
compact object (neutron star or black hole) in the envelope of a massive star
and the supernova is triggered by the inspiral of the compact object to the
central core of the companion star. The expected rate of such events is smaller
than the observed rate of Type IIn supernovae but the rates may agree within
the uncertainties. The mass loss velocity is related to the escape velocity
from the common envelope system and is comparable to the observed velocity of
100's of km s in Type IIn events. The mass loss is expected to be denser
near the equatorial plane of the binary system and there is good evidence that
the circumstellar media in Type IIn supernovae are asymmetric. Some of these
supernova types show evidence for energies in excess of the canonical
ergs, which might be the result of explosions from rapid accretion onto a
compact object through a disk.Comment: Small changes to agree with published version: ApJ Letters, 752, L2
(2012
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