30 research outputs found
Type Ia Supernova Explosion Models
Because calibrated light curves of Type Ia supernovae have become a major
tool to determine the local expansion rate of the Universe and also its
geometrical structure, considerable attention has been given to models of these
events over the past couple of years. There are good reasons to believe that
perhaps most Type Ia supernovae are the explosions of white dwarfs that have
approached the Chandrasekhar mass, M_ch ~ 1.39 M_sun, and are disrupted by
thermonuclear fusion of carbon and oxygen. However, the mechanism whereby such
accreting carbon-oxygen white dwarfs explode continues to be uncertain. Recent
progress in modeling Type Ia supernovae as well as several of the still open
questions are addressed in this review. Although the main emphasis will be on
studies of the explosion mechanism itself and on the related physical
processes, including the physics of turbulent nuclear combustion in degenerate
stars, we also discuss observational constraints.Comment: 38 pages, 4 figures, Annual Review of Astronomy and Astrophysics, in
pres
The Supernova Gamma-Ray Burst Connection
The chief distinction between ordinary supernovae and long-soft gamma-ray
bursts (GRBs) is the degree of differential rotation in the inner several solar
masses when a massive star dies, and GRBs are rare mainly because of the
difficulty achieving the necessary high rotation rate. Models that do provide
the necessary angular momentum are discussed, with emphasis on a new single
star model whose rapid rotation leads to complete mixing on the main sequence
and avoids red giant formation. This channel of progenitor evolution also gives
a broader range of masses than previous models, and allows the copious
production of bursts outside of binaries and at high redshifts. However, even
the production of a bare helium core rotating nearly at break up is not, by
itself, a sufficient condition to make a gamma-ray burst. Wolf-Rayet mass loss
must be low, and will be low in regions of low metallicity. This suggests that
bursts at high redshift (low metallicity) will, on the average, be more
energetic, have more time structure, and last longer than bursts nearby. Every
burst consists of three components: a polar jet (~0.1 radian), high energy,
subrelativistic mass ejection (~1 radian), and low velocity equatorial mass
that can fall back after the initial explosion. The relative proportions of
these three components can give a diverse assortment of supernovae and high
energy transients whose properties may vary with redshift.Comment: 10 pages, to appear in AIP Conf. Proc. "Gamma Ray Bursts in the Swift
Era", Eds. S. S. Holt, N. Gehrels, J. Nouse
Optical and spectral observations and hydrodynamic modelling of type IIb supernova 2017gpn
In this work we present the photometric and spectroscopic observations of type IIb supernova 2017gpn. This supernova was discovered in the error-box of the LIGO/Virgo G299232 gravitational-wave event. We obtained the light curves in the B and R passbands and modelled them numerically using the one-dimensional radiation hydrocode STELLA. The best-fitting model has the following parameters: the pre-SN star mass and the radius are M â 3.5 Mâ and R â 50 Râ, respectively; the explosion energy is Eexpâ1.2Ă1051 erg; the mass of radioactive nickel is M56Niâ0.11 Mâ, which is completely mixed throughout the ejecta; and the mass of the hydrogen envelope MH_env â 0.06 Mâ. Moreover, SN 2017gpn is a confirmed SN IIb that is located at the farthest distance from the centre of its host galaxy NGC 1343 (i.e. the projected distance is âŒ21 kpc). This challenges the scenario of the origin of type IIb supernovae from massive stars
Hierarchies of Susy Splittings and Invisible Photinos as Dark Matter
We explore how to generate hierarchies in the splittings between
superpartners. Some of the consequences are the existence of invisible
components of dark matter, new inflaton candidates, invisible monopoles and a
number of invisible particles that might dominate during various eras, in
particular between BBN and recombination and decay subsequently.Comment: 16 pages. v3: Ref. 27 has been modified. v4: Published versio
The Explosion Mechanism of Core-Collapse Supernovae and Its Observational Signatures
The death of massive stars is shrouded in many mysteries. One of them is the
mechanism that overturns the collapse of the degenerate iron core into an
explosion, a process that determines the supernova explosion energy, properties
of the surviving compact remnant, and the nucleosynthetic yields. The number of
core-collapse supernova observations has been growing with an accelerating pace
thanks to modern time-domain astronomical surveys and new tests of the
explosion mechanism are becoming possible. We review predictions of
parameterized supernova explosion models and compare them with explosion
properties inferred from observed light curves, spectra, and neutron star
masses.Comment: Reviews in Frontiers of Modern Astrophysics; From Space Debris to
Cosmology, edited by Kab\'ath, Petr; Jones, David; Skarka, Marek. ISBN:
978-3-030-38509-5. Cham: Springer International Publishing, 2020, pp. 189-21
The delay of shock breakout due to circumstellar material evident in most type II supernovae
Type II supernovae (SNe II) originate from the explosion of hydrogen-rich supergiant massive stars. Their first electromagnetic signature is the shock breakout (SBO), a short-lived phenomenon that can last for hours to days depending on the density at shock emergence. We present 26 rising optical light curves of SN II candidates discovered shortly after explosion by the High Cadence Transient Survey and derive physical parameters based on hydrodynamical models using a Bayesian approach. We observe a steep rise of a few days in 24 out of 26 SN II candidates, indicating the systematic detection of SBOs in a dense circumstellar matter consistent with a mass loss rate of M Ë â>â10â4Mââyrâ1 or a dense atmosphere. This implies that the characteristic hour-timescale signature of stellar envelope SBOs may be rare in nature and could be delayed into longer-lived circumstellar material SBOs in most SNe II
Light-curve and spectral properties of ultra-stripped core-collapse supernovae leading to binary neutron stars
We investigate light-curve and spectral properties of ultra-stripped core-collapse supernovae. Ultra-stripped supernovae are the explosions of heavily stripped massive stars which lost their envelopes via binary interactions with a compact companion star. They eject only âŒ0.1~Mâ and may be the main way to form double neutron-star systems which eventually merge emitting strong gravitational waves. We follow the evolution of an ultra-stripped supernova progenitor until iron core collapse and perform explosive nucleosynthesis calculations. We then synthesize light curves and spectra of ultra-stripped supernovae using the nucleosynthesis results and present their expected properties. Ultra-stripped supernovae synthesize âŒ0.01~Mâ of radioactive 56Ni, and their typical peak luminosity is around 1042~erg~sâ1 or â16 mag. Their typical rise time is 5 â 10 days. Comparing synthesized and observed spectra, we find that SN 2005ek, some of the so-called calcium-rich gap transients, and SN 2010X may be related to ultra-stripped supernovae. If these supernovae are actually ultra-stripped supernovae, their event rate is expected to be about 1 per cent of core-collapse supernovae. Comparing the double neutron-star merger rate obtained by future gravitational-wave observations and the ultra-stripped supernova rate obtained by optical transient surveys identified with our synthesized light-curve and spectral models, we will be able to judge whether ultra-stripped supernovae are actually a major contributor to the binary neutron star population and provide constraints on binary stellar evolution