39 research outputs found
Spectral modeling of type II supernovae. I. Dilution factors
We present substantial extensions to the Monte Carlo radiative transfer code
TARDIS to perform spectral synthesis for type II supernovae. By incorporating a
non-LTE ionization and excitation treatment for hydrogen, a full account of
free-free and bound-free processes, a self-consistent determination of the
thermal state and by improving the handling of relativistic effects, the
improved code version includes the necessary physics to perform spectral
synthesis for type II supernovae to high precision as required for the reliable
inference of supernova properties. We demonstrate the capabilities of the
extended version of TARDIS by calculating synthetic spectra for the
prototypical type II supernova SN1999em and by deriving a new and independent
set of dilution factors for the expanding photosphere method. We have
investigated in detail the dependence of the dilution factors on photospheric
properties and, for the first time, on changes in metallicity. We also compare
our results with two previously published sets of dilution factors by Eastman
et al. (1996) and by Dessart & Hillier (2005), and discuss the potential
sources of the discrepancies between studies.Comment: 16 pages, 12 figures, 2 tables, accepted for publication in A&
Early light curves for Type Ia supernova explosion models
Upcoming high-cadence transient survey programmes will produce a wealth of
observational data for Type Ia supernovae. These data sets will contain
numerous events detected very early in their evolution, shortly after
explosion. Here, we present synthetic light curves, calculated with the
radiation hydrodynamical approach Stella for a number of different explosion
models, specifically focusing on these first few days after explosion. We show
that overall the early light curve evolution is similar for most of the
investigated models. Characteristic imprints are induced by radioactive
material located close to the surface. However, these are very similar to the
signatures expected from ejecta-CSM or ejecta-companion interaction. Apart from
the pure deflagration explosion models, none of our synthetic light curves
exhibit the commonly assumed power-law rise. We demonstrate that this can lead
to substantial errors in the determination of the time of explosion. In
summary, we illustrate with our calculations that even with very early data an
identification of specific explosion scenarios is challenging, if only
photometric observations are available.Comment: 15 pages, 14 figures, 3 tables, accepted for publication in MNRA
Self-consistent modelling of line-driven hot-star winds with Monte Carlo radiation hydrodynamics
Radiative pressure exerted by line interactions is a prominent driver of
outflows in astrophysical systems, being at work in the outflows emerging from
hot stars or from the accretion discs of cataclysmic variables, massive young
stars and active galactic nuclei. In this work, a new radiation hydrodynamical
approach to model line-driven hot-star winds is presented. By coupling a Monte
Carlo radiative transfer scheme with a finite-volume fluid dynamical method,
line-driven mass outflows may be modelled self-consistently, benefiting from
the advantages of Monte Carlo techniques in treating multi-line effects, such
as multiple scatterings, and in dealing with arbitrary multidimensional
configurations. In this work, we introduce our approach in detail by
highlighting the key numerical techniques and verifying their operation in a
number of simplified applications, specifically in a series of self-consistent,
one-dimensional, Sobolev-type, hot-star wind calculations. The utility and
accuracy of our approach is demonstrated by comparing the obtained results with
the predictions of various formulations of the so-called CAK theory and by
confronting the calculations with modern sophisticated techniques of predicting
the wind structure. Using these calculations, we also point out some useful
diagnostic capabilities our approach provides. Finally we discuss some of the
current limitations of our method, some possible extensions and potential
future applications.Comment: 15 pages, 8 figures; accepted for publication in MNRA
Strongly lensed SNe Ia in the era of LSST: observing cadence for lens discoveries and time-delay measurements
The upcoming Large Synoptic Survey Telescope (LSST) will detect many strongly
lensed Type Ia supernovae (LSNe Ia) for time-delay cosmography. This will
provide an independent and direct way for measuring the Hubble constant ,
which is necessary to address the current tension in between
the local distance ladder and the early Universe measurements. We present a
detailed analysis of different observing strategies for the LSST, and quantify
their impact on time-delay measurement between multiple images of LSNe Ia. For
this, we produced microlensed mock-LSST light curves for which we estimated the
time delay between different images. We find that using only LSST data for
time-delay cosmography is not ideal. Instead, we advocate using LSST as a
discovery machine for LSNe Ia, enabling time delay measurements from follow-up
observations from other instruments in order to increase the number of systems
by a factor of 2 to 16 depending on the observing strategy. Furthermore, we
find that LSST observing strategies, which provide a good sampling frequency
(the mean inter-night gap is around two days) and high cumulative season length
(ten seasons with a season length of around 170 days per season), are favored.
Rolling cadences subdivide the survey and focus on different parts in different
years; these observing strategies trade the number of seasons for better
sampling frequency. In our investigation, this leads to half the number of
systems in comparison to the best observing strategy. Therefore rolling
cadences are disfavored because the gain from the increased sampling frequency
cannot compensate for the shortened cumulative season length. We anticipate
that the sample of lensed SNe Ia from our preferred LSST cadence strategies
with rapid follow-up observations would yield an independent percent-level
constraint on .Comment: 25 pages, 22 figures; accepted for publication in A&
The supernova impostor PSN J09132750+7627410 and its progenitor
We report the results of our follow-up campaign of the supernova impostor PSN
J09132750+7627410, based on optical data covering . From the
beginning, the transient shows prominent narrow Balmer lines with P-Cygni
profiles, with a blue-shifted absorption component becoming more prominent with
time. Along the of the spectroscopic monitoring, broad
components are never detected in the hydrogen lines, suggesting that these
features are produced in slowly expanding material. The transient reaches an
absolute magnitude at maximum, a typical
luminosity for supernova impostors. Amateur astronomers provided
of archival observations of the host galaxy, NGC 2748. The
detection of the quiescent progenitor star in archival images obtained with the
Hubble Space Telescope suggests it to be an \msun white-yellow
supergiant.Comment: 7 pages, 4 figures, supplemental material available in the source
file. Accepted for publication on Astrophysical Journal Letter
Massive stars exploding in a He-rich circumstellar medium - VIII. PSN J07285387+3349106, a highly reddened supernova Ibn
We present spectroscopic and photometric observations for the Type Ibn
supernova (SN) dubbed PSN J07285387+3349106. Using data provided by amateur
astronomers, we monitored the photometric rise of the SN to maximum light,
occurred on 2015 February 18.8 UT (JD(max,V) = 2457072.0 +- 0.8). PSN
J07285387+3349106 exploded in the inner region of an infrared luminous galaxy,
and is the most reddened SN Ibn discovered so far. We apply multiple methods to
derive the total reddening to the SN, and determine a total colour excess
E(B-V)(tot) = 0.99 +- 0.48 mag. Accounting for the reddening correction, which
is affected by a large uncertainty, we estimate a peak absolute magnitude of
M(V) = -20.30 +- 1.50. The spectra are dominated by continuum emission at early
phases, and He I lines with narrow P-Cygni profiles are detected. We also
identify weak Fe III and N II features. All these lines show an absorption
component which is blue-shifted by about 900-1000 km/s. The spectra also show
relatively broad He I line wings with low contrast, which extend to above 3000
km/s. From about 2 weeks past maximum, broad lines of O I, Mg II and the Ca II
near-infrared triplet are identified. The composition and the expansion
velocity of the circumstellar material, and the presence of He I and
alpha-elements in the SN ejecta indicate that PSN J07285387+3349106 was
produced by the core-collapse of a stripped-envelope star. We suggest that the
precursor was WNE-type Wolf-Rayet star in its dense, He-rich circumstellar
cocoon.Comment: 12 pages, 7 figures, 2 tables. Accepted for publication in MNRA
Fast evolving pair-instability supernova models: evolution, explosion, light curves
With an increasing number of superluminous supernovae (SLSNe) discovered, the question of their origin remains open and causes heated debates in the supernova community. Currently, there are three proposed mechanisms for SLSNe: (1) pair-instability supernovae (PISNe), (2) magnetar-driven supernovae and (3) models in which the supernova ejecta interacts with a circumstellar material ejected before the explosion. Based on current observations of SLSNe, the PISN origin has been disfavoured for a number of reasons. Many PISN models provide overly broad light curves and too reddened spectra, because of massive ejecta and a high amount of nickel. In the current study, we re-examine PISN properties using progenitor models computed with the GENEC code. We calculate supernova explosions with FLASH and light-curve evolution with the radiation hydrodynamics code STELLA. We find that high-mass models (200 and 250 Mâ) at relatively high metallicity (Z = 0.001) do not retain hydrogen in the outer layers and produce relatively fast evolving PISNe Type I and might be suitable to explain some SLSNe. We also investigate uncertainties in light-curve modelling due to codes, opacities, the nickel-bubble effect and progenitor structure and composition
Massive stars exploding in a He-rich circumstellar medium - VII. The metamorphosis of ASASSN-15ed from a narrow line Type Ibn to a normal Type Ib Supernova
We present the results of the spectroscopic and photometric monitoring campaign of ASASSN-15ed. The transient was discovered quite young by the All Sky Automated Survey for SuperNovae (ASAS-SN) survey. Amateur astronomers allowed us to sample the photometric SN evolution around maximum light, which we estimate to have occurred on JD = 2457087.4 ± 0.6 in the r band. Its apparent r-band magnitude at maximum was r = 16.91 ± 0.10, providing an absolute magnitude Mr â â20.04 ± 0.20, which is slightly more luminous than the typical magnitudes estimated for Type Ibn SNe. The post-peak evolution was well monitored, and the decline rate (being in most bands around 0.1 mag dâ1 during the first 25 d after maximum) is marginally slower than the average decline rates of SNe Ibn during the same time interval. The object was initially classified as a Type Ibn SN because early-time spectra were characterized by a blue continuum with superimposed narrow P-Cygni lines of HeâI, suggesting the presence of a slowly moving (1200â1500 km sâ1), He-rich circumstellar medium. Later on, broad P-Cygni HeâI lines became prominent. The inferred velocities, as measured from the minimum of the broad absorption components, were between 6000 and 7000 km sâ1. As we attribute these broad features to the SN ejecta, this is the first time we have observed the transition of a Type Ibn SN to a Type Ib SN
Spectral modeling of type II supernovae II. A machine learning approach to quantitative spectroscopic analysis
There are now hundreds of publicly available supernova spectral time series.
Radiative transfer modeling of this data gives insights into the physical
properties of these explosions such as the composition, the density structure,
or the intrinsic luminosity---this is invaluable for understanding the
supernova progenitors, the explosion mechanism, or for constraining the
supernova distance. However, a detailed parameter study of the available data
has been out of reach due to the high dimensionality of the problem coupled
with the still significant computational expense. We tackle this issue through
the use of machine-learning emulators, which are algorithms for
high-dimensional interpolation. These use a pre-calculated training dataset to
mimic the output of a complex code but with run times orders of magnitude
shorter. We present the application of such an emulator to synthetic type II
supernova spectra generated with the TARDIS radiative transfer code. The
results show that with a relatively small training set of 780 spectra we can
generate emulated spectra with interpolation uncertainties of less than one
percent. We demonstrate the utility of this method by automatic spectral
fitting of two well-known type IIP supernovae; as an exemplary application, we
determine the supernova distances from the spectral fits using the
tailored-expanding-photosphere method. We compare our results to previous
studies and find good agreement. This suggests that emulation of TARDIS spectra
can likely be used to perform automatic and detailed analysis of many transient
classes putting the analysis of large data repositories within reach.Comment: 18 pages, 13 figures, 3 tables, submitted to A&