27 research outputs found
Self-consistent 3D radiative transfer for kilonovae: directional spectra from merger simulations
We present three-dimensional radiative transfer calculations for the ejecta
from a neutron star merger that include line-by-line opacities for tens of
millions of bound-bound transitions, composition from an r-process nuclear
network, and time-dependent thermalization of decay products from individual
and decay reactions. In contrast to expansion opacities and
other wavelength-binned treatments, a line-by-line treatment enables us include
fluorescence effects and associate spectral features with the emitting and
absorbing lines of individual elements. We find variations in the synthetic
observables with both the polar and azimuthal viewing angles. The spectra
exhibit blended features with strong interactions by Ce III, Sr II, Y II, and
Zr II that vary with time and viewing direction. We demonstrate the importance
of wavelength-calibration of atomic data using a model with calibrated Sr, Y,
and Zr data, and find major differences in the resulting spectra, including a
better agreement with AT2017gfo. The synthetic spectra for near-polar
inclination show a feature at around 8000 A, similar to AT2017gfo. However,
they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005
M) as we take into account only the early ejecta. The comparatively
featureless spectra for equatorial observers gives a tentative prediction that
future observations of edge-on kilonovae will appear substantially different
from AT2017gfo. We also show that 1D models obtained by spherically averaging
the 3D ejecta lead to dramatically different direction-integrated luminosities
and spectra compared to full 3D calculations.Comment: 12 pages, 5 figures. Accepted by ApJ
Family dispute: do Type IIP supernova siblings agree on their distance?
Context: Type II supernovae provide a direct way to estimate distances
through the expanding photosphere method, which is independent of the cosmic
distance ladder. A recently introduced Gaussian process-based method allows for
a fast and precise modelling of spectral time series, which puts accurate and
computationally cheap Type II-based absolute distance determinations within
reach.
Aims: The goal of the paper is to assess the internal consistency of this new
modelling technique coupled with the distance estimation empirically, using the
spectral time series of supernova siblings, i.e. supernovae that exploded in
the same host galaxy.
Methods: We use a recently developed spectral emulator code, which is trained
on \textsc{Tardis} radiative transfer models and is capable of a fast maximum
likelihood parameter estimation and spectral fitting. After calculating the
relevant physical parameters of supernovae we apply the expanding photosphere
method to estimate their distances. Finally, we test the consistency of the
obtained values by applying the formalism of Bayes factors.
Results: The distances to four different host galaxies were estimated based
on two supernovae in each. The distance estimates are not only consistent
within the errors for each of the supernova sibling pairs, but in the case of
two hosts they are precise to better than 5\%.
Conclusions: Even though the literature data we used was not tailored for the
requirements of our analysis, the agreement of the final estimates shows that
the method is robust and is capable of inferring both precise and consistent
distances. By using high-quality spectral time series, this method can provide
precise distance estimates independent of the distance ladder, which are of
high value for cosmology.Comment: 20 pages, 20 figures, 6 tables, Accepted in A&
SN2018kzr: A Rapidly Declining Transient from the Destruction of a White Dwarf
We present SN2018kzr, the fastest declining supernova-like transient, second only to the kilonova, AT2017gfo. SN2018kzr is characterized by a peak magnitude of Mr = -17.98, a peak bolometric luminosity of ?1.4 & xfffd;& x5e0;10(43) erg s(?1), and a rapid decline rate of 0.48 & xfffd;& xfffd;0.03 mag day(?1) in the r band. The bolometric luminosity evolves too quickly to be explained by pure Ni-56 heating, necessitating the inclusion of an alternative powering source. Incorporating the spin-down of a magnetized neutron star adequately describes the lightcurve and we estimate a small ejecta mass of M-ej & xfffd;=& xfffd;0.10 & xfffd;& xfffd;0.05 M. Our spectral modeling suggests the ejecta is composed of intermediate mass elements including O, Si, and Mg and trace amounts of Fe-peak elements, which disfavors a binary neutron star merger. We discuss three explosion scenarios for SN2018kzr, given the low ejecta mass, intermediate mass element composition, and high likelihood of additional powering?the core collapse of an ultra-stripped progenitor, the accretion induced collapse (AIC) of a white dwarf, and the merger of a white dwarf and neutron star. The requirement for an alternative input energy source favors either the AIC with magnetar powering or a white dwarf?neutron star merger with energy from disk wind shocks
Structure Calculations in Nd III and U III Relevant for Kilonovae Modelling
The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of freshly synthesized nuclei. However, its luminosity, colour and spectra depend on the atomic opacities of the produced elements. In particular, opacities of lanthanides and actinides elements, due to their large density of boundâbound transitions, are fundamental. The current work focuses on atomic structure calculations for lanthanide and actinide ions, which are important in kilonovae modelling of ejecta spectra. Calculations for Nd III and U III, two representative rare-earth ions, were achieved. Our aim is to provide valuable insights for future opacity calculations for all heavy elements. We noticed that the opacity of U III is about an order of magnitude greater than the opacity of Nd III due to a higher density of levels in the case of the actinide
Structure Calculations in Nd III and U III Relevant for Kilonovae Modelling
Funding Information: Funding: This work was partially supported by the Fundação para a CiĂȘncia e Tecnologia (FCT), Portugal through the contract UIDP/50 0 07/2020 (LIP). R.F.S acknowledges the support from the ChETEC COST Action( CA16117) during his short-term scientific mission at GSI. A.F. and G.M.-P. acknowledge the support of the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation program (ERC Advanced Grant KILONOVA No. 885281). Funding Information: This work was partially supported by the Funda??o para a Ci?ncia e Tecnologia (FCT), Portugal through the contract UIDP/50 0 07/2020 (LIP). R.F.S acknowledges the support from the ChETEC COST Action( CA16117) during his short-term scientific mission at GSI. A.F. and G.M.-P. acknowledge the support of the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation program (ERC Advanced Grant KILONOVA No. 885281). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The detection of gravitational waves and electromagnetic signals from the neutron star merger GW170817 has provided evidence that these astrophysical events are sites where the r-process nucleosynthesis operates. The electromagnetic signal, commonly known as kilonova, is powered by the radioactive decay of freshly synthesized nuclei. However, its luminosity, colour and spectra depend on the atomic opacities of the produced elements. In particular, opacities of lanthanides and actinides elements, due to their large density of boundâbound transitions, are fundamental. The current work focuses on atomic structure calculations for lanthanide and actinide ions, which are important in kilonovae modelling of ejecta spectra. Calculations for Nd III and U III, two representative rare-earth ions, were achieved. Our aim is to provide valuable insights for future opacity calculations for all heavy elements. We noticed that the opacity of U III is about an order of magnitude greater than the opacity of Nd III due to a higher density of levels in the case of the actinide.publishersversionpublishe
Self-consistent 3D Radiative Transfer for Kilonovae: Directional Spectra from Merger Simulations
We present 3D radiative transfer calculations for the ejecta from a neutron star merger that include line-by-line opacities for tens of millions of boundâbound transitions, composition from an r -process nuclear network, and time-dependent thermalization of decay products from individual α and ÎČ ^â decay reactions. In contrast to expansion opacities and other wavelength-binned treatments, a line-by-line treatment enables us to include fluorescence effects and associate spectral features with the emitting and absorbing lines of individual elements. We find variations in the synthetic observables with both the polar and azimuthal viewing angles. The spectra exhibit blended features with strong interactions by Ce iii , Sr ii , Y ii , and Zr ii that vary with time and viewing direction. We demonstrate the importance of wavelength calibration of atomic data using a model with calibrated Sr, Y, and Zr data, and find major differences in the resulting spectra, including a better agreement with AT2017gfo. The synthetic spectra for a near-polar inclination show a feature at around 8000 Ă
, similar to AT2017gfo. However, they evolve on a more rapid timescale, likely due to the low ejecta mass (0.005 M _â ) as we take into account only the early ejecta. The comparatively featureless spectra for equatorial observers gives a tentative prediction that future observations of edge-on kilonovae will appear substantially different from AT2017gfo. We also show that 1D models obtained by spherically averaging the 3D ejecta lead to dramatically different direction-integrated luminosities and spectra compared to full 3D calculations
Modelling the ionisation state of Type Ia supernovae in the nebular-phase
The nebular spectra of Type Ia supernovae ( 100 days after
explosion) consist mainly of emission lines from singly- and doubly-ionised
Fe-group nuclei. However, theoretical models for many scenarios predict that
non-thermal ionisation leads to multiply-ionised species whose recombination
photons ionise and deplete Fe , resulting in negligible [Fe II] emission.
We investigate a method to determine the collisional excitation conditions from
[Fe II] line ratios independently from the ionisation state and find that it
cannot be applied to highly-ionised models due to the influence of
recombination cascades on Fe level populations. When the ionisation state
is artificially lowered, the line ratios (and excitation conditions) are too
similar to distinguish between explosion scenarios. We investigate changes to
the treatment of non-thermal energy deposition as a way to reconcile
over-ionised theoretical models with observations and find that a simple work
function approximation provides closer agreement with the data for sub-Mch
models than a detailed Spencer-Fano treatment with widely-used cross section
data. To quantify the magnitude of additional heating processes that would be
required to sufficiently reduce ionisation from fast leptons, we artificially
boost the rate of energy loss to free electrons. We find that the equivalent of
as much as an eight times increase to the plasma loss rate would be needed to
reconcile the sub-Mch model with observed spectra. Future studies could
distinguish between reductions in the non-thermal ionisation rates and
increased recombination rates, such as by clumping.Comment: 13 pages. Accepted by MNRA
Family dispute: do Type IIP supernova siblings agree on their distance?
20 pages, 20 figures, 6 tables, Accepted in A&AInternational audienceContext: Type II supernovae provide a direct way to estimate distances through the expanding photosphere method, which is independent of the cosmic distance ladder. A recently introduced Gaussian process-based method allows for a fast and precise modelling of spectral time series, which puts accurate and computationally cheap Type II-based absolute distance determinations within reach. Aims: The goal of the paper is to assess the internal consistency of this new modelling technique coupled with the distance estimation empirically, using the spectral time series of supernova siblings, i.e. supernovae that exploded in the same host galaxy. Methods: We use a recently developed spectral emulator code, which is trained on \textsc{Tardis} radiative transfer models and is capable of a fast maximum likelihood parameter estimation and spectral fitting. After calculating the relevant physical parameters of supernovae we apply the expanding photosphere method to estimate their distances. Finally, we test the consistency of the obtained values by applying the formalism of Bayes factors. Results: The distances to four different host galaxies were estimated based on two supernovae in each. The distance estimates are not only consistent within the errors for each of the supernova sibling pairs, but in the case of two hosts they are precise to better than 5\%. Conclusions: Even though the literature data we used was not tailored for the requirements of our analysis, the agreement of the final estimates shows that the method is robust and is capable of inferring both precise and consistent distances. By using high-quality spectral time series, this method can provide precise distance estimates independent of the distance ladder, which are of high value for cosmology