45 research outputs found
Limits on stable iron in TypeIa supernovae from NIR spectroscopy
We obtained optical and near-infrared spectra of TypeIa supernovae
(SNeIa) at epochs ranging from 224 to 496 days after the explosion. The
spectra show emission lines from forbidden transitions of singly ionised iron
and cobalt atoms. We used non-local thermodynamic equilibrium (NLTE) modelling
of the first and second ionisation stages of iron, nickel, and cobalt to fit
the spectra using a sampling algorithm allowing us to probe a broad parameter
space. We derive velocity shifts, line widths, and abundance ratios for iron
and cobalt. The measured line widths and velocity shifts of the singly ionised
ions suggest a shared emitting region. Our data are fully compatible with
radioactive Ni decay as the origin for cobalt and iron. We compare the
measured abundance ratios of iron and cobalt to theoretical predictions of
various SNIa explosion models. These models include, in addition to
Ni, different amounts of Ni and stable Fe. We can
exclude models that produced only Fe or only Ni in addition to
Ni. If we consider a model that has Ni, Ni, and
Fe then our data imply that these ratios are Fe / Ni
and Ni / Ni .Comment: 10 pages, 7 figures, Accepted for publication in A&
Nebular spectroscopy of SN 2014J: Detection of stable nickel in near infrared spectra
We present near infrared (NIR) spectroscopy of the nearby supernova 2014J
obtained 450 d after explosion. We detect the [Ni II] 1.939 m line
in the spectra indicating the presence of stable Ni in the ejecta. The
stable nickel is not centrally concentrated but rather distributed as the iron.
The spectra are dominated by forbidden [Fe II] and [Co II] lines. We use lines,
in the NIR spectra, arising from the same upper energy levels to place
constraints on the extinction from host galaxy dust. We find that that our data
are in agreement with the high and low found in earlier studies
from data near maximum light. Using a Ni mass prior from near maximum
light -ray observations, we find 0.05 M of stable nickel
to be present in the ejecta. We find that the iron group features are
redshifted from the host galaxy rest frame by 600 km s.Comment: 6 pages, 4 figures, submitted to A&
Light curves of hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically
confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar
Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe
Ic-BL, on average, by about 4 and 2~mag, respectively. The peak absolute
magnitudes of SLSNe-I in rest-frame band span ~mag, and these peaks are not powered by radioactive Ni,
unless strong asymmetries are at play. The rise timescales are longer for SLSNe
than for normal SNe Ib/c, by roughly 10 days, for events with similar decay
times. Thus, SLSNe-I can be considered as a separate population based on
photometric properties. After peak, SLSNe-I decay with a wide range of slopes,
with no obvious gap between rapidly declining and slowly declining events. The
latter events show more irregularities (bumps) in the light curves at all
times. At late times, the SLSN-I light curves slow down and cluster around the
Co radioactive decay rate. Powering the late-time light curves with
radioactive decay would require between 1 and 10 of Ni masses.
Alternatively, a simple magnetar model can reasonably fit the majority of
SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay
of Co, up to days from explosion. The resulting spin values do
not correlate with the host-galaxy metallicities. Finally, the analysis of our
sample cannot strengthen the case for using SLSNe-I for cosmology.Comment: 120 pages, 48 figures, 78 tables. ApJ in pres
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
Opacities of Singly and Doubly Ionised Neodymium and Uranium for Kilonova Emission Modeling
Even though the electromagnetic counterpart AT2017gfo to the binary neutron
star merger GW170817 is powered by the radioactive decay of r-process nuclei,
only few tentative identifications of light r-process elements have been made
so far. One of the major limitations for the identification of heavy nuclei is
incomplete or missing atomic data. While substantial progress has been made on
lanthanide atomic data over the last few years, for actinides there has been
less emphasis, with the first complete set of opacity data only recently
published. We perform atomic structure calculations of neodymium as
well as the corresponding actinide uranium . Using two different codes
(FAC and HFR) for the calculation of the atomic data, we investigate the
accuracy of the calculated data (energy levels and electric dipole transitions)
and their effect on kilonova opacities. For the FAC calculations, we optimise
the local central potential and the number of included configurations and use a
dedicated calibration technique to improve the agreement between theoretical
and available experimental atomic energy levels (AELs). For ions with vast
amounts of experimental data available, the presented opacities agree quite
well with previous estimations. On the other hand, the optimisation and
calibration method cannot be used for ions with only few available AELs. For
these cases, where no experimental nor benchmarked calculations are available,
a large spread in the opacities estimated from the atomic data obtained with
the various atomic structure codes is observed.We find that the opacity of
uranium is almost double the neodymium opacity.Comment: 20 pages, 13 figures. Accepted by MNRA
Light curves of hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory
We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory (PTF) survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average by about 4 and 2 mag, respectively. The SLSNe-I peak absolute magnitudes in rest-frame -band span mag, and these peaks are not powered by radioactive Ni, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be considered as a separate population based on a photometric criterion. After peak, SLSNe-I decay with a wide range of slopes, with no obvious gap between rapidly-declining and slowly-declining events. The latter events show more irregularities (bumps) in the light curves at all times. At late times the SLSN-I light curves slow down and cluster around the Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10 of Ni masses. Alternatively, a simple magnetar model can reasonably fit the majority of SLSNe-I light curves, with three exceptions, and can mimic the radioactive decay of Co, up to days from explosion. The resulting spin values do not correlate with the host-galaxy metallicities. Finally, the analysis of our sample cannot strengthen the case for using SLSNe-I for cosmology
The rise and fall of an extraordinary Ca-rich transient: The discovery of ATLAS19dqr/SN 2019bkc
This work presents the observations and analysis of ATLAS19dqr/SN 2019bkc, an extraordinary rapidly evolving transient event located in an isolated environment, tens of kiloparsecs from any likely host. Its light curves rise to maximum light in 5-6 d and then display a decline of Îm15 ⌠5 mag. With such a pronounced decay, it has one of the most rapidly evolving light curves known for a stellar explosion. The early spectra show similarities to normal and "ultra-stripped" type Ic SNe, but the early nebular phase spectra, which were reached just over two weeks after explosion, display prominent calcium lines, marking SN 2019bkc as a Ca-rich transient. The Ca emission lines at this phase show an unprecedented and unexplained blueshift of 10 000-12 000 km s-1. Modelling of the light curve and the early spectra suggests that the transient had a low ejecta mass of 0.2-0.4 Mâ and a low kinetic energy of (2-4) Ă 1050 erg, giving a specific kinetic energy Ek/Mej ⌠1 [1051 erg]/Mâ. The origin of this event cannot be unambiguously defined. While the abundance distribution used to model the spectra marginally favours a progenitor of white dwarf origin through the tentative identification of Ar II, the specific kinetic energy, which is defined by the explosion mechanism, is found to be more similar to an ultra-stripped core-collapse events. SN 2019bkc adds to the diverse range of physical properties shown by Ca-rich events. © ESO 2020
Panning for gold, but finding helium: discovery of the ultra-stripped supernova SN2019wxt from gravitational-wave follow-up observations
We present the results from multi-wavelength observations of a transient
discovered during the follow-up of S191213g, a gravitational wave (GW) event
reported by the LIGO-Virgo Collaboration as a possible binary neutron star
merger in a low latency search. This search yielded SN2019wxt, a young
transient in a galaxy whose sky position (in the 80\% GW contour) and distance
(150\,Mpc) were plausibly compatible with the localisation uncertainty of
the GW event. Initially, the transient's tightly constrained age, its
relatively faint peak magnitude (\,mag) and the band
decline rate of \,mag per 5\,days appeared suggestive of a compact
binary merger. However, SN2019wxt spectroscopically resembled a type Ib
supernova, and analysis of the optical-near-infrared evolution rapidly led to
the conclusion that while it could not be associated with S191213g, it
nevertheless represented an extreme outcome of stellar evolution. By modelling
the light curve, we estimated an ejecta mass of , with
Ni comprising of this. We were broadly able to reproduce its
spectral evolution with a composition dominated by helium and oxygen, with
trace amounts of calcium. We considered various progenitors that could give
rise to the observed properties of SN2019wxt, and concluded that an
ultra-stripped origin in a binary system is the most likely explanation.
Disentangling electromagnetic counterparts to GW events from transients such as
SN2019wxt is challenging: in a bid to characterise the level of contamination,
we estimated the rate of events with properties comparable to those of
SN2019wxt and found that such event per week can occur within the
typical GW localisation area of O4 alerts out to a luminosity distance of
500\,Mpc, beyond which it would become fainter than the typical depth of
current electromagnetic follow-up campaigns.Comment: By the ENGRAVE collaboration (engrave-eso.org). 35 pages, 20 figures,
final version accepted by A&
The rise and fall of an extraordinary Ca-rich transient The discovery of ATLAS19dqr/SN 2019bkc
This work presents the observations and analysis of ATLAS19dqr/SN 2019bkc, an extraordinary rapidly evolving transient event located in an isolated environment, tens of kiloparsecs from any likely host. Its light curves rise to maximum light in 5-6 d and then display a decline of Delta m(15)similar to 5 mag. With such a pronounced decay, it has one of the most rapidly evolving light curves known for a stellar explosion. The early spectra show similarities to normal and "ultra-stripped" type Ic SNe, but the early nebular phase spectra, which were reached just over two weeks after explosion, display prominent calcium lines, marking SN 2019bkc as a Ca-rich transient. The Ca emission lines at this phase show an unprecedented and unexplained blueshift of 10 000-12 000 km s(-1). Modelling of the light curve and the early spectra suggests that the transient had a low ejecta mass of 0.2-0.4 M-circle dot and a low kinetic energy of (2-4) x 10(50) erg, giving a specific kinetic energy E-k/M-ej similar to 1 [10(51) erg]/M-circle dot. The origin of this event cannot be unambiguously defined. While the abundance distribution used to model the spectra marginally favours a progenitor of white dwarf origin through the tentative identification of ArII, the specific kinetic energy, which is defined by the explosion mechanism, is found to be more similar to an ultra-stripped core-collapse events. SN 2019bkc adds to the diverse range of physical properties shown by Ca-rich events
The evolution of luminous red nova AT 2017jfs in NGC 4470
We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of M-g = 15.46 +/- 0.15 mag and a bolometric luminosity of 5.5 x 10(41) erg s(-1). Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1