Abstract
The classification of stripped-envelope supernovae (SE-SNe) is revisited using modern data sets. Spectra are analysed using an empirical method to ‘blindly’ categorize SNe according to ...spectral feature strength and appearance. This method makes a clear distinction between SNe that are He-rich (IIb/Ib) and He-poor (Ic), and further analysis is performed on each subgroup. For He-rich SNe, the presence of H becomes the focus. The strength, velocity, and ratio between absorption and emission of H α are measured, along with additional analysis of He I lines, in order to categorize the SNe. The He-poor SNe are ordered according to the number of absorption features N present in the spectra, which is a measure of the degree of line blending. The kinetic energy per unit mass E
k/M
ej is strongly affected by mass at high velocity, and such situations principally occur when the outer density profile of the ejecta is shallow, leading to the blending of lines. Using the results, the existing SE-SN taxonomic scheme is adapted. He-rich SNe are split into four groups, IIb, IIb(I), Ib(II) and Ib, which represent H-rich to H-poor SNe. The SNe Ic category of broad-lined Ic (Ic-BL) is abandoned in favour of quantifying the line blending via 〈N〉 before peak. To better reflect the physical parameters of the explosions, the velocity of Si Uii at peak and the half-luminosity decay time t
+1/2 are included to give SNe Ic a designation of Ic-〈N〉(v
p, SiII/t
+1/2).
The optical and optical/near-infrared pseudo-bolometric light curves of 85 stripped-envelope supernovae (SNe) are constructed using a consistent method and a standard cosmology. The light curves are ...analysed to derive temporal characteristics and peak luminosity L
p, enabling the construction of a luminosity function. Subsequently, the mass of 56Ni synthesized in the explosion, along with the ratio of ejecta mass to ejecta kinetic energy, are found. Analysis shows that host-galaxy extinction is an important factor in accurately determining luminosity values as it is significantly greater than Galactic extinction in most cases. It is found that broad-lined SNe Ic (SNe Ic-BL) and gamma-ray burst SNe are the most luminous subtypes with a combined median L
p, in erg s−1, of log(L
p) = 43.00 compared to 42.51 for SNe Ic, 42.50 for SNe Ib, and 42.36 for SNe IIb. It is also found that SNe Ic-BL synthesize approximately twice the amount of 56Ni compared with SNe Ic, Ib, and IIb, with median M
Ni = 0.34, 0.16, 0.14, and 0.11 M⊙, respectively. SNe Ic-BL, and to a lesser extent SNe Ic, typically rise from L
p/2 to L
p more quickly than SNe Ib/IIb; consequently, their light curves are not as broad.
Luminosity distributions of Type Ia supernovae Ashall, C; Mazzali, P; Sasdelli, M ...
Monthly notices of the Royal Astronomical Society,
08/2016, Letnik:
460, Številka:
4
Journal Article
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We have assembled a data set of 165 low redshift, z < 0.06, publicly available Type Ia supernovae (SNe Ia). We produce maximum light magnitude (MB
and MV
) distributions of SNe Ia to explore the ...diversity of parameter space that they can fill. Before correction for host galaxy extinction we find that the mean MB
and MV
of SNe Ia are −18.58 ± 0.07 and −18.72 ± 0.05 mag, respectively. Host galaxy extinction is corrected using a new method based on the SN spectrum. After correction, the mean values of MB
and MV
of SNe Ia are −19.10 ± 0.06 and −19.10 ± 0.05 mag, respectively. After correction for host galaxy extinction, ‘normal’ SNe Ia (Δm
15(B) < 1.6 mag) fill a larger parameter space in the width–luminosity relation than previously suggested, and there is evidence for luminous SNe Ia with large Δm
15(B). We find a bimodal distribution in Δm
15(B), with a pronounced lack of transitional events at Δm
15(B) = 1.6 mag. We confirm that faster, low-luminosity SNe tend to come from passive galaxies. Dividing the sample by host galaxy type, SNe Ia from star-forming (S-F) galaxies have a mean MB
= −19.20 ± 0.05 mag, while SNe Ia from passive galaxies have a mean MB
= −18.57 ± 0.24 mag. Even excluding fast declining SNe, ‘normal’ (MB
< −18 mag) SNe Ia from S-F and passive galaxies are distinct. In the V band, there is a difference of 0.4 ± 0.13 mag between the median (MV
) values of the ‘normal’ SN Ia population from passive and S-F galaxies. This is consistent with (∼15 ± 10) per cent of ‘normal’ SNe Ia from S-F galaxies coming from an old stellar population.
We present the ATLAS discovery and initial analysis of the first 18 days of the unusual transient event, ATLAS18qqn/AT2018cow. It is characterized by a high peak luminosity (∼1.7 × 1044 erg s−1), ...rapidly evolving light curves (>5 mag rise to peak in ∼3.5 days), and hot blackbody spectra, peaking at ∼27,000 K that are relatively featureless and unchanging over the first two weeks. The bolometric light curve cannot be powered by radioactive decay under realistic assumptions. The detection of high-energy emission may suggest a central engine as the powering source. Using a magnetar model, we estimated an ejected mass of 0.1-0.4 M , which lies between that of low-energy core-collapse events and the kilonova, AT2017gfo. The spectra cooled rapidly from 27,000 to 15,000 K in just over two weeks but remained smooth and featureless. Broad and shallow emission lines appear after about 20 days, and we tentatively identify them as He i although they would be redshifted from their rest wavelengths. We rule out that there are any features in the spectra due to intermediate mass elements up to and including the Fe group. The presence of r-process elements cannot be ruled out. If these lines are due to He, then we suggest a low-mass star with residual He as a potential progenitor. Alternatively, models of magnetars formed in neutron star mergers, or accretion onto a central compact object, give plausible matches to the data.
We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen-poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory 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 g band span −22 Mg −20 mag, and these peaks are not powered by radioactive 56Ni, 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 56Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10 M 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 56Co, up to ∼400 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.
ABSTRACT
This work examines the relationships between the properties (flux ratios, full width at half-maximum velocities) of the O i λλ6300, 6364, Ca ii λλ7291, 7323, and the Ca ii near-infrared ...triplet, emission lines of a large sample of core-collapse supernovas (SNe) and Ca-rich transients (509 spectra of 86 transients, of which 10 transients are Ca-rich events). Line-flux ratios as a function of time were investigated with differences identified between the transient classes, in particular the Type II SNe were found to have distinct line-flux ratios compared to stripped-envelope (SE) SNe. No correlation was found between the Ca ii/O i flux ratios of SE-SNe and their ejecta masses and kinetic energies (as measured from light-curve modelling), suggesting that there may be a contribution from an additional power source in more luminous SE-SNe. We found that the mean characteristic width of the Ca ii emission line is less than the O i emission line for all SN types, indicating that the Ca ii emission typically originates from deeper in the ejecta than O i. This is in some tension with standard models for emission in Type II SNe. The emission line properties of Type II SNe were also compared to theoretical models and found to favour lower mass tracks (MZAMS< 15 M⊙), with no evidence found for significant mixing of 56Ni into the H envelope nor Ca mixed into the O shell. The flux ratios of some superluminous SNe were found to be similar to those of SE-SNe when scaling to account for their longer rise times was applied (although we caution the sample size is small).
ABSTRACT
At the age of about 1 yr, the spectra of most Type Ia supernovae (SNe Ia) are dominated by strong forbidden nebular emission lines of Fe ii and Fe iii. Later observations (at about 2 yr) of ...the nearby SN 2011fe showed an unexpected shift of ionization to Fe i and Fe ii. Spectra of the very nearby SN Ia 2014J at an intermediate phase (1–1.5 yr) that are presented here show a progressive decline of Fe iii emission, while Fe i is not yet strong. The decrease in ionization can be explained if the degree of clumping in the ejecta increases significantly at ∼1.5 yr, at least in the Fe-dominated zone. Models suggest that clumps remain coherent after about one year, behaving like shrapnel. The high density in the clumps, combined with the decreasing heating rate, would then cause recombination. These data may witness the phase of transition from relatively smooth ejecta to the very clumpy morphology that is typical of SN remnants. The origin of the increased clumping may be the development of local magnetic fields.
Bacillus Calmette-Guérin (BCG) vaccination induces variable protection against pulmonary tuberculosis (TB), and a more effective TB vaccine is needed. The potential for BCG to provide protection ...against heterologous infections, by induction of innate immune memory, is increasingly recognized. These nonspecific responses may substantially benefit public health, but are also variable. In this issue of the JCI, Koeken and de Bree et al. report that BCG reduces circulating inflammatory markers in males but not in females, while de Bree and Mouritis et al. describe how diurnal rhythms affect the degree of BCG-induced innate memory. These studies further delineate factors that influence the magnitude of responses to BCG and may be crucial to harnessing its potential benefits.
Optimal population coding by noisy spiking neurons Tkačik, Gašper; Prentice, Jason S.; Balasubramanian, Vijay ...
Proceedings of the National Academy of Sciences - PNAS,
08/2010, Letnik:
107, Številka:
32
Journal Article
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In retina and in cortical slice the collective response of spiking neural populations is well described by "maximum-entropy" models in which only pairs of neurons interact. We asked, how should such ...interactions be organized to maximize the amount of information represented in population responses? To this end, we extended the linear-nonlinear-Poisson model of single neural response to include pairwise interactions, yielding a stimulus-dependent, pairwise maximum-entropy model. We found that as we varied the noise level in single neurons and the distribution of network inputs, the optimal pairwise interactions smoothly interpolated to achieve network functions that are usually regarded as discrete—stimulus decorrelation, error correction, and independent encoding. These functions reflected a trade-off between efficient consumption of finite neural bandwidth and the use of redundancy to mitigate noise. Spontaneous activity in the optimal network reflected stimulus-induced activity patterns, and single-neuron response variability overestimated network noise. Our analysis suggests that rather than having a single coding principle hardwired in their architecture, networks in the brain should adapt their function to changing noise and stimulus correlations.
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