5 research outputs found
Precursors prior to Type IIn supernova explosions are common: precursor rates, properties, and correlations
There is a growing number of supernovae (SNe), mainly of Type IIn, which
present an outburst prior to their presumably final explosion. These precursors
may affect the SN display, and are likely related to some poorly charted
phenomena in the final stages of stellar evolution. Here we present a sample of
16 SNe IIn for which we have Palomar Transient Factory (PTF) observations
obtained prior to the SN explosion. By coadding these images taken prior to the
explosion in time bins, we search for precursor events. We find five Type IIn
SNe that likely have at least one possible precursor event, three of which are
reported here for the first time. For each SN we calculate the control time.
Based on this analysis we find that precursor events among SNe IIn are common:
at the one-sided 99% confidence level, more than 50% of SNe IIn have at least
one pre-explosion outburst that is brighter than absolute magnitude -14, taking
place up to 1/3 yr prior to the SN explosion. The average rate of such
precursor events during the year prior to the SN explosion is likely larger
than one per year, and fainter precursors are possibly even more common. We
also find possible correlations between the integrated luminosity of the
precursor, and the SN total radiated energy, peak luminosity, and rise time.
These correlations are expected if the precursors are mass-ejection events, and
the early-time light curve of these SNe is powered by interaction of the SN
shock and ejecta with optically thick circumstellar material.Comment: 15 pages, 20 figures, submitted to Ap
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Visualization of Topological Boundary Modes Manifesting Topological Nodal-Point Superconductivity
The extension of the topological classification of band insulators to topological semimetals gave way to the topology classes of Dirac, Weyl, and nodal line semimetals with their unique Fermi arc and drum head boundary modes. Similarly, there are several suggestions to employ the classification of topological superconductors for topological nodal superconductors with Majorana boundary modes. Here, we show that the surface 1H termination of the transition metal dichalcogenide compound 4Hb-TaS2, in which 1T-TaS2 and 1H-TaS2 layers are interleaved, has the phenomenology of a topological nodal point superconductor. We find in scanning tunneling spectroscopy a residual density of states within the superconducting gap. An exponentially decaying bound mode is imaged within the superconducting gap along the boundaries of the exposed 1H layer characteristic of a gapless Majorana edge mode. The anisotropic nature of the localization length of the edge mode aims towards topological nodal superconductivity. A zero-bias conductance peak is further imaged within fairly isotropic vortex cores. All our observations are accommodated by a theoretical model of a two-dimensional nodal Weyl-like superconducting state, which ensues from inter-orbital Cooper pairing. The observation of an intrinsic topological nodal superconductivity in a layered material will pave the way for further studies of Majorana edge modes and its applications in quantum information processing.N.A., H.B., and B.Y acknowledge the German–Israeli Foundation for Scientific Research
and Development (GIF grant no. I-1364-303.7/2016). H.B. and N.A. acknowledge the
European Research Council (ERC, project no. TOPO NW), B.Y. acknowledges financial
support by the Willner Family Leadership Institute for the Weizmann Institute of Sci-
ence, the Benoziyo Endowment Fund for the Advancement of Science, the Ruth and Her-
man Albert Scholars Program for New Scientists, and the Israel Science Foundation (ISF
1251/19). G.A.F. gratefully acknowledges partial support from the National Science Foun-
dation through NSF Grant no. DMR-1720595, and DMR-1949701. Y.O. acknowledges
partial support through the ERC under the European Union’s Horizon 2020 research and
innovation programme (grant agreement LEGOTOP No 788715), the ISF Quantum Science
and Technology (2074/19), the BSF and NSF (2018643), and the CRC/Transregio 183. A.K.
acknowledges the Israel Science Foundation (ISF 320/17).Center for Dynamics and Control of Material