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TOPIC: Supernovae Ib and Ic

Blobrana

L

Posts: 131433

Date: Apr 12 11:33 2013

Type Ic Supernova	Permalink

Title: Super Luminous Ic Supernovae: catching a magnetar by the tail Authors: C. Inserra, S. J. Smartt, A. Jerkstrand, S. Valenti, M. Fraser, D. Wright, K. Smith, T.-W. Chen, R. Kotak, A. Pastorello, M. Nicholl, F. Bresolin, R. P. Kudritzki, S. Benetti, M. T. Botticella, W. S. Burgett, K. C. Chambers, M. Ergon, H. Flewelling, J. P. U. Fynbo, S. Geier, K. W. Hodapp, A. Howell, M. Huber, N. Keiser, G. Leloudas, L. Magill, E. A. Magnier, M. G. McCrumm, N. Metcalfe, P. A. Price, A. Rest, J. Sollerman, W. Sweeney, F. Taddia, S. Taubenberger, J. L. Tonry, R. J. Wainscoat, C. Waters, D. Young We report extensive observational data for five of the lowest redshift Super-Luminous Type Ic Supernovae (SL-SNe Ic) discovered to date. The five SNe, namely SN 2010md, SN 2011ke, SN 2011kg, SN 2011kf and SN 2012il show absolute peak magnitudes of -21.73\lesssim M_{g}(mag) \lesssim -20.42 and spectroscopic evolution similar to that of SN 2010gx. Photometric imaging of the transients at 50 to 230 days after peak combined with host galaxy subtraction reveals a luminous tail phase for four of these SL-SNe. A high resolution, optical and near infrared spectrum from xshooter provides detection of a broad He I \lambda 10830 emission line in the spectrum of SN 2012il at +50d after peak, revealing that at least some SL-SNe Ic are not completely helium free. At first sight, the tail luminosity decline rates that we measure are consistent with the radioactive decay of 56Co, and would require 1-4 \M of 56Ni to produce the luminosity. These quite large 56Ni masses cannot be made consistent with the short diffusion times at peak, and indeed are insufficient to power the peak luminosity. We instead favour energy deposition by newborn magnetars as the power source for these objects. A semi-analytical diffusion model with energy input from the spin-down of a magnetar reproduces the extensive lightcurve data well. The model predictions of ejecta velocities and temperatures which are required are in reasonable agreement with those determined from our photometric and spectroscopic observations. We derive magnetar energies of 0.4\lesssim E(10^{51}erg) \lesssim17 and ejecta masses of 2.3\lesssim M_{ej}(\M) \lesssim 9.7. The sample of five SL-SNe Ic presented here, combined with SN 2010gx - the best sampled SL-SNe Ic so far - point toward an explosion driven by a magnetar as a viable explanation for all SL-SNe Ic. Read more (1612kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: May 26 06:37 2012

Supernovae Ib and Ic	Permalink

Title: On the nature of supernovae Ib and Ic Authors: Luc Dessart, D. John Hillier, Chengdong Li, Stan Woosley Using non-LTE time-dependent radiative-transfer calculations, we study the impact of mixing and non-thermal processes associated with radioactive decay on SN IIb/Ib/Ic light curves (LCs) and spectra. Starting with short-period binary models of \leq5 solar mass He-rich stars (18-25 solar masses on the main-sequence), we produce 1.2B ejecta which we artificially mix to alter the chemical stratification. While the total 56Ni mass influences the LC peak, the spatial distribution of 56Ni, controlled by mixing processes, impacts both the multi-band LCs and spectra. With enhanced mixing, our synthetic LCs start their post-breakout re-brightening phase earlier, follow a more gradual rise to peak, appear redder, and fade faster after peak due to enhanced gamma-ray escape. Non-thermal electrons, crucial for the production of HeI lines, deposit a dominant fraction of their energy as heat. Because energy deposition is generally local well after the LC peak, the broad HeI lines characteristic of maximum-light SN IIb/Ib spectra require mixing that places 56Ni and helium nuclei to within a gamma-ray mean-free-path. This requirement indicates that SNe IIb and Ib most likely arise from the explosion of stripped-envelope massive stars (main-sequence masses \leq25 solar masses) that have evolved through mass-transfer in a binary system, rather than from more massive single WR stars. In contrast, the lack of HeI lines in SNe Ic may result from a variety of causes: A genuine helium deficiency; strongly-asymmetric mixing; weak mixing; or a more massive, perhaps single, progenitor characterised by a larger oxygen-rich core. Our models, subject to different mixing magnitudes, can produce a variety of SN types, including IIb, IIc, Ib, and Ic. As it is poorly constrained by explosion models, mixing challenges our ability to infer the progenitor and explosion properties of SNe IIb/Ib/Ic. Read more (638kb, PDF) __________________

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