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Supernovae and Gamma-Ray Bursts

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Abstract

Supernovae are explosions of stars which are triggered either by the implosion of the core of a star or a thermonuclear runaway, causing a bright optical display lasting for weeks to years. This chapter first explains the main explosion types, how they are classified, and the principles that determine their lightcurves. It then discusses in more detail some of the most important supernova types, specifically SN 1987A, the last naked-eye supernova near our own Galaxy, Type Ia supernovae that have been used as standardizable cosmological distance candles, and gamma-ray bursts and their related supernovae. Special emphasis is given to the link of the various supernova types to their progenitor systems and a discussion of any outstanding issues. Causes for the large diversity of supernova types and subtypes are then systematically explored: these include binarity, the explosion mechanisms, rotation, metallicity, and dynamical effects. Finally, some of the major topics of current interest are briefly discussed.

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Notes

  1. 1.

    Unlike supernovae that generally involve the whole star in the explosion, novae are now understood to be thermonuclear explosions in the envelopes of white dwarfs.

  2. 2.

    Traditionally, supernovae are named after the year and the order in the year in which the supernova was reported; therefore, SN 1987A was the first supernova that was reported in 1987. Today, with the discovery of hundreds of supernovae per year, not all supernovae are named based on this convention.

  3. 3.

    The Chandrasekhar limit defines the maximum mass at which a zero-temperature, self-gravitating object can be supported by electron degeneracty pressure. For typical white dwarf compositions, this mass is close to 1.4 M .

  4. 4.

    There are other ideas of how to generate a supernova explosion e.g., involving jet-driven explosions, or very strong magnetic fields. The latter also requires a very rapidly rotating pre-supernova core. While present pre-supernova models do not predict sufficiently rapidly rotating cores, there may be special circumstances in which this is the case, and this may be the origin of magnetars, neutron stars with very large magnetic fields, or even gamma-ray bursts (see Sect. 7.2).

  5. 5.

    It is presently not entirely clear how much He could be present in a SN Ic. Since He is non-thermally excited, it requires the presence of a source of energetic photons, e.g., from the radioactive decay of 56Ni. If the He layer is shielded from this radioactive source, it is possible in principle to hide significant amounts of He. However, the most recent estimates (Hachinger et al. 2012) suggest that at most, 0.2 M can be hidden.

  6. 6.

    The reason why this lightcurve does not show the initial peak seen for SN 1969L in Fig 14-3 is that Fig 14-3 shows a bolometric lightcurve, while Fig 14-4 shows a V -band lightcurve. The V -band lightcurve peaks later, as initially most of the radiation from the supernova escapes in the UV.

  7. 7.

    Even before the shock reaches the surface of the star, some radiation generated in the shocked region will diffuse outward faster than the shock front itself moves; when this radiation escapes from the progenitor, it produces a radiative precursor which precedes the actual shock breakout. Such a precursor has been observed for the II-P supernova SNLS-04D2dc (Schawinski et al. 2008).

  8. 8.

    Strictly speaking, there is no well-defined photosphere, as the point where the optical depth is of order unity is a strong function of wavelength.

  9. 9.

    Before the advent of BATSE, one of the few astrophysicists who strongly advocated a cosmological origin for GRBs was Bohdan Paczyński whose arguments at the time, however, were not taken very seriously by most people in the field.

  10. 10.

    BATSE has also detected many GRB-like events from the Earth’s atmosphere; these are associated with thunderstorms in the upper atmosphere. While they cannot be mistaken for classical GRBs because of their location, it is amusing that nature produces events that look very similar in terms of durations and observable gamma-ray fluxes but have very different underlying mechanisms on hugely varying energy scales.

  11. 11.

    NASA’s Swift satellite, launched in 2004, has only been able to detect clear jet breaks in a few GRBs, despite its much better sensitivity. It is presently not clear what implications this has for estimates of the jet opening angle and the beaming correction that needs to be applied.

  12. 12.

    The collapsar model is not the only model presently under consideration. One promising alternative involves the formation of a rapidly rotating neutron star with a very strong magnetic field, a magnetar, which is spun down on a timescale of a few seconds, extracting a large fraction of the rotational energy and powering a GRB (see, e.g., Metzger et al. 2011). Similar to the collapsar model, it requires a rapidly rotating progenitor core, but the final object is more likely a neutron star.

  13. 13.

    If a star experiences more than one mass-transfer phase, the nomenclature quickly becomes complicated, and there is no established standard notation.

  14. 14.

    Stable mass transfer can also occur for an expanding hydrogen-exhausted helium star (so-called case BB mass transfer). In this case, the star is likely to lose a large fraction/most of its helium envelope. This can produce a SN Ic progenitor with very low ejeta mass.

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© 2013 Springer Science+Business Media Dordrecht

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Podsiadlowski, P. (2013). Supernovae and Gamma-Ray Bursts. In: Oswalt, T.D., Barstow, M.A. (eds) Planets, Stars and Stellar Systems. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-5615-1_14

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