Type-Ia supernova rates and the progenitor problem, a review (1111.4492v2)

Abstract: The identity of the progenitor systems of type-Ia supernovae (SNe Ia) is a major unsolved problem in astrophysics. SN Ia rates are providing some striking clues. We review the basics of SN rate measurement, preach about some sins of SN rate measurement and analysis, and illustrate one of these sins with an analogy about Martian scientists. We review the recent progress in measuring SN Ia rates in various environments and redshifts, and their use to reconstruct the SN Ia delay time distribution (DTD) -- the SN rate versus time that would follow a hypothetical brief burst of star formation. A good number of DTD measurements, using a variety of methods, appear to be converging. At delays 1<t<10 Gyr, these measurements show a similar, ~t^-1, power-law shape. The DTD peaks at the shortest delays probed, although there is still some uncertainty regarding its precise shape at t<1 Gyr. At face value, this result supports the idea of a double-degenerate progenitor origin for SNe Ia. Single-degenerate progenitors may still play a role in producing short-delay SNe Ia, or perhaps all SNe Ia, if the red-giant donor channel is more efficient than found by most theoretical models. Apart from the DTD shape, the DTD normalization enjoys fairly good agreement (though perhaps some tension), among the various measurements, with a Hubble-time-integrated DTD value of about 2+/- 1 SNe Ia per 1000 Msun (stellar mass formed with a low-mass-turnover IMF). A recent attempt to characterize the local white dwarf binary population suggests that the white dwarf merger rate can explain the Galactic SN Ia rate, if sub-Chandra mergers lead to SN Ia events. We conclude by pointing to some future directions that should lead to progress in the field, including measurement of the bivariate (delay and stretch) SN Ia response function .

Type-Ia Supernova Rates and the Progenitor Problem

The paper "Type-Ia Supernova Rates and the Progenitor Problem" by Dan Maoz and Filippo Mannucci is a comprehensive review exploring the progenitor systems of Type-Ia supernovae (SNe Ia), a pivotal yet unresolved issue in astrophysics. The paper intricately discusses the methodologies for measuring supernova rates, addresses errors frequently made in such measurements, and synthesizes observational results with theoretical models to understand the delay time distribution (DTD) of SNe Ia.

Key Findings

1. Measurement of Supernova Rates: The authors highlight recent advancements in measuring SNe Ia rates across various environments and redshifts. A critical element in this measurement is the DTD, which indicates the supernova rate following a hypothetical burst of star formation.
2. Delay Time Distribution (DTD): Numerous methods show convergence towards a consistent picture of the DTD, which exhibits a power-law shape (~t^{-1}) for delays between 1 and 10 billion years (Gyr). This portrayal supports the double-degenerate (DD) progenitor model, where two white dwarfs (WDs) merge after losing energy through gravitational waves.
3. Implications for Progenitor Models: The DTD suggests that the single-degenerate (SD) model, which involves accretion from a non-degenerate companion star, might still contribute to short-delay SNe Ia. However, most evidence favors the DD scenario, potentially involving sub-Chandrasekhar-mass mergers that align with the observed rates.
4. Rate Normalization and Model Challenges: A Hubble-time-integrated DTD normalization estimates about 2±1 SNe Ia per 1000 $M_\odot$ of stellar mass formed. However, binary population synthesis models predict lower SN numbers than observed, pressing a need for theoretical recalibrations, such as including sub-Chandrasekhar systems.
5. Observational Discrepancies: Disparities remain between observed rate normalizations and theoretical predictions. The observed rates require 2.5% of local WDs to be SN Ia progenitors, a demand hard to meet by current models of super-Chandrasekhar mergers alone.

Theoretical and Observational Synthesis

The review meticulously synthesizes empirical data with theoretical projections. The evidence generally supports the DD model, highlighted by the power-law DTD extending to a Hubble time. Yet, potential contributions from the SD model, especially over short delays, are not entirely dismissed.

Moreover, the robustness of SN Ia understanding is in part limited by the variances in theoretical calculations which depend on numerous model parameters, e.g., the common-envelope phase, mass-loss rates, and the role of SD systems. This actuarial synthesis affirms observing population properties and measuring rates as critical lenses for confirming models.

Future Directions

The authors identify pivotal areas for further investigation, including the measurement of the bivariate SN Ia response function, which combines delay times with light curve stretch parameters. The prospect of sub-Chandra mergers as a photogenic explanation marks an exciting frontier needing experimental confirmation through localized observations and refined models.

Ongoing and future surveys, like those using advanced radio telescopes and multi-wavelength imaging, are expected to yield further insights into the mechanisms behind SN Ia progenitors. Such developments could also illuminate the broader cosmic implications of these astronomical phenomena.

Conclusion

This paper critically reviews the current understanding and remaining uncertainties in the astrophysical inquiry into SNe Ia progenitors. The authors argue cogently for the DD scenario, though not to the exclusion of other possibilities, urging continued integration of observational data with complex theoretical frameworks to solidify our understanding of these cosmologically significant events.