White dwarf dynamical interactions and fast optical transients

This is the author accepted manuscript. The final version is available from OUP via the DOI in this record.Recent advances in time-domain astronomy have uncovered a new class of optical transients with timescales shorter than typical supernovae and a wide range of peak luminosities. Several subtypes have been identi ed within this broad class, including Ca-rich transients, .Ia supernovae, and fast/bright transients. We examine the predic- tions from a state-of-the-art grid of three-dimensional simulations of dynamical white dwarf interactions in the context of these fast optical transients. We nd that for colli- sions involving carbon-oxygen or oxygen-neon white dwarfs the peak luminosities and durations of the light curves in our models are in good agreement with the properties of fast/bright transients. When one of the colliding white dwarfs is made of helium the properties of the light curves are similar to those of Ca-rich gap transients. The model lightcurves from our white dwarf collisions are too slow to reproduce those of .Ia SNe, and too fast to match any normal or peculiar Type Ia supernova.This work was partially funded by the MINECO grant AYA2014-59084-P and by the AGAUR (EG-B). CB acknowledges support from grants NASA ADAP NNX15AM03G S01 and NSF/AST-1412980. We acknowl- edge the useful comments of our referee, which helped in improving the original version of the paper

A white dwarf merger as progenitor of the anomalous X-ray pulsar 4U 0142+61?

It has been recently proposed that massive fast-rotating highly-magnetized white dwarfs could describe the observational properties of some of Soft Gamma-Ray Repeaters (SGRs) and Anomalous X-Ray Pulsars (AXPs). Moreover, it has also been shown that high-field magnetic (HFMWDs) can be the outcome of white dwarf binary mergers. The products of these mergers consist of a hot central white dwarf surrounded by a rapidly rotating disk. Here we show that the merger of a double degenerate system can explain the characteristics of the peculiar AXP 4U 0142+61. This scenario accounts for the observed infrared excess. We also show that the observed properties of 4U 0142+6 are consistent with an approximately 1.2 M_{\sun} white dwarf, remnant of the coalescence of an original system made of two white dwarfs of masses 0.6\, M_{\sun} and 1.0\, M_{\sun}. Finally, we infer a post-merging age $\tau_{\rm WD}\approx 64$ kyr, and a magnetic field $B\approx 2\times 10^8$ G. Evidence for such a magnetic field may come from the possible detection of the electron cyclotron absorption feature observed between the $B$ and $V$ bands at $\approx 10^{15}$ Hz in the spectrum of 4U 0142+61.Comment: to appear in ApJ Letter

One-armed spiral instability in double-degenerate post-merger accretion disks

This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.Increasing observational and theoretical evidence points to binary white dwarf mergers as the origin of some if not most normal Type Ia supernovae (SNe Ia). In this paper, we discuss the post-merger evolution of binary white dwarf (WD) mergers, and their relevance to the double-degenerate channel of SNe Ia. We present 3D simulations of carbon-oxygen (C/O) WD binary systems undergoing unstable mass transfer, varying both the total mass and the mass ratio. We demonstrate that these systems generally give rise to a one-armed gravitational spiral instability. The spiral density modes transport mass and angular momentum in the disk even in the absence of a magnetic field, and are most pronounced for secondary-to-primary mass ratios larger than 0.6. We further analyze carbon burning in these systems to assess the possibility of detonation. Unlike the case of a 1.1 + 1.0M C/O WD binary, we find that WD binary systems with lower mass and smaller mass ratios do not detonate as SNe Ia up to ∼ 8−22 outer dynamical times. Two additional models do however undergo net heating, and their secular increase in temperature could possibly result in a detonation on timescales longer than those considered hereWe thank James Guillochon, Daan Van Rossum, Chris Byrohl, and Pranav Dave for useful discussions. We also would like to thank the anonymous reviewer for their useful comments and insights. The work of EG-B, GA-S and PL-A was partially funded by MINECO AYA2014-59084-P grant and by the AGAUR. The software used in this work was in part developed by the DOE NNSA-ASC OASCR Flash Center at the University of Chicago. This work used the Extreme Science and Engineering discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Simulations at UMass Dartmouth were performed on a computer cluster supported by NSF grant CNS-0959382 and AFOSR DURIP grant FA9550-10-1-0354. RTF thanks the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the Kavli Institute for Theoretical Physics, supported in part by the national Science Foundation under grant NSF PHY11-25915, for visiting support during which this work was completed. This research has made use of resources from NASA’s Astrophysics Data System and the yt astrophysics analysis software suite (Turk et al. 2011)

Spiral instability can drive thermonuclear explosions in binary white dwarf mergers

This is the final version of the article. Available from American Astronomical Society via the DOI in this record.Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon–oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems that give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model that yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia.We thank James Guillochon, Lars Bildsten, Matthew Wise, and Gunnar Martin Lellep for useful discussions and Matthias Aegenheyster for his contributions to the FLASH analysis codes. E.G.B. acknowledges support from MCINN grant AYA2011–23102, and from the European Union FEDER fund. The software used in this work was in part developed by the DOE NNSA-ASC OASCR Flash Center at the University of Chicago. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1053575. Simulations at UMass Dartmouth were performed on a computer cluster supported by NSF grant CNS-0959382 and AFOSR DURIP grant FA9550-10-1-0354. This research has made use of NASA's Astrophysics Data System and the yt astrophysics analysis software suite Turk et al. (2011). R.T.F. is grateful to have had the opportunity to complete this paper during a visit to the Kavli Institute for Theoretical Physics, which is supported in part by the National Science Foundation under grant No. NSF PHY11-25915

White dwarf dynamical interactions and fast optical transients

Recent advances in time-domain astronomy have uncovered a new class of optical transients with timescales shorter than typical supernovae and a wide range of peak luminosities. Several subtypes have been identi ed within this broad class, including Ca-rich transients, .Ia supernovae, and fast/bright transients. We examine the predic- tions from a state-of-the-art grid of three-dimensional simulations of dynamical white dwarf interactions in the context of these fast optical transients. We nd that for colli- sions involving carbon-oxygen or oxygen-neon white dwarfs the peak luminosities and durations of the light curves in our models are in good agreement with the properties of fast/bright transients. When one of the colliding white dwarfs is made of helium the properties of the light curves are similar to those of Ca-rich gap transients. The model lightcurves from our white dwarf collisions are too slow to reproduce those of .Ia SNe, and too fast to match any normal or peculiar Type Ia supernova

Spiral instability can drive thermonuclear explosions in binary white dwarf mergers

Thermonuclear, or Type Ia supernovae (SNe Ia), originate from the explosion of carbon–oxygen white dwarfs, and serve as standardizable cosmological candles. However, despite their importance, the nature of the progenitor systems that give rise to SNe Ia has not been hitherto elucidated. Observational evidence favors the double-degenerate channel in which merging white dwarf binaries lead to SNe Ia. Furthermore, significant discrepancies exist between observations and theory, and to date, there has been no self-consistent merger model that yields a SNe Ia. Here we show that a spiral mode instability in the accretion disk formed during a binary white dwarf merger leads to a detonation on a dynamical timescale. This mechanism sheds light on how white dwarf mergers may frequently yield SNe Ia

One-armed spiral instability in double-degenerate post-merger accretion disks

Increasing observational and theoretical evidence points to binary white dwarf mergers as the origin of some if not most normal Type Ia supernovae (SNe Ia). In this paper, we discuss the post-merger evolution of binary white dwarf (WD) mergers, and their relevance to the double-degenerate channel of SNe Ia. We present 3D simulations of carbon-oxygen (C/O) WD binary systems undergoing unstable mass transfer, varying both the total mass and the mass ratio. We demonstrate that these systems generally give rise to a one-armed gravitational spiral instability. The spiral density modes transport mass and angular momentum in the disk even in the absence of a magnetic field, and are most pronounced for secondary-to-primary mass ratios larger than 0.6. We further analyze carbon burning in these systems to assess the possibility of detonation. Unlike the case of a 1.1 + 1.0M C/O WD binary, we find that WD binary systems with lower mass and smaller mass ratios do not detonate as SNe Ia up to ∼ 8−22 outer dynamical times. Two additional models do however undergo net heating, and their secular increase in temperature could possibly result in a detonation on timescales longer than those considered her