| 1. |
- Bobrick, Alexey, et al.
(författare)
-
Transients from ONe white dwarf - neutron star/black hole mergers
- 2022
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 510:3, s. 3758-3777
-
Tidskriftsartikel (refereegranskat)abstract
- We conduct the first 3D hydrodynamic simulations of oxygen-neon white dwarf-neutron star/black hole mergers (ONe WD-NS/BH mergers). Such mergers constitute a significant fraction, and may even dominate, the inspiral rates of all WD-NS binaries. We post-process our simulations to obtain the nuclear evolution of these systems and couple the results to a supernova spectral synthesis code to obtain the first light curves and spectra for these transients. We find that the amount of 56Ni synthesized in these mergers grows as a strong function of the WD mass, reaching typically 0.05 and up to 0.1M⊙ per merger. Photodisintegration leads to similar amounts of 4He and about a ten times smaller amount of 1H. The nuclear yields from these mergers, in particular those of 55Mn, may contribute significantly to Galactic chemical evolution. The transients expected from ONe WD-NS mergers are dominantly red/infrared, evolve on month-long time-scales and reach bolometric magnitudes of up to -16.5. The current surveys must have already detected these transients or are, alternatively, putting strong constraints on merger scenarios. The properties of the expected transients from WD-NS mergers best agree with faint type Iax supernovae. The Vera Rubin Observatory (LSST) will be detecting up to thousands of merging ONe WD-NS systems per year. We simulate a subset of our models with 2D axisymmetric FLASH code to investigate why they have been challenging for previous studies. We find that the likely main challenge has been effectively modelling the nuclear statistical equilibrium regime in such mergers.
|
|
| 2. |
- Grishin, Evgeni, et al.
(författare)
-
Supernova explosions in active galactic nuclear discs
- 2021
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 507:1, s. 156-174
-
Tidskriftsartikel (refereegranskat)abstract
- Active galactic nuclei (AGNs) are prominent environments for stellar capture, growth, and formation. These environments may catalyse stellar mergers and explosive transients, such as thermonuclear and core-collapse supernovae (SNe). SN explosions in AGN discs generate strong shocks, leading to unique observable signatures. We develop an analytical model that follows the evolution of the shock propagating in the disc until it eventually breaks out. We derive the peak luminosity, bolometric light curve, and breakout time. The peak luminosities may exceed 1045 erg s−1 and last from hours to days. The brightest explosions occur in regions of reduced density: either off-plane, or in discs around low-mass central black holes (∼106 M⊙), or in starved subluminous AGNs. Explosions in the latter two sites are easier to observe due to a reduced AGN background luminosity. We perform suites of 1D Lagrangian radiative hydrodynamics snec code simulations to validate our results and obtain the luminosity in different bands, and 2D axisymmetric Eulerian hydrodynamics code hormone simulations to study the morphology of the ejecta and its deviation from spherical symmetry. The observed signature is expected to be a bright blue, UV or X-ray flare on top of the AGN luminosity from the initial shock breakout, while the subsequent red part of the light curve will largely be unobservable. We estimate the upper limit for the total event rate to be R≲100 yr−1 Gpc−3 for optimal conditions and discuss the large uncertainties in this estimate. Future high-cadence transient searches may reveal these events. Some existing tidal disruption event candidates may originate from AGN SNe.
|
|
| 3. |
|
|
| 4. |
- Jacobson-Galán, Wynn V., et al.
(författare)
-
Late-time Observations of Calcium-rich Transient SN 2019ehk Reveal a Pure Radioactive Decay Power Source
- 2021
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 908:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present multiband Hubble Space Telescope imaging of the calcium-rich supernova (SN) SN 2019ehk at 276-389 days after explosion. These observations represent the latest B-band to near-IR photometric measurements of a calcium-rich transient to date and allow for the first opportunity to analyze the late-time bolometric evolution of an object in this observational SN class. We find that the late-time bolometric light curve of SN 2019ehk can be described predominantly through the radioactive decay of 56Co for which we derive a mass of M(56Co) = (2.8 ± 0.1) × 10-2 M o. Furthermore, the rate of decline in bolometric luminosity requires the leakage of γ-rays on timescale t γ = 53.9 ± 1.30 days, but we find no statistical evidence for incomplete positron trapping in the SN ejecta. While our observations cannot constrain the exact masses of other radioactive isotopes synthesized in SN 2019ehk, we estimate a mass ratio limit of M(57Co)/M(56Co) ≤ 0.030. This limit is consistent with the explosive nucleosynthesis produced in the merger of low-mass white dwarfs, which is one of the favored progenitor scenarios in early-time studies of SN 2019ehk.
|
|
| 5. |
- Roy, Niranjan C., et al.
(författare)
-
3D Hydrodynamical Simulations of Helium-ignited Double-degenerate White Dwarf Mergers
- 2022
-
Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 932:2
-
Tidskriftsartikel (refereegranskat)abstract
- The origins of Type Ia supernovae (SNe Ia) are still debated. Some of the leading scenarios involve a double detonation in double white dwarf (WD) systems. In these scenarios, helium shell detonation occurs on top of a carbon-oxygen (CO) WD, which then drives the detonation of the CO core, producing an SN Ia. Extensive studies have been done on the possibility of a double helium detonation, following a dynamical helium mass-transfer phase onto a CO-WD. However, 3D self-consistent modeling of the double-WD system, the mass transfer, and the helium shell detonation have been little studied. Here we use 3D hydrodynamical simulations to explore this case in which a helium detonation occurs near the point of Roche lobe overflow of the donor WD and may lead to an SN Ia through the dynamically driven double-degenerate double-detonation (D6) mechanism. We find that the helium layer of the accreting primary WD does undergo a detonation, while the underlying CO core does not, leading to an extremely rapid and faint nova-like transient instead of a luminous SN Ia event. This failed core detonation suggests that D6 SNe Ia may be restricted to the most massive CO primary WDs. We highlight the nucleosynthesis of the long-lived radioisotope 44Ti during explosive helium burning, which may serve as a hallmark both of successful as well as failed D6 events, which subsequently detonate as classical double-degenerate mergers.
|
|
| 6. |
- Waldman, Roni, et al.
(författare)
-
HELIUM SHELL DETONATIONS ON LOW-MASS WHITE DWARFS AS A POSSIBLE EXPLANATION FOR SN 2005E
- 2011
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 738:1, s. 21-
-
Tidskriftsartikel (refereegranskat)abstract
- Recently, several Type Ib supernovae (SNe; with the prototypical SN 2005E) have been shown to have atypical properties. These SNe are faint (absolute peak magnitude of similar to-15) and fast SNe that show unique composition. They are inferred to have low ejecta mass (a few tenths of a solar mass) and to be highly enriched in calcium, but poor in silicon elements and nickel. These SNe were therefore suggested to belong to a new class of calcium-rich faint SNe explosions. Their properties were proposed to be the result of helium detonations that may occur on helium accreting white dwarfs. In this paper, we theoretically study the scenario of helium detonations and focus on the results of detonations in accreted helium layers on low-mass carbon-oxygen (CO) cores. We present new results from one-dimensional simulations of such explosions, including their light curves and spectra. We find that when the density of the helium layer is low enough the helium detonation produces large amounts of intermediate elements, such as calcium and titanium, together with a large amount of unburnt helium. Alternatively, enough carbon enrichment of the accreted helium as a result of convective undershoot at the early stages of the runaway can avoid the production of iron group elements as the alpha particles are consumed avoiding iron production. Our results suggest that the properties of calcium-rich faint SNe could indeed be consistent with the helium-detonation scenario on small CO cores. Above a certain density (larger CO cores) the detonation leaves mainly (56)Ni and unburnt helium, and the predicted spectrum will unlikely fit the unique features of this class of SNe. Finally, none of our studied models reproduces the bright, fast-evolving light curves of another type of peculiar SNe suggested to originate in helium detonations (SNe 1885A, 1939B, and 2002bj).
|
|
| 7. |
- Zenati, Yossef, et al.
(författare)
-
Faint Rapid Red Transients from Neutron Star - CO White Dwarf Mergers
- 2020
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 1365-2966 .- 0035-8711. ; 493:3, s. 3956-3965
-
Tidskriftsartikel (refereegranskat)abstract
- Mergers of neutron stars (NS) and white dwarfs (WD) may give rise to observable explosive transientevents. We use 3D hydrodynamical (SPH) simulations, as well as 2D hydrodynamical-thermonuclearsimulations (using the FLASH AMR code) to model the disruption of CO-WDs by NSs, whichproduce faint transient events. We post-process the simulations using a large nuclear network andmake use of the SuperNu radiation-transfer code to predict the observational signatures and detailedproperties of these transients. We calculate the light-curves (LC) and spectra for five models of NS -CO-WD mergers. The small yields of56Ni (few×10−3M) result in faint, rapidly-evolving reddenedtransients (RRTs) with B (R) - peak magnitudes of at most∼−12 (−13) to∼−13 (−15), muchshorter and fainter than both regular and faint/peculiar type-Ia SNe. These transients are likely to beaccompanied by several months-long, 1–2 mag dimmer red/IR afterglows. We show that the spectraof RRTs share some similarities with rapidly-evolving transients such as SN2010x, although RRTsare significantly fainter, especially in the I/R bands, and show far stronger Si lines. We estimate thatthe upcoming Large Synoptic Survey Telescope could detect RRTs at a rate of up to∼10−70 yr−1,through observations in the R/I bands. The qualitative agreement between the SPH and FLASHapproaches supports the earlier hydrodynamical studies of these systems.
|
|
