| 1. |
- De Marco, O., et al.
(författare)
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The messy death of a multiple star system and the resulting planetary nebula as observed by JWST
- 2022
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 6:12, s. 1421-1432
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Tidskriftsartikel (refereegranskat)abstract
- Planetary nebulae—the ejected envelopes of red giant stars—provide us with a history of the last, mass-losing phases of 90% of stars initially more massive than the Sun. Here we analyse images of the planetary nebula NGC 3132 from the James Webb Space Telescope (JWST) Early Release Observations. A structured, extended hydrogen halo surrounding an ionized central bubble is imprinted with spiral structures, probably shaped by a low-mass companion orbiting the central star at about 40–60 au. The images also reveal a mid-infrared excess at the central star, interpreted as a dusty disk, which is indicative of an interaction with another closer companion. Including the previously known A-type visual companion, the progenitor of the NGC 3132 planetary nebula must have been at least a stellar quartet. The JWST images allow us to generate a model of the illumination, ionization and hydrodynamics of the molecular halo, demonstrating the power of JWST to investigate complex stellar outflows. Furthermore, new measurements of the A-type visual companion allow us to derive the value for the mass of the progenitor of a central star with excellent precision: 2.86 ± 0.06 M⊙. These results serve as pathfinders for future JWST observations of planetary nebulae, providing unique insight into fundamental astrophysical processes including colliding winds and binary star interactions, with implications for supernovae and gravitational-wave systems.
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| 2. |
- Smartt, S. J., et al.
(författare)
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A kilonova as the electromagnetic counterpart to a gravitational-wave source
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7678, s. 75-
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Tidskriftsartikel (refereegranskat)abstract
- Gravitational waves were discovered with the detection of binary black-hole mergers(1) and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova(2-5). The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate(6). Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short.-ray burst(7,8). The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 +/- 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 +/- 0.1 times light speed. The power source is constrained to have a power-law slope of -1.2 +/- 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.
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| 3. |
- Pan, Y. -C, et al.
(författare)
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500 days of SN 2013dy : spectra and photometry from the ultraviolet to the infrared
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:4, s. 4307-4325
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Tidskriftsartikel (refereegranskat)abstract
- SN 2013dy is a Type Ia supernova (SN Ia) for which we have compiled an extraordinary data set spanning from 0.1 to similar to 500 d after explosion. We present 10 epochs of ultraviolet (UV) through near-infrared (NIR) spectra with Hubble Space Telescope/Space Telescope Imaging Spectrograph, 47 epochs of optical spectra (15 of them having high resolution), and more than 500 photometric observations in the BVrRiIZYJH bands. SN 2013dy has a broad and slowly declining light curve (Delta m(15)(B)= 0.92 mag), shallow Si II lambda 6355 absorption, and a low velocity gradient. We detect strong C II in our earliest spectra, probing unburned progenitor material in the outermost layers of the SN ejecta, but this feature fades within a few days. The UV continuum of SN 2013dy, which is strongly affected by the metal abundance of the progenitor star, suggests that SN 2013dy had a relatively high-metallicity progenitor. Examining one of the largest single set of high-resolution spectra for an SN Ia, we find no evidence of variable absorption from circumstellar material. Combining our UV spectra, NIR photometry, and high-cadence optical photometry, we construct a bolometric light curve, showing that SN 2013dy had a maximum luminosity of 10.0(-3.8)(+4.8) x 10(42) erg s(-1). We compare the synthetic light curves and spectra of several models to SN 2013dy, finding that SN 2013dy is in good agreement with a solar-metallicity W7 model.
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| 4. |
- Bulla, M., et al.
(författare)
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Predicting polarization signatures for double-detonation and delayed-detonation models of Type Ia supernovae
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462:1, s. 1039-1056
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of synthetic spectropolarimetry are one means to test multidimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M-circle dot white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a 2D double-detonation model and a 3D delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels (<1 per cent) for both explosion models. Polarization in the continuum peaks at similar to 0.1-0.3 per cent and decreases aftermaximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si II lambda 6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O I lambda 7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.
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| 5. |
- Bulla, M., et al.
(författare)
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Type Ia supernovae from violent mergers of carbon-oxygen white dwarfs : polarization signatures
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 455:1, s. 1060-1070
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Tidskriftsartikel (refereegranskat)abstract
- The violent merger of two carbon-oxygen white dwarfs has been proposed as a viable progenitor for some Type Ia supernovae. However, it has been argued that the strong ejecta asymmetries produced by this model might be inconsistent with the low degree of polarization typically observed in Type Ia supernova explosions. Here, we test this claim by carrying out a spectropolarimetric analysis for the model proposed by Pakmor et al. for an explosion triggered during the merger of a 1.1 and 0.9 M-circle dot carbon-oxygen white dwarf binary system. Owing to the asymmetries of the ejecta, the polarization signal varies significantly with viewing angle. We find that polarization levels for observers in the equatorial plane are modest (less than or similar to 1 per cent) and show clear evidence for a dominant axis, as a consequence of the ejecta symmetry about the orbital plane. In contrast, orientations out of the plane are associated with higher degrees of polarization and departures from a dominant axis. While the particular model studied here gives a good match to highly polarized events such as SN 2004dt, it has difficulties in reproducing the low polarization levels commonly observed in normal Type Ia supernovae. Specifically, we find that significant asymmetries in the element distribution result in a wealth of strong polarization features that are not observed in the majority of currently available spectropolarimetric data of Type Ia supernovae. Future studies will map out the parameter space of the merger scenario to investigate if alternative models can provide better agreement with observations.
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| 6. |
- Bulla, Mattia, et al.
(författare)
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White dwarf deflagrations for Type Iax supernovae : polarisation signatures from the explosion and companion interaction
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 635
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Tidskriftsartikel (refereegranskat)abstract
- Growing evidence suggests that Type Iax supernovae might be the result of thermonuclear deflagrations of Chandrasekhar-mass white dwarfs in binary systems. We carry out Monte Carlo radiative transfer simulations and predict spectropolarimetric features originating from the supernova explosion and subsequent ejecta interaction with the companion star. Specifically, we calculate viewing-angle dependent flux and polarisation spectra for a 3D model simulating the deflagration of a Chandrasekhar-mass white dwarf and, for a second model, simulating the ejecta interaction with a main-sequence star. We find that the intrinsic signal is weakly polarised and only mildly viewing-angle dependent, owing to the overall spherical symmetry of the explosion and the depolarising contribution of iron-group elements dominating the ejecta composition. The interaction with the companion star carves out a cavity in the ejecta and produces a detectable, but modest signal that is significant only at relatively blue wavelengths (less than or similar to 5000 angstrom). In particular, increasingly fainter and redder spectra are predicted for observer orientations further from the cavity, while a modest polarisation signal P similar to 0.2 per cent is found at blue wavelengths for orientations 30 degrees and 45 degrees away from the cavity. We find a reasonable agreement between the interaction model viewed from these orientations and spectropolarimetric data of SN 2005hk and interpret the maximum-light polarisation signal seen at blue wavelengths for this event as a possible signature of the ejecta-companion interaction. We encourage further polarimetric observations of SNe Iax to test whether our results can be extended and generalised to the whole SN Iax class.
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| 7. |
- Chen, T.-W., et al.
(författare)
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SN 2017ens : The Metamorphosis of a Luminous Broadlined Type Ic Supernova into an SN IIn
- 2018
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 867:2
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of supernova (SN) 2017ens, discovered by the ATLAS survey and identified as a hot blue object through the GREAT program. The redshift z = 0.1086 implies a peak brightness of M-g = -21.1 mag, placing the object within the regime of superluminous supernovae. We observe a dramatic spectral evolution, from initially being blue and featureless, to later developing features similar to those of the broadlined Type Ic SN 1998bw, and finally showing 2000 km s(-1) wide H alpha and H beta emission. Relatively narrow Balmer emission (reminiscent of a SN IIn) is present at all times. We also detect coronal lines, indicative of a dense circumstellar medium. We constrain the progenitor wind velocity to similar to 50-60 km s(-1) based on P-Cygni profiles, which is far slower than those present in Wolf-Rayet stars. This may suggest that the progenitor passed through a luminous blue variable phase, or that the wind is instead from a binary companion red supergiant star. At late times we see the similar to 2000 km s(-1) wide H alpha emission persisting at high luminosity (similar to 3 x 10(40) erg s(-1)) for at least 100 day, perhaps indicative of additional mass loss at high velocities that could have been ejected by a pulsational pair instability.
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| 8. |
- Childress, M. J., et al.
(författare)
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Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 454:4, s. 3816-3842
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Tidskriftsartikel (refereegranskat)abstract
- The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of Ni-56 to Co-56 at early times, and the decay of Co-56 to Fe-56 from similar to 60 d after explosion. We examine the evolution of the [Co III] lambda 5893 emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of Co-56 as a function of time. This result indicates both efficient local energy deposition from positrons produced in Co-56 decay and long-term stability of the ionization state of the nebula. We compile SN Ia nebular spectra from the literature and present 21 new late-phase spectra of 7 SNe Ia, including SN 2014J. From these we measure the flux in the [Co III] lambda 5893 line and remove its well-behaved time dependence to infer the initial mass of Ni-56 (M-Ni, produced in the explosion. We then examine Ni-56 yields for different SN Ia ejected masses (M-ej-calculated using the relation between light-curve width and ejected mass) and find that the Ni-56 masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s similar to 0.7-0.9), M-Ni is clustered near MN, 0.4 Me and shows a shallow increase as Mei increases from similar to 1 to 1.4 M-circle dot; at high stretch, M-ej clusters at the Chandrasekhar mass (1.4 M-circle dot) while M-Ni, spans a broad range from 0.6 to 1.2 M-circle dot. This could constitute evidence for two distinct SN Ia explosion mechanisms.
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| 9. |
- Foley, Ryan J., et al.
(författare)
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Extensive HST ultraviolet spectra and multiwavelength observations of SN 2014J in M82 indicate reddening and circumstellar scattering by typical dust
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 443:4, s. 2887-2906
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Tidskriftsartikel (refereegranskat)abstract
- SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least 28 yr and perhaps in 410 yr. Despite its small distance of 3.3 Mpc, SN 2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN Ia luminosity, we infer an observed visual extinction of A(V) = 2.0 +/- 0.1 mag. But this picture, with R-V = 1.6 +/- 0.2, is too simple to account for all observations. We combine 10 epochs (spanning a month) of HST/Space Telescope Imaging Spectrograph (STIS) ultraviolet through near-infrared spectroscopy with HST/Wide Field Camera 3 (WFC3), Katzman Automatic Imaging Telescope, and FanCam photometry from the optical to the infrared and nine epochs of high-resolution TRES (Tillinghast Reflection Echelle Spectrograph) spectroscopy to investigate the sources of extinction and reddening for SN 2014J. We argue that the wide range of observed properties for SN 2014J is caused by a combination of dust reddening, likely originating in the interstellar medium of M82, and scattering off circumstellar material. For this model, roughly half of the extinction is caused by reddening from typical dust (E(B - V) = 0.45 mag and R-V = 2.6) and roughly half by scattering off Large Magellanic Cloud-like dust in the circumstellar environment of SN 2014J.
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| 10. |
- Foley, Ryan J., et al.
(författare)
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THE FIRST MAXIMUM-LIGHT ULTRAVIOLET THROUGH NEAR-INFRARED SPECTRUM OF A TYPE Ia SUPERNOVA
- 2012
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Ingår i: THE ASTROPHYSICAL JOURNAL LETTERS. - 2041-8205. ; 753:1, s. L5-
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Tidskriftsartikel (refereegranskat)abstract
- We present the first maximum-light ultraviolet (UV) through near-infrared (NIR) Type Ia supernova (SN Ia) spectrum. This spectrum of SN 2011iv was obtained nearly simultaneously by the Hubble Space Telescope at UV/optical wavelengths and the Magellan Baade telescope at NIR wavelengths. These data provide the opportunity to examine the entire maximum-light SN Ia spectral energy distribution. Since the UV region of an SN Ia spectrum is extremely sensitive to the composition of the outer layers of the explosion, which are transparent at longer wavelengths, this unprecedented spectrum can provide strong constraints on the composition of the SN ejecta, and similarly the SN explosion and progenitor system. SN 2011iv is spectroscopically normal, but has a relatively fast decline (Delta m(15)(B) = 1.69 +/- 0.05 mag). We compare SN 2011iv to other SNe Ia with UV spectra near maximum light and examine trends between UV spectral properties, light-curve shape, and ejecta velocity. We tentatively find that SNe with similar light-curve shapes but different ejecta velocities have similar UV spectra, while those with similar ejecta velocities but different light-curve shapes have very different UV spectra. Through a comparison with explosion models, we find that both a solar-metallicity W7 and a zero-metallicity delayed-detonation model provide a reasonable fit to the spectrum of SN 2011iv from the UV to the NIR.
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| 11. |
- Kerzendorf, W. E., et al.
(författare)
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Extremely late photometry of the nearby SN 2011fe
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 472:3, s. 2534-2542
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Tidskriftsartikel (refereegranskat)abstract
- Type Ia supernovae are widely accepted to be the outcomes of thermonuclear explosions in white dwarf stars. However, many details of these explosions remain uncertain (e.g. the mass, ignition mechanism and flame speed). Theory predicts that at very late times (beyond 1000 d) it might be possible to distinguish between explosion models. Few very nearby supernovae can be observed that long after the explosion. The Type Ia supernova SN 2011fe located in M101 and along a line of sight with negligible extinction, provides us with the once-in-a-lifetime chance to obtain measurements that may distinguish between theoretical models. In this work, we present the analysis of photometric data of SN2011fe taken between 900 and 1600 d after explosion with Gemini and HST. At these extremely late epochs theory suggests that the light-curve shape might be used to measure isotopic abundances which is a useful model discriminant. However, we show in this work that there are several currently not well constrained physical processes introducing large systematic uncertainties to the isotopic abundance measurement. We conclude that without further detailed knowledge of the physical processes at this late stage one cannot reliably exclude any models on the basis of this data set.
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| 12. |
- Kromer, Markus, et al.
(författare)
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Deflagrations in hybrid CONe white dwarfs : a route to explain the faint Type Iax supernova 2008ha
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 450:3, s. 3045-3053
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Tidskriftsartikel (refereegranskat)abstract
- Stellar evolution models predict the existence of hybrid white dwarfs (WDs) with a carbon-oxygen core surrounded by an oxygen-neon mantle. Being born with masses similar to 1.1 M-aS (TM), hybrid WDs in a binary system may easily approach the Chandrasekhar mass (M-Ch) by accretion and give rise to a thermonuclear explosion. Here, we investigate an off-centre deflagration in a near-M-Ch hybrid WD under the assumption that nuclear burning only occurs in carbon-rich material. Performing hydrodynamics simulations of the explosion and detailed nucleosynthesis post-processing calculations, we find that only 0.014 M-aS (TM) of material is ejected while the remainder of the mass stays bound. The ejecta consist predominantly of iron-group elements, O, C, Si and S. We also calculate synthetic observables for our model and find reasonable agreement with the faint Type Iax SN 2008ha. This shows for the first time that deflagrations in near-M-Ch WDs can in principle explain the observed diversity of Type Iax supernovae. Leaving behind a near-M-Ch bound remnant opens the possibility for recurrent explosions or a subsequent accretion-induced collapse in faint Type Iax SNe, if further accretion episodes occur. From binary population synthesis calculations, we find the rate of hybrid WDs approaching M-Ch to be of the order of 1 per cent of the Galactic SN Ia rate.
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| 13. |
- Kromer, Markus, et al.
(författare)
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SN 2010LP-A TYPE IA SUPERNOVA FROM A VIOLENT MERGER OF TWO CARBON-OXYGEN WHITE DWARFS
- 2013
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 778:1
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Tidskriftsartikel (refereegranskat)abstract
- SN 2010lp is a subluminous Type Ia supernova (SN Ia) with slowly evolving lightcurves. Moreover, it is the only subluminous SN Ia observed so far that shows narrow emission lines of [O I] in late-time spectra, indicating unburned oxygen close to the center of the ejecta. Most explosion models for SNe Ia cannot explain the narrow [O I] emission. Here, we present hydrodynamic explosion and radiative transfer calculations showing that the violent merger of two carbon-oxygen white dwarfs of 0.9 and 0.76 M-circle dot adequately reproduces the early-time observables of SN 2010lp. Moreover, our model predicts oxygen close to the center of the explosion ejecta, a pre-requisite for narrow [O I] emission in nebular spectra as observed in SN 2010lp.
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| 14. |
- Kromer, Markus, et al.
(författare)
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The peculiar Type Ia supernova iPTF14atg : Chandrasekhar-mass explosion or violent merger?
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 459:4, s. 4428-4439
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Tidskriftsartikel (refereegranskat)abstract
- iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system, where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multidimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 M-aS (TM), respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10 d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circumstellar medium and surface radioactivity from an He-ignited merger that may be able to account for the early UV emission in violent merger models.
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| 15. |
- Magee, M. R., et al.
(författare)
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The type Iax supernova, SN 2015H A white dwarf deflagration candidate
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 589
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Tidskriftsartikel (refereegranskat)abstract
- We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M-r = 17.27 +/- 0.07, and a (Delta m(15))(r) = 0.69 +/- 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of similar to 0.2 M-circle dot of material containing similar to 0.07 M-circle dot of Ni-56. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that less than or similar to 0.6 M-circle dot of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.
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| 16. |
- Sasdelli, Michele, et al.
(författare)
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A metric space for Type Ia supernova spectra : a new method to assess explosion scenarios
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 466:4, s. 3784-3809
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Tidskriftsartikel (refereegranskat)abstract
- Over the past years, Type Ia supernovae (SNe Ia) have become a major tool to determine the expansion history of the Universe, and considerable attention has been given to, both, observations and models of these events. However, until now, their progenitors are not known. The observed diversity of light curves and spectra seems to point at different progenitor channels and explosion mechanisms. Here, we present a newway to compare model predictions with observations in a systematic way. Our method is based on the construction of a metric space for SN Ia spectra by means of linear principal component analysis, taking care of missing and/or noisy data, and making use of partial least-squares regression to find correlations between spectral properties and photometric data. We investigate realizations of the three major classes of explosion models that are presently discussed: delayed-detonation Chandrasekharmass explosions, sub-Chandrasekhar-mass detonations and double-degenerate mergers, and compare them with data. We show that in the principal component space, all scenarios have observed counterparts, supporting the idea that different progenitors are likely. However, all classes of models face problems in reproducing the observed correlations between spectral properties and light curves and colours. Possible reasons are briefly discussed.
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| 17. |
- Seitenzahl, I. R., et al.
(författare)
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5.9-keV Mn K-shell X-ray luminosity from the decay of Fe-55 in Type Ia supernova models
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 447:2, s. 1484-1490
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Tidskriftsartikel (refereegranskat)abstract
- We show that the X-ray line flux of the Mn Ka line at 5.9 keV from the decay of Fe-55 is a promising diagnostic to distinguish between Type Ia supernova (SN Ia) explosion models. Using radiation transport calculations, we compute the line flux for two three-dimensional explosion models: a near-Chandrasekhar mass delayed detonation and a violent merger of two (1.1 and 0.9 M-circle dot) white dwarfs. Both models are based on solar metallicity zero-age main-sequence progenitors. Due to explosive nuclear burning at higher density, the delayed-detonation model synthesizes similar to 3.5 times more radioactive Fe-55 than the merger model. As a result, we find that the peak Mn K alpha line flux of the delayed-detonation model exceeds that of the merger model by a factor of similar to 4.5. Since in both models the 5.9-keV X-ray flux peaks five to six years after the explosion, a single measurement of the X-ray line emission at this time can place a constraint on the explosion physics that is complementary to those derived from earlier phase optical spectra or light curves. We perform detector simulations of current and future X-ray telescopes to investigate the possibilities of detecting the X-ray line at 5.9 keV. Of the currently existing telescopes, XMM-Newton/pn is the best instrument for close (less than or similar to 1-2 Mpc), non-background limited SNe Ia because of its large effective area. Due to its low instrumental background, Chandra/ACIS is currently the best choice for SNe Ia at distances above similar to 2 Mpc. For the delayed-detonation scenario, a line detection is feasible with Chandra up to similar to 3 Mpc for an exposure time of 10(6) s. We find that it should be possible with currently existing X-ray instruments (with exposure times less than or similar to 5 x 10(5) s) to detect both of our models at sufficiently high S/N to distinguish between them for hypothetical events within the Local Group. The prospects for detection will be better with future missions. For example, the proposed Athena/X-IFU instrument could detect our delayed-detonation model out to a distance of similar to 5 Mpc. This would make it possible to study future events occurring during its operational life at distances comparable to those of the recent supernovae SN 2011 fe (similar to 6.4 Mpc) and SN 2014J (similar to 3.5 Mpc).
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| 18. |
- Shingles, L. J., et al.
(författare)
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Monte Carlo radiative transfer for the nebular phase of Type Ia supernovae
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 492:2, s. 2029-2043
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Tidskriftsartikel (refereegranskat)abstract
- We extend the range of validity of the ARTIS 3D radiative transfer code up to hundreds of days after explosion, when Type Ia supernovae (SNe Ia) are in their nebular phase. To achieve this, we add a non-local thermodynamic equilibrium population and ionization solver, a new multifrequency radiation field model, and a new atomic data set with forbidden transitions. We treat collisions with non-thermal leptons resulting from nuclear decays to account for their contribution to excitation, ionization, and heating. We validate our method with a variety of tests including comparing our synthetic nebular spectra for the well-known one-dimensional W7 model with the results of other studies. As an illustrative application of the code, we present synthetic nebular spectra for the detonation of a sub-Chandrasekhar white dwarf (WD) in which the possible effects of gravitational settling of Ne-22 prior to explosion have been explored. Specifically, we compare synthetic nebular spectra for a 1.06 M-circle dot WD model obtained when 5.5 Gyr of very efficient settling is assumed to a similar model without settling. We find that this degree of Ne-22 settling has only amodest effect on the resulting nebular spectra due to increased Ni-58 abundance. Due to the high ionization in sub-Chandrasekhar models, the nebular [Ni II] emission remains negligible, while the [Ni III] line strengths are increased and the overall ionization balance is slightly lowered in the model with Ne-22 settling. In common with previous studies of sub-Chandrasekhar models at nebular epochs, these models overproduce [Fe III] emission relative to [Fe II] in comparison to observations of normal SNe Ia.
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| 19. |
- Taubenberger, S., et al.
(författare)
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Spectroscopy of the Type Ia supernova 2011fe past 1000 d
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 448:1, s. L48-L52
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Tidskriftsartikel (refereegranskat)abstract
- In this Letter we present an optical spectrum of SN 2011fe taken 1034 d after the explosion, several hundred days later than any other spectrum of a Type Ia supernova (disregarding light-echo spectra and Local Group remnants). The spectrum is still dominated by broad emission features, with no trace of a light echo or interaction of the supernova ejecta with surrounding interstellar material. Comparing this extremely late spectrum to an earlier one taken 331 d after the explosion, we find that the most prominent feature at 331 d - [Fe III] emission around 4700 angstrom - has entirely faded away, suggesting a significant change in the ionization state. Instead, [Fe II] lines are probably responsible for most of the emission at 1034 d. An emission feature at 6300-6400 angstrom has newly developed at 1034 d, which we tentatively identify with Fe I lambda 6359, [Fe I] lambda lambda 6231, 6394 or [O I] lambda lambda 6300, 6364. Interestingly, the features in the 1034 d spectrum seem to be collectively redshifted, a phenomenon that we currently have no convincing explanation for. We discuss the implications of our findings for explosion models, but conclude that sophisticated spectral modelling is required for any firm statement.
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| 20. |
- Yuan, Fang, et al.
(författare)
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450 d of Type II SN 2013ej in optical and near-infrared
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 461:2, s. 2003-2018
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Tidskriftsartikel (refereegranskat)abstract
- We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 d after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M-V =-17.6) but a small 56Ni production of similar to 0.023 M-circle dot. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the H a profile typical for a Type IIL. During transition to the radioactive decay tail at similar to 100 d, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from Co-56 decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M-ZAMS = 12-15 M-circle dot progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.
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