| 1. |
- Alp, Dennis, et al.
(författare)
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The 30 Year Search for the Compact Object in SN 1987A
- 2018
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Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 864:2
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Tidskriftsartikel (refereegranskat)abstract
- Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.
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| 2. |
- Clocchiatti, Alejandro, et al.
(författare)
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Late-time HST photometry of SN1994I : Hints of positron annihilation energy deposition
- 2008
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 120:865, s. 290-300
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Tidskriftsartikel (refereegranskat)abstract
- We present multicolor Hubble Space Telescope ( HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained similar to 280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the gamma-rays produced by the radioactive decay of Co-56 diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.
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| 3. |
- Davis, Tamara, et al.
(författare)
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Scrutinizing Exotic Cosmological Models Using ESSENCE Supernova Data Combined with Other Cosmological Probes
- 2007
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Ingår i: The Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 666:2, s. 716-725
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Tidskriftsartikel (refereegranskat)abstract
- The first cosmological results from the ESSENCE supernova survey (Wood-Vasey and coworkers) are extended to a wider range of cosmological models including dynamical dark energy and nonstandard cosmological models. We fold in a greater number of external data sets such as the recent Higher-z release of high-redshift supernovae (Riess and coworkers), as well as several complementary cosmological probes. Model comparison statistics such as the Bayesian and Akaike information criteria are applied to gauge the worth of models. These statistics favor models that give a good fit with fewer parameters. Based on this analysis, the preferred cosmological model is the flat cosmological constant model, where the expansion history of the universe can be adequately described with only one free parameter describing the energy content of the universe. Among the more exotic models that provide good fits to the data, we note a preference for models whose best-fit parameters reduce them to the cosmological constant model.
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| 4. |
- Dhawan, Suhail, et al.
(författare)
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Measuring the Hubble constant with Type Ia supernovae as near-infrared standard candles
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 609
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Tidskriftsartikel (refereegranskat)abstract
- The most precise local measurements of H-0 rely on observations of Type Ia supernovae (SNe Ia) coupled with Cepheid distances to SN Ia host galaxies. Recent results have shown tension comparing H-0 to the value inferred from CMB observations assuming Lambda CDM, making it important to check for potential systematic uncertainties in either approach. To date, precise local H-0 measurements have used SN Ia distances based on optical photometry, with corrections for light curve shape and colour. Here, we analyse SNe Ia as standard candles in the near-infrared (NIR), where luminosity variations in the supernovae and extinction by dust are both reduced relative to the optical. From a combined fit to 9 nearby calibrator SNe with host Cepheid distances from Riess et al. (2016) and 27 SNe in the Hubble flow, we estimate the absolute peak J magnitude M-J = -18.524 +/- 0.041 mag and H-0 = 72.8 +/- 1.6 (statistical) +/- 2.7 (systematic) km s(-1) Mpc(-1). The 2.2% statistical uncertainty demonstrates that the NIR provides a compelling avenue to measuring SN Ia distances, and for our sample the intrinsic (unmodeled) peak J magnitude scatter is just similar to 0.10 mag, even without light curve shape or colour corrections. Our results do not vary significantly with different sample selection criteria, though photometric calibration in the NIR may be a dominant systematic uncertainty. Our findings suggest that tension in the competing H-0 distance ladders is likely not a result of supernova systematics that could be expected to vary between optical and NIR wavelengths, like dust extinction. We anticipate further improvements in H-0 with a larger calibrator sample of SNe Ia with Cepheid distances, more Hubble flow SNe Ia with NIR light curves, and better use of the full NIR photometric data set beyond simply the peak J-band magnitude.
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| 5. |
- Diehl, Roland, et al.
(författare)
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Cosmic nucleosynthesis : A multi-messenger challenge
- 2022
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Ingår i: Progress in Particle and Nuclear Physics. - : Elsevier. - 0146-6410 .- 1873-2224. ; 127
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Forskningsöversikt (refereegranskat)abstract
- The origins of the elements and isotopes of cosmic material is a critical aspect of understanding the evolution of the universe. Nucleosynthesis typically requires physical conditions of high temperatures and densities. These are found in the Big Bang, in the interiors of stars, and in explosions with their compressional shocks and high neutrino and neutron fluxes. Many different tools are available to disentangle the composition of cosmic matter, in material of extraterrestrial origins such as cosmic rays, meteorites, stardust grains, lunar and terrestrial sediments, and through astronomical observations across the electromagnetic spectrum. Understanding cosmic abundances and their evolution requires combining such measurements with approaches of astrophysical, nuclear theories and laboratory experiments, and exploiting additional cosmic messengers, such as neutrinos and gravitational waves. Recent years have seen significant progress in almost all these fields; they are presented in this review. The Sun and the solar system are our reference system for abundances of elements and isotopes. Many direct and indirect methods are employed to establish a refined abundance record from the time when the Sun and the Earth were formed. Indications for nucleosynthesis in the local environment when the Sun was formed are derived from meteoritic material and inclusion of radioactive atoms in deep-sea sediments. Spectroscopy at many wavelengths and the neutrino flux from the hydrogen fusion processes in the Sun have established a refined model of how the nuclear energy production shapes stars. Models are required to explore nuclear fusion of heavier elements. These stellar evolution calculations have been confirmed by observations of nucleosynthesis products in the ejecta of stars and supernovae, as captured by stardust grains and by characteristic lines in spectra seen from these objects. One of the successes has been to directly observe gamma rays from radioactive material synthesised in stellar explosions, which fully support the astrophysical models. Another has been the observation of radioactive afterglow and characteristic heavy-element spectrum from a neutron-star merger, confirming the neutron rich environments encountered in such rare explosions. The ejecta material captured by Earth over millions of years in sediments and identified through characteristic radio-isotopes suggests that nearby nucleosynthesis occurred in in recent history, with further indications for sites of specific nucleosynthesis. Together with stardust and diffuse γ rays from radioactive ejecta, these help to piece together how cosmic materials are transported in interstellar space and re-cycled into and between generations of stars. Our description of cosmic compositional evolution needs such observational support, as it rests on several assumptions that appear challenged by recent recognition of violent events being common during evolution of a galaxy. This overview presents the flow of cosmic matter and the various sites of nucleosynthesis, as understood from combining many techniques and observations, towards the current knowledge of how the universe is enriched with elements.
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| 6. |
- Fransson, Claes, et al.
(författare)
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DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A
- 2016
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Ingår i: Astrophysical Journal Letters. - : Institute of Physics Publishing. - 2041-8205 .- 2041-8213. ; 821:1
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Tidskriftsartikel (refereegranskat)abstract
- Both CO and SiO have been observed at early and late phases in SN 1987A. H-2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here, we report the detection of NIR lines from H-2 at 2.12 and 2.40 mu m in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the SN in contrast to Ha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H-2 luminosities, we favor excitation resulting from the Ti-44 decay.
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| 7. |
- Fransson, Claes, et al.
(författare)
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Hubble Space Telescope and Ground-based Observations of SN 1993J and SN 1998S : CNO Processing in the Progenitors
- 2005
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 622, s. 991-1007
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based and Hubble Space Telescope observations are presented for SN 1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar emission lines of N III-V and C III-IV, as well as broad lines from the ejecta. Both the broad ultraviolet and optical lines in SN 1998S indicate an expansion velocity of ~7000 km s-1. The broad emission components of Lyα and Mg II are strongly asymmetrical after day 72 past the explosion and differ in shape from Hα. Different models based on dust extinction from dust in the ejecta or shock region, in combination with Hα from a circumstellar torus, are discussed. It is concluded, however, that the double-peaked line profiles are more likely to arise as a result of optical depth effects in the narrow, cool, dense shell behind the reverse shock than in a torus-like region. The ultraviolet lines of SN 1993J are broad, with a boxlike shape, coming from the ejecta and a cool, dense shell. The shapes of the lines are well fitted by a shell with inner velocity ~7000 km s-1 and outer velocity ~10,000 km s-1. For both SN 1993J and SN 1998S a strong nitrogen enrichment is found, with N/C~12.4 in SN 1993J and N/C~6.0 in SN 1998S. From a compilation of all supernovae with determined CNO ratios, we discuss the implications of these observations for the structure of the progenitors of Type II supernovae. Based in part on observations obtained with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS 5-26555.
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| 8. |
- Fransson, Claes, et al.
(författare)
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Late spectral evolution of the ejecta and reverse shock in SN 1987a
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 768:1, s. 88-
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Tidskriftsartikel (refereegranskat)abstract
- We present observations with the Very Large Telescope and Hubble Space Telescope (HST) of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 February until 2012 January (days 4381-9100 after explosion). We detect broad lines from H alpha, H beta, Mg I], Na I, [O I], [Ca II], and a feature at similar to 9220 angstrom. We identify the latter line with Mg II lambda lambda 9218, 9244, which is most likely pumped by Ly alpha fluorescence. H alpha and H beta both have a centrally peaked component extending to similar to 4500 km s(-1) and a very broad component extending to greater than or similar to 11,000 km s(-1), while the other lines have only the central component. The low-velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar environment, whereas the very broad component comes from faster ejecta passing through the reverse shock, created by the collision with the circumstellar ring. The flux in H alpha from the reverse shock has increased by a factor of four to six from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in the optical lines from the shocked ring. The core component seen in H alpha, [Ca II], and Mg II has experienced a similar increase, which is consistent with that found from HST photometry. The energy deposition of the external X-rays is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. The external X-ray illumination also explains the edge-brightened morphology of the ejecta seen in the HST images. We finally discuss evidence for dust in the ejecta from line asymmetries.
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| 9. |
- Fransson, Claes, et al.
(författare)
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THE DESTRUCTION OF THE CIRCUMSTELLAR RING OF SN 1987A
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 806:1
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Tidskriftsartikel (refereegranskat)abstract
- We present imaging and spectroscopic observations with Hubble Space Telescope and Very Large Telescope of the ring of SN 1987A from 1994 to 2014. After an almost exponential increase of the shocked emission from the hotspots up to day similar to 8000 (similar to 2009), both this and the unshocked emission are now fading. From the radial positions of the hotspots we see an acceleration of these up to 500-1000 km s(-1), consistent with the highest spectroscopic shock velocities from the radiative shocks. In the most recent observations (2013 and 2014), we find several new hotspots outside the inner ring, excited by either X-rays from the shocks or by direct shock interaction. All of these observations indicate that the interaction with the supernova ejecta is now gradually dissolving the hotspots. We predict, based on the observed decay, that the inner ring will be destroyed by similar to 2025.
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| 10. |
- Goobar, Ariel, et al.
(författare)
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Supernova Cosmology : Legacy and Future
- 2011
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Ingår i: Annual Review of Nuclear and Particle Science. - : Annual Reviews. - 0163-8998 .- 1545-4134. ; 61, s. 251-279
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Forskningsöversikt (refereegranskat)abstract
- The discovery of dark energy by the first generation of high-redshift supernova surveys has generated enormous interest beyond cosmology and has dramatic implications for fundamental physics. Distance measurements using supernova explosions are the most direct probes of the expansion history of the universe, making them extremely useful tools with which to study the cosmic fabric and the properties of gravity at the largest scales. The past decade has seen confirmation of the original results. Type Ia supernovae are among the leading techniques to obtain high-precision measurements of the dark energy equation-of-state parameter and, in the near future, its time dependence. The success of these efforts depends on our ability to understand a large number of effects, mostly of an astrophysical nature, that influence the observed flux at Earth. The frontier now lies in understanding whether the observed phenomenon is due to vacuum energy, despite its unnatural density, or some exotic new physics. Future surveys will address the systematic effects with improved calibration procedures and will provide thousands of supernovae for detailed studies.
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| 11. |
- Gröningsson, Per, et al.
(författare)
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High resolution spectroscopy of the inner ring of SN 1987A
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 479:3, s. 761-777
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Tidskriftsartikel (refereegranskat)abstract
- We discuss high resolution VLT/UVES observations (FWHM similar to 6 kms(-1)) from October 2002 (day similar to 5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (similar to 1.5 - 5.0) x 10(3) cm(-3) and temperatures of similar to 6.5 x 10(3) - 2.4 x 104 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [FeXIV]. From a nebular analysis we find that the density in the low ionization region is 4 x 10(6) - 10(7) cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X - XIV], with the latter extending up to similar to- 390 km s(-1) in the blue wing for [Fe XIV], while the low ionization lines extend to typically similar to- 260 km s(-1). For H alpha a faint extension up to similar to- 450 km s(-1) can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are similar to 510 km s(-1). We expect the maximum width of especially the low ionization lines to increase with time.
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| 12. |
- Gröningsson, Per, et al.
(författare)
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High resolution spectroscopy of the line emission from the inner circumstellar ring of SN 1987A and its hot spots
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- We discuss high resolution VLT/UVES observations (FWHM ~ 6 km/s) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (1.5-5.0)E3 cm-3 and temperatures of 6.5E3-2.4E4 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4E6-1E7 cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X-XIV], with the latter extending up to ~ -390 km/s in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~ -260 km/s. For H-alpha a faint extension up to ~ -450 km/s can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool down, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~ 510 km/s. We expect the maximum width of especially the low ionization lines to increase with time.
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| 13. |
- Gröningsson, Per, et al.
(författare)
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Time evolution of the line emission from the inner circumstellar ring of SN 1987A and its hot spots
- 2008
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 492:2, s. 481-491
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Tidskriftsartikel (refereegranskat)abstract
- We present seven epochs between October 1999 and November 2007 of high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A.
The fluxes of most of the narrow lines from the unshocked gas decreased by a factor of 2-3 during this period, consistent with the decay from the initial ionization by the shock break-out. However, [O III] in particular shows an increase up to day ~6800. This agrees with radiative shock models where the pre-shocked gas is heated by the soft X-rays from the shock. The evolution of the [O III] line ratio shows a decreasing temperature of the unshocked ring gas, consistent with a transition from a hot, low density component which was heated by the initial flash ionization to the lower temperature in the pre-ionized gas ahead of the shocks.
The line emission from the shocked gas increases rapidly as the shock sweeps up more gas. We find that the neutral and high ionization lines follow the evolution of the Balmer lines roughly, while the intermediate ionization lines evolve less rapidly. Up to day ~6800, the optical light curves have a similar evolution to that of the soft X-rays. The break between day 6500 and day 7000 for [O III] and [Ne III] is likely due to recombination to lower ionization levels. Nevertheless, the evolution of the [Fe XIV] line, as well as the lines from the lowest ionization stages, continue to follow that of the soft X-rays, as expected.
There is a clear difference in the line profiles between the low and intermediate ionization lines, and those from the coronal lines at the earlier epochs. This shows that these lines arise from regions with different physical conditions, with at least a fraction of the coronal lines coming from adiabatic shocks. At later epochs the line widths of the low ionization lines, however, increase and approach those of the high ionization lines of [ Fe X-XIV] . The H line profile can be traced up to ~500 km s-1 at the latest epoch. This is consistent with the cooling time of shocks propagating into a density of (1-4) 104 cm-3. This means that these shocks are among the highest velocity radiative shocks observed.
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| 14. |
- Johansson, Joel, 1984-
(författare)
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Sources of Dust Extinction in Type Ia Supernovae : Measurements and constraints from X-rays to the Infrared
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The use of Type Ia supernovae (SNe Ia) as distance indicators is essential for studying the expansion history of the Universe and for exploring the nature of dark energy. However, a lack of understanding of the progenitor systems and the empirically derived colour-brightness corrections represent severe limitations for SNe Ia as cosmological probes. In this thesis, we study how dust along the line of sight towards SNe Ia affects the observed light over a wide range of wavelengths; from X-rays to infrared.Unless properly corrected for, the existence of intergalactic dust will introduce a redshift dependent magnitude offset to standard candle sources and bias the cosmological parameter estimates as derived from observations of SNe Ia. We model the optical extinction and X-ray scattering properties of intergalactic dust grains to constrain the intergalactic opacity using a combined analysis of observed quasar colours and measurements of the soft X-ray background. We place upper limits on the extinction AB(z = 1) < 0.10 - 0.25 mag, and the dust density parameter Ωdust < 10−5 − 10−4 (ρgrain/3 g cm−3), for models with RV < 12 − ∞, respectively.Dust in the host galaxies, and dust that may reside in the circumstellar (CS) environment, have important implications for the observed colours of SNe Ia. Using the Hubble Space Telescope and several ground based telescopes, we measure the extinction law, from UV to NIR, for a sample of six nearby SNe Ia. The SNe span a range of E(B − V ) ≈ 0.1 − 1.4 mag and RV ≈ 1.5 − 2.7, showing a diversity of dust extinction parameters. We present mid- and far-infrared (IR) observations for a number of SNe Ia, obtained with the Herschel Space Observatory and Spitzer Space Telescope, addressing CS dust as an explanation for “peculiar” extinction towards some SNe Ia. No excess IR emission is detected, limiting CS dust masses, Mdust < 10−5 solar masses. In particular, the timely appearance of SN 2014J in M82 - the closest SN Ia in several decades - allows for detailed studies, across an unprecedented wavelength range, of its lightcurve and spectral evolution along with the host galaxy and CS environment.
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| 15. |
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| 16. |
- Larsson, Josefin, et al.
(författare)
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The morphology of the ejecta in supernova 1987a : A study over time and wavelength
- 2013
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 768:1, s. 89-
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of the morphology of the ejecta in Supernova 1987A based on images and spectra from the Hubble Space Telescope (HST) as well as integral field spectroscopy from VLT/SINFONI. The HST observations were obtained between 1994 and 2011 and primarily probe the outer H-rich zones of the ejecta. The SINFONI observations were obtained in 2005 and 2011 and instead probe the [Si I]+[Fe II] emission from the inner regions. We find a strong temporal evolution of the morphology in the HST images, from a roughly elliptical shape before similar to 5000 days, to a more irregular, edge-brightened morphology with a "hole" in the middle thereafter. This transition is a natural consequence of the change in the dominant energy source powering the ejecta, from radioactive decay before similar to 5000 days to X-ray input from the circumstellar interaction thereafter. The [Si I]+[Fe II] images display a more uniform morphology, which may be due to a remaining significant contribution from radioactivity in the inner ejecta and the higher abundance of these elements in the core. Both the Ha and the [Si I]+[Fe II] line profiles show that the ejecta are distributed fairly close to the plane of the inner circumstellar ring, which is assumed to define the rotational axis of the progenitor star. The Ha emission extends to higher velocities than [Si I]+[Fe II], as expected from theoretical models. There is no clear symmetry axis for all the emission. Instead, we find that the emission is concentrated to clumps and that the emission is distributed somewhat closer to the ring in the north than in the south. This north-south asymmetry may be partially explained by dust absorption. We compare our results with explosion models and find some qualitative agreement, but note that the observations show a higher degree of large-scale asymmetry.
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| 17. |
- Lundqvist, Peter, et al.
(författare)
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Hydrogen and helium in the spectra of Type Ia supernovae
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 435:1, s. 329-345
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Tidskriftsartikel (refereegranskat)abstract
- We present predictions for hydrogen and helium emission line luminosities from circumstellar matter around Type Ia supernovae (SNe Ia) using time dependent photoionization modelling. Early high-resolution ESO/Very Large Telescope (VLT) optical echelle spectra of the SN Ia 2000cx were taken before and up to similar to 70 d after maximum to probe the existence of such narrow emission lines from the supernova. We detect no such lines, and from our modelling place an upper limit on the mass-loss rate for the putative wind from the progenitor system,. M less than or similar to 1.3 x 10(-5) M-circle dot yr(-1), assuming a speed of 10 km s(-1) and solar abundances for the wind. If the wind would be helium-enriched and/or faster, the upper limit on. M could be significantly higher. In the helium-enriched case, we show that the best line to constrain the mass-loss would be He I.10 830. In addition to confirming the details of interstellar Na I and Ca II absorption towards SN 2000cx as discussed by Patat et al., we also find evidence for 6613.56 angstrom diffuse interstellar band absorption in the Milky Way. We also discuss measurements of the X-ray emission from the interaction between the supernova ejecta and the wind and we re-evaluate observations of SN 1992A obtained similar to 16 d after maximum by Schlegel & Petre. We find an upper limit of. M less than or similar to 1.3 x 10(-5) M-circle dot yr(-1) which is significantly higher than that estimated by Schlegel & Petre. These results, together with the previous observational work on the normal SNe Ia 1994D and 2001el, disfavour a symbiotic star in the upper mass-loss rate regime (so-called Mira-type systems) from being the likely progenitor scenario for these SNe. Our model calculations are general, and can also be used for the subclass of SNe Ia that do show circumstellar interaction, e. g. the recent PTF 11kx. To constrain hydrogen in late-time spectra, we present ESO/VLT and ESO/New Technology Telescope optical and infrared observations of SNe Ia 1998bu and 2000cx in the nebular phase, 251-388 d after maximum. We see no signs of hydrogen line emission in SNe 1998bu and 2000cx at these epochs, and from the absence of Ha with a width of the order of similar to 10(3) km s(-1), we argue from modelling that the mass of such hydrogen-rich gas must be less than or similar to 0.03 M circle dot for both supernovae. Comparing similar upper limits with recent models of Pan et al., it seems that hydrogen-rich donors with a separation of less than or similar to 5 times the radius of the donor may be ruled out for the five SNe Ia 1998bu, 2000cx, 2001el, 2005am and 2005cf. Larger separation, helium-rich donors, or a double-degenerate origin for these supernovae seems more likely. Our models have also been used to put the limit on hydrogen-rich gas in the recent SN 2011fe, and for this supernova, a double-degenerate origin seems likely.
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| 18. |
- Marion, G. H., et al.
(författare)
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TYPE IIb SUPERNOVA SN 2011dh : SPECTRA AND PHOTOMETRY FROM THE ULTRAVIOLET TO THE NEAR-INFRARED
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 781:2, s. 69-
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Tidskriftsartikel (refereegranskat)abstract
- We report spectroscopic and photometric observations of the Type IIb SN 201 ldh obtained between 4 and 34 days after the estimated date of explosion (May 31.5 UT). The data cover a wide wavelength range from 2000 angstrom in the ultraviolet (UV) to 2.4 mu m in the near-infrared (NIR). Optical spectra provide line profiles and velocity measurements of H I, He I, Call, and Fe It that trace the composition and kinematics of the supernova (SN). NIR spectra show that helium is present in the atmosphere as early as 11 days after the explosion. A UV spectrum obtained with the Space Telescope Imaging Spectrograph reveals that the UV flux for SN 2011dh is low compared to other SN IIb. Modeling the spectrum with SYNOW suggests that the UV deficit is due to line blanketing from TinH and Co II. The HI and He I velocities in SN 2011dh are separated by about 4000 km s(-1) at all phases. A velocity gap is consistent with models for a preexplosion structure in which a hydrogen-rich shell surrounds the progenitor. We estimate that the H shell of SN 2011dh is approximate to 8 times less massive than the shell of SN 1993J and approximate to 3 times more massive than the shell of SN 2008ax. Light curves (LCs) for 12 passbands are presented: UVW2, UVM2, UVW1, U, u', B, V, r', i', J, H, and Ks. In the B band, SN 2011dh reached peak brightness of 13.17 mag at 20.0 +/- 0.5 after the explosion. The maximum bolometric luminosity of 1.8 +/- 0.2 x 10(42) erg s(-1) occurred approximate to 22 days after the explosion. NIR emission provides more than 30% of the total bolometric flux at the beginning of our observations, and the NIR contribution increases to nearly 50% of the total by day 34. The UV produces 16% of the total flux on day 4, 5% on day 9, and 1% on day 34. We compare the bolometric LCs of SN 2011dh, SN 2008ax, and SN 1993J. The LC are very different for the first 12 days after the explosions, but all three SN IIb display similar peak luminosities, times of peak, decline rates, and colors after maximum. This suggests that the progenitors of these SN IIb may have had similar compositions and masses, but they exploded inside hydrogen shells that have a wide range of masses. SN 2011dh was well observed, and a likely progenitor star has been identified in preexplosion images. The detailed observations presented here will help evaluate theoretical models for this SN and lead to a better understanding of SN IIb.
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| 19. |
- Nobili, Serena, 1971-
(författare)
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Tests for systematic effects in supernova cosmology
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type~Ia supernovae are used as standard candles to measure the energy density components of the universe. This led to the new paradigm in cosmology: only about 30\% of the universe is made by ordinary pressure-less matter, the rest is associated with an unknown form of energy with a negative equation of state parameter, called dark energy, able to drive the accelaration of the universe. The importance of this discovery requires to fully understand and control the possible systematic effects affecting both current and future measurements, aiming at probing the equation of state parameter, i.e. the nature of dark energy.In this thesis, we tackle systematic effects involved in several aspects of supernova cosmology. Studies of supernova colours are used for investigating the homogeneity of the standard candle and to improve the spectral templates used for $K$-corrections. We have measured the intrinsic colour dispersion and assessed its correlation between different epochs of supernova evolution. We develop a technique for fitting the $I$-band ligthcurve and present studies of correlations of its properties with the SN luminosity. Moreover, we present a pioneer study of restframe $I$-band Hubble diagram extended at redshift $\sim$ 0.5. This is found to be a valuable complementary tool for cosmological studies, and the results found are consistent with the concordance model of the universe, though the uncertainties are large. Presence of grey dust in the intergalactic medium is investigated both using the $I$-band Hubble diagram and supernova colour excess. Although the low statistics of the high redshift sample used do not allow to draw firm conclusions, both methods are tested and shown to be useful for probing the presence of intergalactic dust. The hypothesis of supernova population drift is tested in two different ways, both studying restframe $I$-band lightcurve properties and by comparing spectra of high redshift with those of nearby SNe. One distant supernova SN~2002fd (z=0.279) shows spectral similarities with 1991T/1999aa like objects. No signs of evolution in supernova properties is found in these studies, strengthening our confidence in the measured cosmological parameters.
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| 20. |
- Wang, Xiaofeng, et al.
(författare)
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Evidence for type ia supernova diversity from ultraviolet observations with the hubble space telescope
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 749:2, s. 126-
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Tidskriftsartikel (refereegranskat)abstract
- We present ultraviolet (UV) spectroscopy and photometry of four Type Ia supernovae (SNe 2004dt, 2004ef, 2005M, and 2005cf) obtained with the UV prism of the Advanced Camera for Surveys on the Hubble Space Telescope. This data set provides unique spectral time series down to 2000 angstrom. Significant diversity is seen in the near-maximum-light spectra (similar to 2000-3500 angstrom) for this small sample. The corresponding photometric data, together with archival data from Swift Ultraviolet/Optical Telescope observations, provide further evidence of increased dispersion in the UV emission with respect to the optical. The peak luminositiesmeasured in the uvw1/F250W filter are found to correlate with the B-band light-curve shape parameter Delta m(15)(B), but with much larger scatter relative to the correlation in the broadband B band (e.g., similar to 0.4 mag versus similar to 0.2 mag for those with 0.8 mag < Delta m(15)(B) < 1.7 mag). SN 2004dt is found as an outlier of this correlation (at > 3 sigma), being brighter than normal SNe Ia such as SN 2005cf by similar to 0.9 mag and similar to 2.0 mag in the uvw1/F250W and uvm2/F220W filters, respectively. We show that different progenitor metallicity or line-expansion velocities alone cannot explain such a large discrepancy. Viewing-angle effects, such as due to an asymmetric explosion, may have a significant influence on the flux emitted in the UV region. Detailed modeling is needed to disentangle and quantify the above effects.
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