| 1. |
- Adams, S. M., et al.
(författare)
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iPTF Survey for Cool Transients
- 2018
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 130:985
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Tidskriftsartikel (refereegranskat)abstract
- We performed a wide-area (2000 deg2) g and I band experiment as part of a two month extension to the Intermediate Palomar Transient Factory. We discovered 36 extragalactic transients including iPTF17lf, a highly reddened local SN Ia, iPTF17bkj, a new member of the rare class of transitional Ibn/IIn supernovae, and iPTF17be, a candidate luminous blue variable outburst. We do not detect any luminous red novae and place an upper limit on their rate. We show that adding a slow-cadence I band component to upcoming surveys such as the Zwicky Transient Facility will improve the photometric selection of cool and dusty transients.
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| 2. |
- Ahrens, Maryon, et al.
(författare)
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Multi-messenger Observations of a Binary Neutron Star Merger
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 848:2
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Tidskriftsartikel (refereegranskat)abstract
- On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.
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| 3. |
- Amanullah, Rahman, et al.
(författare)
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Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 μm
- 2015
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 453:3, s. 3300-3328
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Tidskriftsartikel (refereegranskat)abstract
- We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2-2 mu m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction R-V. In particular, we note that for the two SNe with E(B - V) greater than or similar to 1 mag, for which the colour excess is dominated by dust extinction, we find R-V = 1.4 +/- 0.1 and R-V = 2.8 +/- 0.1. Adding UV photometry reduces the uncertainty of fitted R-V by similar to 50 per cent allowing us to also measure R-V of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.
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| 4. |
- Andreoni, I., et al.
(författare)
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Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes
- 2017
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Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 34
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Forskningsöversikt (refereegranskat)abstract
- The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (similar to 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
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| 5. |
- Barack, Leor, et al.
(författare)
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Black holes, gravitational waves and fundamental physics : a roadmap
- 2019
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Ingår i: Classical and quantum gravity. - : IOP Publishing. - 0264-9381 .- 1361-6382. ; 36:14
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Forskningsöversikt (refereegranskat)abstract
- The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.
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| 6. |
- Bellm, Eric C., et al.
(författare)
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The Zwicky Transient Facility : Surveys and Scheduler
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:1000
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel algorithm for scheduling the observations of time-domain imaging surveys. Our integer linear programming approach optimizes an observing plan for an entire night by assigning targets to temporal blocks, enabling strict control of the number of exposures obtained per field and minimizing filter changes. A subsequent optimization step minimizes slew times between each observation. Our optimization metric self-consistently weights contributions from time-varying airmass, seeing, and sky brightness to maximize the transient discovery rate. We describe the implementation of this algorithm on the surveys of the Zwicky Transient Facility and present its on-sky performance.
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| 7. |
- Bellm, Eric C., et al.
(författare)
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The Zwicky Transient Facility : System Overview, Performance, and First Results
- 2019
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 131:995
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Tidskriftsartikel (refereegranskat)abstract
- The Zwicky Transient Facility (ZTF) is a new optical time-domain survey that uses the Palomar 48 inch Schmidt telescope. A custom-built wide-field camera provides a 47 deg(2) field of view and 8 s readout time, yielding more than an order of magnitude improvement in survey speed relative to its predecessor survey, the Palomar Transient Factory. We describe the design and implementation of the camera and observing system. The ZTF data system at the Infrared Processing and Analysis Center provides near-real-time reduction to identify moving and varying objects. We outline the analysis pipelines, data products, and associated archive. Finally, we present on-sky performance analysis and first scientific results from commissioning and the early survey. ZTF's public alert stream will serve as a useful precursor for that of the Large Synoptic Survey Telescope.
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| 8. |
- Bulla, Mattia, et al.
(författare)
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Estimating dust distances to Type Ia supernovae from colour excess time evolution
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 473:2, s. 1918-1929
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Tidskriftsartikel (refereegranskat)abstract
- We present a new technique to infer dust locations towards reddened Type Ia supernovae and to help discriminate between an interstellar and a circumstellar origin for the observed extinction. Using Monte Carlo simulations, we show that the time evolution of the light-curve shape and especially of the colour excess E(B - V) places strong constraints on the distance between dust and the supernova. We apply our approach to two highly reddened Type Ia supernovae for which dust distance estimates are available in the literature: SN 2006X and SN 2014J. For the former, we obtain a time-variable E(B - V) and from this derive a distance of 27.5(-4.9)(+ 9.0) or 22.1(-3.8)(+ 6.0) pc depending on whether dust properties typical of the Large Magellanic Cloud (LMC) or the Milky Way (MW) are used. For the latter, instead, we obtain a constant E(B - V) consistent with dust at distances larger than similar to 50 and 38 pc for LMC-and MW-type dust, respectively. Values thus extracted are in excellent agreement with previous estimates for the two supernovae. Our findings suggest that dust responsible for the extinction towards these supernovae is likely to be located within interstellar clouds. We also discuss how other properties of reddened Type Ia supernovae - such as their peculiar extinction and polarization behaviour and the detection of variable, blue-shifted sodium features in some of these events - might be compatible with dust and gas at interstellar-scale distances.
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| 9. |
- Bulla, Mattia, et al.
(författare)
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Shedding light on the Type Ia supernova extinction puzzle : dust location found
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 479:3, s. 3663-3674
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Tidskriftsartikel (refereegranskat)abstract
- The colour evolution of reddened Type Ia supernovae can place strong constraints on the location of dust and help address the question of whether the observed extinction stems from the interstellar medium or from circumstellar material surrounding the progenitor. Here, we analyse BV photometry of 48 reddened Type Ia supernovae from the literature and estimate the dust location from their B - V colour evolution. We find a time-variable colour excess E(B - V) for 15 supernovae in our sample and constrain dust to distances between 0.013 and 45 pc (4 x 10(16)-10(20) cm). For the remaining supernovae, we obtain a constant E(B - V) evolution and place lower limits on the dust distance from the explosion. In all the 48 supernovae, the inferred dust location is compatible with an interstellar origin for the extinction. This is corroborated by the observation that supernovae with relatively nearby dust (less than or similar to 1 pc) are located close to the centre of their host galaxy in high-density dusty regions, where interactions between the supernova radiation and interstellar clouds close by are likely to occur. For supernovae showing time-variable E(B - V), we identify a potential preference for low-R-V values, unusually strong sodium absorption, and blue-shifted and time-variable absorption features. Within the interstellar framework, this brings evidence to a proposed scenario, where cloud-cloud collisions induced by the supernova radiation pressure can shift the grain size distribution to smaller values and enhance the abundance of sodium in the gaseous phase.
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| 10. |
- Cao, Yi, et al.
(författare)
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A strong ultraviolet pulse from a newborn type Ia supernova
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 521:7552, s. 328-
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Tidskriftsartikel (refereegranskat)abstract
- Type Ia supernovae(1) are destructive explosions of carbon-oxygen white dwarfs(2,3). Although they are used empirically to measure cosmological distances(4-6), the nature of their progenitors remains mysterious(3). One of the leading progenitor models, called the single degenerate channel, hypothesizes that a white dwarf accretes matter from a companion star and the resulting increase in its central pressure and temperature ignites thermonuclear explosion(3,7,8). Here we report observations with the Swift Space Telescope of strong but declining ultraviolet emission from a type Ia supernova within four days of its explosion. This emission is consistent with theoretical expectations of collision between material ejected by the supernova and a companion star(9), and therefore provides evidence that some type Ia supernovae arise from the single degenerate channel.
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| 11. |
- Cao, Yi, et al.
(författare)
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ABSENCE OF FAST-MOVING IRON IN AN INTERMEDIATE TYPE Ia SUPERNOVA BETWEEN NORMAL AND SUPER-CHANDRASEKHAR
- 2016
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 823:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report observations of a peculiar SN Ia iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show an absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv's light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band Delta m(15)=1.03 +/- 0.01) and overall spectral features resemble those of normal SNe Ia. On the other hand, its large peak optical and UV luminosity (M-B = -19.84 mag, M-uvm2 = -15.5 mag) and its low but almost constant Si II velocities of about 10,000 km s (1) are similar to those in super-Chandrasekhar events, and its persistent carbon signatures in the spectra are weaker than those seen commonly in super-Chandrasekhar events. We estimate a Ni-56 mass of 0.81(-0.18)(+0.10) M-circle dot and a total ejecta mass of 1.59(-0.12)(+0.45) M-circle dot. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.
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| 12. |
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| 13. |
- Coughlin, Michael W., et al.
(författare)
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GROWTH on S190425z : Searching Thousands of Square Degrees to Identify an Optical or Infrared Counterpart to a Binary Neutron Star Merger with the Zwicky Transient Facility and Palomar Gattini-IR
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 885:1
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Tidskriftsartikel (refereegranskat)abstract
- The third observing run by LVC has brought the discovery of many compact binary coalescences. Following the detection of the first binary neutron star merger in this run (LIGO/Virgo S190425z), we performed a dedicated follow-up campaign with the Zwicky Transient Facility (ZTF) and Palomar Gattini-IR telescopes. The initial skymap of this single-detector gravitational wave (GW) trigger spanned most of the sky observable from Palomar Observatory. Covering 8000 deg(2) of the initial skymap over the next two nights, corresponding to 46% integrated probability, ZTF system achieved a depth of 21 m(AB) in g- and r-bands. Palomar Gattini-IR covered 2200 square degrees in J-band to a depth of 15.5 mag, including 32% integrated probability based on the initial skymap. The revised skymap issued the following day reduced these numbers to 21% for the ZTF and 19% for Palomar Gattini-IR. We narrowed 338,646 ZTF transient ?alerts? over the first two nights of observations to 15 candidate counterparts. Two candidates, ZTF19aarykkb and ZTF19aarzaod, were particularly compelling given that their location, distance, and age were consistent with the GW event, and their early optical light curves were photometrically consistent with that of kilonovae. These two candidates were spectroscopically classified as young core-collapse supernovae. The remaining candidates were ruled out as supernovae. Palomar Gattini-IR did not identify any viable candidates with multiple detections only after merger time. We demonstrate that even with single-detector GW events localized to thousands of square degrees, systematic kilonova discovery is feasible.
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| 14. |
- Dhawan, Suhail, et al.
(författare)
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iPTF16abc and the population of Type Ia supernovae : comparing the photospheric, transitional, and nebular phases
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 480:2, s. 1445-1456
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Tidskriftsartikel (refereegranskat)abstract
- Key information about the progenitor system and the explosion mechanism of Type Ia supernovae (SNe Ia) can be obtained from early observations, within a few days from explosion. iPTF16abc was discovered as a young SN Ia with excellent early time data. Here, we present photometry and spectroscopy of the SN in the nebular phase. A comparison of the early time data with a sample of SNe Ia shows distinct features, differing from normal SNe Ia at early phases but similar to normal SNe Ia at a few weeks after maximum light (i.e. the transitional phase) and well into the nebular phase. The transparency time-scales (t0) for this sample of SNe Ia range between ∼25 and 41 d indicating a diversity in the ejecta masses. t0 also weakly correlates with the peak bolometric luminosity, consistent with the interpretation that SNe with higher ejecta masses would produce more 56Ni" role="presentation">56Ni . Comparing the t0 and the maximum luminosity, Lmax distribution of a sample of SNe Ia to predictions from a wide range of explosion models we find an indication that the sub-Chandrasekhar mass models span the range of observed values. However, the bright end of the distribution can be better explained by Chandrasekhar mass delayed detonation models, hinting at multiple progenitor channels to explain the observed bolometric properties of SNe Ia. iPTF16abc appears to be consistent with the predictions from the Mch models.
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| 15. |
- Dhawan, Suhail, et al.
(författare)
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Narrowing down the possible explanations of cosmic acceleration with geometric probes
- 2017
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- Recent re-calibration of the Type Ia supernova (SNe Ia) magnitude-redshift relation combined with cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data have provided excellent constraints on the standard cosmological model. Here, we examine particular classes of alternative cosmologies, motivated by various physical mechanisms, e.g. scalar fields, modified gravity and phase transitions to test their consistency with observations of SNe Ia and the ratio of the angular diameter distances from the CMB and BAO. Using a model selection criterion for a relative comparison of the models (the Bayes Factor), we find moderate to strong evidence that the data prefer flat Lambda CDM over models invoking a thawing behaviour of the quintessence scalar field. However, some exotic models like the growing neutrino mass cosmology and vacuum metamorphosis still present acceptable evidence values. The bimetric gravity model with only the linear interaction term as well as a simplified Galileon model can be ruled out by the combination of SNe Ia and CMB/BAO datasets whereas the model with linear and quadratic interaction terms has a comparable evidence value to standard Lambda CDM. Thawing models are found to have significantly poorer evidence compared to flat Lambda CDM cosmology under the assumption that the CMB compressed likelihood provides an adequate description for these non-standard cosmologies. We also present estimates for constraints from future data and find that geometric probes from oncoming surveys can put severe limits on non-standard cosmological models.
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| 16. |
- Dhawan, Suhail, et al.
(författare)
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The effect of inhomogeneities on dark energy constraints
- 2018
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :7
-
Tidskriftsartikel (refereegranskat)abstract
- Constraints on models of the late time acceleration of the universe assume the cosmological principle of homogeneity and isotropy on large scales. However, small scale inhomogeneities can alter observational and dynamical relations, affecting the inferred cosmological parameters. For precision constraints on the properties of dark energy, it is important to assess the potential systematic effects arising from these inhomogeneities. In this study, we use the Type Ia supernova magnitude-redshift relation to constrain the inhomogeneities as described by the Dyer-Roeder distance relation and the effect they have on the dark energy equation of state (w), together with priors derived from the most recent results of the measurements of the power spectrum of the Cosmic Microwave Background and Baryon Acoustic Oscillations. We find that the parameter describing the inhomogeneities (eta) is weakly correlated with w. The best fit values w = -0.933 +/- 0.065 and eta = 0.61 +/- 0.37 are consistent with homogeneity at < 2 sigma level. Assuming homogeneity (eta = 1), we find w = -0.961 +/- 0.055, indicating only a small change in w. For a time-dependent dark energy equation of state, w(0) = -0.951 +/- 0.112 and w(a) = 0.059 +/- 0.418, to be compared with w(0) = -0.983 +/- 0.127 and w(a) = 0.07 +/- 0.432 in the homogeneous case, which is also a very small change. We do not obtain constraints on the fraction of dark matter in compact objects, f(p), at the 95% C.L. with conservative corrections to the distance formalism. Future supernova surveys will improve the constraints on eta, and hence, f(p), by a factor of similar to 10.
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| 17. |
- Feindt, Ulrich, et al.
(författare)
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simsurvey : estimating transient discovery rates for the Zwicky transient facility
- 2019
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- When planning a survey for astronomical transients, many factors such as cadence, filter choice, sky coverage, and depth of observations need to be balanced in order to optimize the scientific gain of the survey. Here we present a software package called simsurvey for simulating the supernova lightcurves that are expected based on a survey strategy, which can then be used to determine the potential for discoveries of each strategy in question. The code is set up in a modular fashion that allows easy modification of small details of the survey and enables the user to adapt it to any survey design and transient template that they wish to use in planning their survey. As an example of its utility, we use simsurvey to simulate the lightcurve of several types of supernovae that the recently started Zwicky Transient Facility (ZTF) is expected to find and compare the results to the discoveries made during its early operations. We conclude that ZTF will find thousands of bright supernovae per year, of which about 10 could potentially be found with two days of explosion. Over the course of three years the survey will obtain lightcurves of about 1800 type Ia supernovae with z < 0.1 that can be used as distance indicators in cosmology if they are spectroscopically classified using additional telescopes. In a comparison to detections from the ZTF public survey, we found good agreement with the numbers of detections expected from the simulations.
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| 18. |
- Ferretti, Raphael, et al.
(författare)
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No Evidence of Circumstellar Gas Surrounding Type Ia Supernova SN 2017cbv
- 2017
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 851:2
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Tidskriftsartikel (refereegranskat)abstract
- Nearby type Ia supernovae (SNe Ia), such as SN 2017cbv, are useful events to address the question of what the elusive progenitor systems of the explosions are. Hosseinzadeh et al. suggested that the early blue excess of the light curve of SN 2017cbv could be due to the supernova ejecta interacting with a non-degenerate companion star. Some SN Ia progenitor models suggest the existence of circumstellar (CS) environments in which strong outflows create low-density cavities of different radii. Matter deposited at the edges of the cavities should be at distances at which photoionization due to early ultraviolet (UV) radiation of SNe. Ia causes detectable changes to the observable Na I D and Ca II H&K absorption lines. To study possible narrow absorption lines from such material, we obtained a time series of high-resolution spectra of SN 2017cbv at phases between -14.8 and +83 days with respect to B-band maximum, covering the time at which photoionization is predicted to occur. Both narrow Na I D and Ca II H&K are detected in all spectra, with no measurable changes between the epochs. We use photoionization models to rule out the presence of Na I and Ca II gas clouds along the line of sight of SN 2017cbv between similar to 8 x 10(16)-2 x 10(19) cm and similar to 10(15)-10(17) cm, respectively. Assuming typical abundances, the mass of a homogeneous spherical CS gas shell with radius R must be limited to M-HI(CSM) < 3 x 10(-4) x (R/10(17)[cm(2)]) M-circle dot. The bounds point to progenitor models that deposit little gas in their CS environment.
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| 19. |
- Ferretti, Raphael, et al.
(författare)
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Probing gas and dust in the tidal tail of NGC 5221 with the type Ia supernova iPTF16abc
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 606
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Tidskriftsartikel (refereegranskat)abstract
- Context. Type Ia supernovae (SNe Ia) can be used to address numerous questions in astrophysics and cosmology. Due to their wellknown spectral and photometric properties, SNe Ia are well suited to study gas and dust along the lines-of-sight to the explosions. For example, narrow Na I D and Ca II H&K absorption lines can be studied easily, because of the well-defined spectral continuum of SNe Ia around these features.Aims. We aim to study the gas and dust along the line-of-sight to iPTF16abc, which occurred in an unusual location, in a tidal arm, 80 kpc from centre of the galaxy NGC 5221.Methods. Using a time-series of high-resolution spectra, we have examined narrow Na I D and Ca II H&K absorption features for variations in time, which would be indicative for circumstellar (CS) matter. Furthermore, we have taken advantage of the well known photometric properties of SNe Ia to determine reddening due to dust along the line-of-sight.Results. From the lack of variations in Na I D and Ca II H&K, we determine that none of the detected absorption features originate from the CS medium of iPTF16abc. While the Na I D and Ca II H&K absorption is found to be optically thick, a negligible amount of reddening points to a small column of interstellar dust.Conclusions. We find that the gas along the line-of-sight to iPTF16abc is typical of what might be found in the interstellar medium (ISM) within a galaxy. It suggests that we are observing gas that has been tidally stripped during an interaction of NGC 5221 with one of its neighbouring galaxies in the past ~109 years. In the future, the gas clouds could become the locations of star formation. On a longer time scale, the clouds might diuse, enriching the circum-galactic medium (CGM) with metals. The gas profile along the line-of-sight should be useful for future studies of the dynamics of the galaxy group containing NGC 5221.
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| 20. |
- Ferretti, Raphael, 1989-
(författare)
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The Circumstellar Environment of Type Ia Supernovae
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Type Ia supernovae (SNe Ia) have proven to be extremely useful for measuring cosmological distances and were used for the discovery of the accelerated expansion of the universe. Although thousands of SNe Ia have been observed to date, many questions surrounding the physics of the explosions and the nature of their progenitor systems remain unanswered. An notable property of many SNe Ia is the relation between extinction due to dust and their colour. For example SN 2014J, the nearest SN Ia in recent years, has an extinction relation which would be very unusual to observe in the Milky Way. One possible explanation to the peculiar extinction could be the presence of circumstellar (CS) dust surrounding the explosions. Incidentally, some proposed progenitor models of SNe Ia suggest that the explosions are surrounded by shells of matter, which could account for the unusual extinction.CS gas would be ionised, if it is exposed to the intense ultraviolet (UV) radiation of a SN Ia. The research presented in this thesis focuses on the search for CS gas by observing the effects of photoionisation on absorption lines commonly detected in optical spectra. Simple models suggest that the frequently studied sodium doublet (Na I D) should significantly decrease or even disappear if the gas is in the CS environment. Conversely, the absence of variations implies that the absorbing gas clouds must be far from the explosion, in the interstellar medium (ISM). To date, few SNe Ia have been shown to have variable absorption lines, to which we have added another case with SN 2013gh. Yet, we have also shown that most observations searching for variable absorption lines have been taken at too late phases, when most CS gas will have already been ionised. Setting out to obtain the earliest possible coverage of a SN Ia with high-resolution spectra, we have been able to set strong limits on the presence of CS gas surrounding SN 2017cbv.Along with evidence from other observational methods, these results have shown that there is little matter in the CS environments of SNe Ia, suggesting that the peculiar extinction likely results from the dust properties of their host galaxy ISM. Although the progenitor question cannot be resolved by these observations, nondetections of CS gas point to models which do not deposit large amounts of matter in their surroundings.
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| 21. |
- Ferretti, Raphael, et al.
(författare)
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Time-varying sodium absorption in the Type Ia supernova 2013gh
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Context. Temporal variability of narrow absorption lines in high-resolution spectra of Type Ia supernovae (SNe Ia) is studied to search for circumstellar matter. Time series which resolve the profiles of absorption lines such as Na I D or Ca II H&K are expected to reveal variations due to photoionisation and subsequent recombination of the gases. The presence, composition, and geometry of circumstellar matter may hint at the elusive progenitor system of SNe Ia and could also affect the observed reddening law. Aims. To date, there are few known cases of time-varying Na I D absorption in SNe Ia, all of which occurred during relatively late phases of the supernova (SN) evolution. Photoionisation, however, is predicted to occur during the early phases of SNe Ia, when the supernovae peak in the ultraviolet. We attempt, therefore, to observe early-time absorption-line variations by obtaining high-resolution spectra of SNe before maximum light. Methods. We have obtained photometry and high-resolution spectroscopy of SNe Ia 2013gh and iPTF 13dge, to search for absorption-line variations. Furthermore, we study interstellar absorption features in relation to the observed photometric colours of the SNe. Results. Both SNe display deep Na I D and Ca II H&K absorption features. Furthermore, small but significant variations are detected in a feature of the Na I D profile of SN 2013gh. The variations are consistent with either geometric effects of rapidly moving or patchy gas clouds or photoionisation of Na I gas at R approximate to 10(19) cm from the explosion. Conclusions. Our analysis indicates that it is necessary to focus on early phases to detect photoionisation effects of gases in the circumstellar medium of SNe Ia. Different absorbers such as Na I and Ca II can be used to probe for matter at different distances from the SNe. The nondetection of variations during early phases makes it possible to put limits on the abundance of the species at those distances.
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| 22. |
- Goldstein, Daniel A., et al.
(författare)
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Rates and Properties of Supernovae Strongly Gravitationally Lensed by Elliptical Galaxies in Time-domain Imaging Surveys
- 2019
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 243:1
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Tidskriftsartikel (refereegranskat)abstract
- Supernovae that are strongly gravitationally lensed (gLSNe) by elliptical galaxies are powerful probes of astrophysics and cosmology that will be discovered systematically by wide-field, high-cadence imaging surveys such as the Zwicky Transient Facility (ZTF) and the Large Synoptic Survey Telescope (LSST). Here we use pixel-level simulations that include observing strategy, target selection, supernova properties, and dust to forecast the rates and properties of gLSNe that ZTF and LSST will find. Applying the resolution-insensitive discovery strategy of Goldstein et al., we forecast that ZTF (LSST) can discover 0.02 (0.79) 91bg-like, 0.17 (5.92) 91T-like, 1.22 (47.84) Type Ia, 2.76 (88.51) Type IIP, 0.31 (12.78) Type IIL, and 0.36 (15.43) Type Ib/c gLSNe per year, with uncertainties dominated by uncertainties in the supernova rate. We also forecast that the surveys can discover at least 3.75 (209.32) Type IIn gLSNe per year, for a total of at least 8.60 (380.60) gLSNe per year under fiducial observing strategies. ZTF gLSNe have a median z(s) = 0.9, z(l) = 0.35, vertical bar mu(tot)vertical bar = 30, Delta t(max) = 10 days, min (theta) = 0 ''.25, and N-img = 4. LSST gLSNe are less compact and less magnified, with a median z(s) = 1.0, z(l) = 0.4, vertical bar mu(tot)vertical bar = 6, Delta t(max) = 25 days, min(theta) = 0 ''.6, and N-img = 2. We develop a model of the supernova-host galaxy connection and find that the vast majority of gLSN host galaxies will be multiply imaged, enabling detailed constraints on lens models with sufficiently deep high-resolution imaging taken after the supernova has faded. We release the results of our simulations as catalogs at http://portal.nersc.gov/project/astro250/glsne/.
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| 23. |
- Goobar, Ariel, et al.
(författare)
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CONSTRAINTS ON THE ORIGIN OF THE FIRST LIGHT FROM SN 2014J
- 2015
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 799:1, s. 106-
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Tidskriftsartikel (refereegranskat)abstract
- We study the very early light curve of supernova 2014J (SN 2014J) using the high-cadence broad-band imaging data obtained by the Kilodegree Extremely Little Telescope, which fortuitously observed M 82 around the time of the explosion, starting more than 2 months prior to detection, with up to 20 observations per night. These observations are complemented by observations in two narrow-band filters used in an Ha survey of nearby galaxies by the intermediate Palomar Transient Factory that also captured the first days of the brightening of the supernova. The evolution of the light curves is consistent with the expected signal from the cooling of shock heated material of large scale dimensions, greater than or similar to 1R(circle dot). This could be due to heated material of the progenitor, a companion star or pre-existing circumstellar environment, e.g., in the form of an accretion disk. Structure seen in the light curves during the first days after explosion could also originate from radioactive material in the outer parts of an exploding white dwarf, as suggested from the early detection of gamma-rays. The model degeneracy translates into a systematic uncertainty of +/- 0.3 days on the estimate of the first light from SN 2014J.
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| 24. |
- Goobar, Ariel, et al.
(författare)
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iPTF16geu : A multiply imaged, gravitationally lensed type Ia supernova
- 2017
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 356:6335, s. 291-295
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because the light from the stellar explosion was magnified more than 50 times by the curvature of space around matter in an intervening galaxy. We used high-spatial-resolution observations to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec, smaller than is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration imply close alignment between the lines of sight to the supernova and to the lens. The relative magnifications of the four images provide evidence for substructures in the lensing galaxy.
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| 25. |
- Goobar, Ariel, et al.
(författare)
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The cosmic transparency measured with Type Ia supernovae : implications for intergalactic dust
- 2018
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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. ; 477:1, s. l75-L79
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Tidskriftsartikel (refereegranskat)abstract
- Observations of high-redshift Type Ia supernovae (SNe Ia) are used to study the cosmic transparency at optical wavelengths. Assuming a flat Lambda cold dark matter (Lambda CDM) cosmological model based on baryon acoustic oscillations and cosmic microwave background measurements, redshift dependent deviations of SN Ia distances are used to constrain mechanisms that would dim light. The analysis is based on the most recent Pantheon SN compilation, for which there is a 0.03 +/- 0.01 (stat) mag discrepancy in the distant supernova distance moduli relative to the Lambda CDM model anchored by supernovae at z < 0.05. While there are known systematic uncertainties that combined could explain the observed offset, here we entertain the possibility that the discrepancy may instead be explained by scattering of supernova light in the intergalactic medium (IGM). We focus on two effects: Compton scattering by free electrons and extinction by dust in the IGM. We find that if the discrepancy is entirely due to dimming by dust, the measurements can be modelled with a cosmic dust density Omega(dust)(IGM) = 8 x 10(-5)(1 + z)(-1), corresponding to an average attenuation of 2 x 10(-5) mag Mpc(-1) in V band. Forthcoming SN Ia studies may provide a definitive measurement of the IGM dust properties, while still providing an unbiased estimate of cosmological parameters by introducing additional parameters in the global fits to the observations.
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