| 1. |
- Acharyya, A., et al.
(författare)
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Monte Carlo studies for the optimisation of the Cherenkov Telescope Array layout
- 2019
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 111, s. 35-53
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Tidskriftsartikel (refereegranskat)abstract
- The Cherenkov Telescope Array (CTA) is the major next-generation observatory for ground-based veryhigh-energy gamma-ray astronomy. It will improve the sensitivity of current ground-based instruments by a factor of five to twenty, depending on the energy, greatly improving both their angular and energy resolutions over four decades in energy (from 20 GeV to 300 TeV). This achievement will be possible by using tens of imaging Cherenkov telescopes of three successive sizes. They will be arranged into two arrays, one per hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We present here the optimised and final telescope arrays for both CTA sites, as well as their foreseen performance, resulting from the analysis of three different large-scale Monte Carlo productions.
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| 2. |
- Pastorello, A., et al.
(författare)
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A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (a.k.a. ASASSN-18mr). It was discovered about ten days before the maximum light (on MJD = 58 293.4 +/- 5.7 in the V band, with M-V = -18.13 +/- 0.15 mag). The multiband light curves show an immediate post-peak decline with some minor luminosity fluctuations, followed by a flattening starting about 40 days after maximum. The early spectra are relatively blue and show narrow Balmer lines with P Cygni profiles. Additionally, Fe II, O I, He I, and Ca II are detected. The spectra show little evolution with time and with intermediate-width features becoming progressively more prominent, indicating stronger interaction of the SN ejecta with the circumstellar medium. The inspection of archival images from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey has revealed a variable source at the SN position with a brightest detection in December 2015 at M-r = -14.66 +/- 0.17 mag. This was likely an eruptive phase from the massive progenitor star that started from at least mid-2011, and that produced the circumstellar environment within which the star exploded as a Type IIn SN. The overall properties of SN 2018cnf closely resemble those of transients such as SN 2009ip. This similarity favours a massive hypergiant, perhaps a luminous blue variable, as progenitor for SN 2018cnf.
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| 3. |
- Pastorello, A., et al.
(författare)
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Luminous red novae : Stellar mergers or giant eruptions?
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 630
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Tidskriftsartikel (refereegranskat)abstract
- We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490-2011OT1, M 101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H alpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (similar to 6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H alpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.
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| 4. |
- Andrews, Jennifer E., et al.
(författare)
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SN 2017gmr : An Energetic Type II-P Supernova with Asymmetries
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 885:1
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Tidskriftsartikel (refereegranskat)abstract
- We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN;2017gmr from hours after discovery through the first 180 days. SN;2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ?500 R progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130;;0.026 M of Ni-56 are present, if the light curve is solely powered by radioactive decay, although the Ni-56 mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of H? and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.
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| 5. |
- Cai, Y.-Z., et al.
(författare)
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Intermediate-luminosity red transients : Spectrophotometric properties and connection to electron-capture supernova explosions
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 654
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Tidskriftsartikel (refereegranskat)abstract
- We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between −11.5 and −14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5–9.0 × 1040 erg s−1 and their total radiated energies are on the order of (0.3–3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10−4 to 10−3 M⊙. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s−1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.
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| 6. |
- Thilker, David A., et al.
(författare)
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PHANGS–JWST First Results : The Dust Filament Network of NGC 628 and Its Relation to Star Formation Activity
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 944:2
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Tidskriftsartikel (refereegranskat)abstract
- PHANGS–JWST mid-infrared (MIR) imaging of nearby spiral galaxies has revealed ubiquitous filaments of dust emission in intricate detail. We present a pilot study to systematically map the dust filament network (DFN) at multiple scales between 25 and 400 pc in NGC 628. MIRI images at 7.7, 10, 11.3, and 21 μm of NGC 628 are used to generate maps of the filaments in emission, while PHANGS–HST B-band imaging yields maps of dust attenuation features. We quantify the correspondence between filaments traced by MIR thermal continuum/polycyclic aromatic hydrocarbon (PAH) emission and filaments detected via extinction/scattering of visible light; the fraction of MIR flux contained in the DFN; and the fraction of H ii regions, young star clusters, and associations within the DFN. We examine the dependence of these quantities on the physical scale at which the DFN is extracted. With our highest-resolution DFN maps (25 pc filament width), we find that filaments in emission and attenuation are cospatial in 40% of sight lines, often exhibiting detailed morphological agreement; that ∼30% of the MIR flux is associated with the DFN; and that 75%–80% of the star formation in H ii regions and 60% of the mass in star clusters younger than 5 Myr are contained within the DFN. However, the DFN at this scale is anticorrelated with looser associations of stars younger than 5 Myr identified using PHANGS–HST near-UV imaging. We discuss the impact of these findings on studies of star formation and the interstellar medium, and the broad range of new investigations enabled by multiscale maps of the DFN.
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