| 1. |
- Abramowicz, Marek A, 1945, et al.
(författare)
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Introduction
- 2008
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1387-6473. ; 51
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Abramowicz, Marek A, 1945
(författare)
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Spacetime is not just space and time
- 2008
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1387-6473. ; 51
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Forskningsöversikt (refereegranskat)
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| 3. |
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| 4. |
- Davies, Melvyn B, et al.
(författare)
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Compact binaries, hypernovae, and GRBs
- 2010
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1872-9630 .- 1387-6473. ; 54:3-6, s. 181-182
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Tidskriftsartikel (refereegranskat)abstract
- The collapse of a massive stellar core may lead to the production of a black hole surrounded by a torus of material. Such a system is a potential source for the so-called long gamma-ray bursts (GRBs). A torus will form around the black hole if the infalling material contains sufficient angular momentum. This however requires that the core of the massive star rotates extremely rapidly prior to collapse. Here we explore whether tidal locking within binaries can spin stars up sufficiently. We show that the binaries are required to have separations <= 3-4 R-circle dot, hence the massive star would have lost its outer envelope (for example in a common envelope phase). In addition, the companions to the massive stars must themselves be compact. Comparison with observed tight binaries, which contain either two neutron stars or a neutron star and a white dwarf, shows that angular momentum is likely to have played an important role during the core collapse of the secondary in about half the systems, including the recently-discovered neutron star binary J0737-3039. Even if these systems failed to produce a GRB, as they do not contain a black hole, they are relevant to the problem of GRB production as a very similar evolutionary pathway (but with a slightly more massive helium star core) may well produce a GRB. (C) 2010 Elsevier B.V. All rights reserved.
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| 5. |
- Dravins, Dainis, et al.
(författare)
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Stellar intensity interferometry: Prospects for sub-milliarcsecond optical imaging
- 2012
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1872-9630 .- 1387-6473. ; 56:5, s. 143-167
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Tidskriftsartikel (refereegranskat)abstract
- Using kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the spatial resolution achieved in optical astronomy by an order of magnitude, enabling images of rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial pulsations across stellar surfaces. Intensity interferometry (once pioneered by Hanbury Brown and Twiss) connects telescopes only electronically, and is practically insensitive to atmospheric turbulence and optical imperfections, permitting observations over long baselines and through large air-masses, also at short optical wavelengths. The required large telescopes (similar to 10 m) with very fast detectors (similar to ns) are becoming available as the arrays primarily erected to measure Cherenkov light emitted in air by particle cascades initiated by energetic gamma rays. Planned facilities (e.g., CTA, Cherenkov Telescope Array) envision many tens of telescopes distributed over a few square km. Digital signal handling enables very many baselines (from tens of meters to over a kilometer) to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, in effect synthesizing an optical interferometer in software. Simulated observations indicate limiting magnitudes around m(v) = 8, reaching angular resolutions similar to 30 mu arcsec in the violet. The signal-to-noise ratio favors high-temperature sources and emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral continuum. Intensity interferometry directly provides the modulus (but not phase) of any spatial frequency component of the source image; for this reason a full image reconstruction requires phase retrieval techniques. This is feasible if sufficient coverage of the interferometric (u, v)-plane is available, as was verified through numerical simulations. Laboratory and field experiments are in progress; test telescopes have been erected, intensity interferometry has been achieved in the laboratory, and first full-scale tests of connecting large Cherenkov telescopes have been carried out. This paper reviews this interferometric method in view of the new possibilities offered by arrays of air Cherenkov telescopes, and outlines observational programs that should become realistic already in the rather near future. (C) 2012 Elsevier B.V. All rights reserved.
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| 6. |
- Feltzing, Sofia, et al.
(författare)
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Elemental abundances in the Milky Way stellar disk(s), bulge, and halo
- 2013
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1872-9630 .- 1387-6473. ; 57:3-4, s. 80-99
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Tidskriftsartikel (refereegranskat)abstract
- We present a review of elemental abundances in the Milky Way stellar disk, bulge, and halo with a focus on data derived from high-resolution stellar spectra. These data are fundamental in disentangling the formation history and subsequent evolution of the Milky Way. Information from such data is still limited and confined to narrowly defined stellar samples. The astrometric Gala satellite will soon be launched by the European Space Agency. Its final data set will revolutionize information on the motions of a billion stars in the Milky Way. This will be complemented by several ground-based observational campaigns, in particular spectroscopic follow-up to study elemental abundances in the stars in detail. Our review shows the very rich and intriguing picture built from rather small and local samples. The Gaia data deserve to be complemented by data of the same high quality that have been collected for the solar neighborhood. (C) 2013 Elsevier B.V. All rights reserved.
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| 7. |
- Iliev, Ilian T., et al.
(författare)
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kSZ from patchy reionization: The view from the simulations
- 2006
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1387-6473. ; 50:11-12, s. 909-917
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Tidskriftsartikel (refereegranskat)abstract
- We present the first calculation of the kinetic Sunyaev Zel’dovich (kSZ) effect due to the inhomogeneus reionization of the universe based on detailed large-scale radiative transfer simulations of reionization. The resulting sky power spectra peak at ℓ = 2000 8000 with maximum values of [ℓ(ℓ + 1)Cℓ/(2π)]max ˜ 4 7 × 10^‑13. The scale roughly corresponds to the typical ionized bubble sizes observed in our simulations, of ˜5 20 Mpc. The kSZ anisotropy signal from reionization dominates the primary CMB signal above ℓ = 3000. At large-scales the patchy kSZ signal depends only on the source efficiencies. It is higher when sources are more efficient at producing ionizing photons, since such sources produce larger ionized regions, on average, than less efficient sources. The introduction of sub-grid gas clumping in the radiative transfer simulations produce significantly more power at small-scales, but has little effect at large-scales. The patchy reionization kSZ signal is dominated by the post-reionization signal from fully-ionized gas, but the two contributions are of similar order at scales ℓ ˜ 3000 ‑ 10^4, indicating that the kSZ anisotropies from reionization are an important component of the total kSZ signal at these scales.
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| 8. |
- Johansson, Sveneric, et al.
(författare)
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Astrophysical lasers and nonlinear optical effects in space
- 2007
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Ingår i: New Astronomy Reviews. - : Elsevier BV. - 1872-9630 .- 1387-6473. ; 51:5-6, s. 443-523
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Forskningsöversikt (refereegranskat)abstract
- The present state of the art concerning astrophysical lasers (APL) and nonlinear optical effects under astrophysical conditions is reviewed. The operational conditions of an APL (amplification under non-LTE conditions) and astrophysical predecessors of the laboratory lasers are considered in the introduction of the review. The rareness of observed APL action in the visible range in comparison with astrophysical masers (APM) in the microwave range is explained. Early proposals of APLs with collisional and optical pumping are discussed. APL/M in the mid-IR and submillimeter ranges linking APL and APM are also discussed. APLs in the Weigelt blobs of Eta Carinae operating in Fell and 01 with a Bowen type optical pumping are considered in detail. General questions (narrowing of APL spectral lines, the possibility of scattering feedback and ways of measuring the true spectral width of an APL) are considered. Nonlinear optical effects in astrophysical conditions and resonance-enhanced two-photon conditions, in particular, are discussed in the conclusion. (C) 2007 Elsevier B.V. All rights reserved.
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| 9. |
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| 10. |
- Papitto, A., et al.
(författare)
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The INTEGRAL view of the pulsating hard X-ray sky : from accreting and transitional millisecond pulsars to rotation-powered pulsars and magnetars
- 2020
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Ingår i: New astronomy reviews (Print). - : Elsevier BV. - 1387-6473 .- 1872-9630. ; 91
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Tidskriftsartikel (refereegranskat)abstract
- In the last 25 years a new generation of X-ray satellites imparted a significant leap forward in our knowledge of X-ray pulsars. The discovery of accreting and transitional millisecond pulsars proved that disk accretion can spin up a neutron star to a very high rotation speed. The detection of MeV-GeV pulsed emission from a few hundreds of rotation-powered pulsars probed particle acceleration in the outer magnetosphere, or even beyond. Also, a population of two dozens of magnetars has emerged. INTEGRAL played a central role to achieve these results by providing instruments with high temporal resolution up to the hard X-ray/soft, gamma-ray band and a large field of view imager with good angular resolution to spot hard X-ray transients. In this article we review the main contributions by INTEGRAL to our understanding of the pulsating hard X-ray sky, such as the discovery and characterization of several accreting and transitional millisecond pulsars, the generation of the first catalog of hard X-ray/soft gamma-ray rotation-powered pulsars, the detection of polarization in the hard X-ray emission from the Crab pulsar, and the discovery of persistent hard X-ray emission from several magnetars.
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