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Sökning: L773:2397 3366

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1.
  • Abdalla, H., et al. (författare)
  • Resolving the Crab pulsar wind nebula at teraelectronvolt energies
  • 2020
  • Ingår i: Nature Astronomy. - : Nature Publishing Group. - 2397-3366. ; 4:2, s. 167-173
  • Tidskriftsartikel (refereegranskat)abstract
    • An angular extension at gamma-ray energies of 52 arcseconds is detected for the Crab nebula, revealing the emission region of the highest-energy gamma rays; simulations of the electromagnetic emission provide a non-trivial test of our understanding of particle acceleration in the Crab nebula. The Crab nebula is one of the most-studied cosmic particle accelerators, shining brightly across the entire electromagnetic spectrum up to very-high-energy gamma rays(1,2). It is known from observations in the radio to gamma-ray part of the spectrum that the nebula is powered by a pulsar, which converts most of its rotational energy losses into a highly relativistic outflow. This outflow powers a pulsar wind nebula, a region of up to ten light-years across, filled with relativistic electrons and positrons. These particles emit synchrotron photons in the ambient magnetic field and produce very-high-energy gamma rays by Compton up-scattering of ambient low-energy photons. Although the synchrotron morphology of the nebula is well established, it has not been known from which region the very-high-energy gamma rays are emitted(3-8). Here we report that the Crab nebula has an angular extension at gamma-ray energies of 52 arcseconds (assuming a Gaussian source width), much larger than at X-ray energies. This result closes a gap in the multi-wavelength coverage of the nebula, revealing the emission region of the highest-energy gamma rays. These gamma rays enable us to probe a previously inaccessible electron and positron energy range. We find that simulations of the electromagnetic emission reproduce our measurement, providing a non-trivial test of our understanding of particle acceleration in the Crab nebula.
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2.
  • Ahumada, T., et al. (författare)
  • Discovery and confirmation of the shortest gamma-ray burst from a collapsar
  • 2021
  • Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 5:9, s. 917-927
  • Tidskriftsartikel (refereegranskat)abstract
    • Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the Universe. The duration and hardness distribution of GRBs has two clusters1, now understood to reflect (at least) two different progenitors2. Short-hard GRBs (SGRBs; T90 < 2 s) arise from compact binary mergers, and long-soft GRBs (LGRBs; T90 > 2 s) have been attributed to the collapse of peculiar massive stars (collapsars)3. The discovery of SN 1998bw/GRB 980425 (ref. 4) marked the first association of an LGRB with a collapsar, and AT 2017gfo (ref. 5)/GRB 170817A/GW170817 (ref. 6) marked the first association of an SGRB with a binary neutron star merger, which also produced a gravitational wave. Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi satellite and the Interplanetary Network localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova, but which is consistent with being the supernova. Although the GRB duration is short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirm a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets.
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3.
  • Ajello, M., et al. (författare)
  • High-energy emission from a magnetar giant flare in the Sculptor galaxy
  • 2021
  • Ingår i: Nature Astronomy. - 2397-3366. ; 5:4, s. 385-391
  • Tidskriftsartikel (refereegranskat)abstract
    • Magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 10(13)-10(15) G). Giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard X-rays and soft gamma rays(1,2). Owing to the limited sensitivity and energy coverage of previous telescopes, no magnetar giant flare has been detected at gigaelectronvolt (GeV) energies. Here, we report the discovery of GeV emission from a magnetar giant flare on 15 April 2020 (refs. (3,4) and A. J. Castro-Tirado et al., manuscript in preparation). The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope detected GeV gamma rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (MeV) band. Our analysis shows that these gamma rays are spatially associated with the nearby (3.5 megaparsecs) Sculptor galaxy and are unlikely to originate from a cosmological gamma-ray burst. Thus, we infer that the gamma rays originated with the magnetar giant flare in Sculptor. We suggest that the GeV signal is generated by an ultra-relativistic outflow that first radiates the prompt MeV-band photons, and then deposits its energy far from the stellar magnetosphere. After a propagation delay, the outflow interacts with environmental gas and produces shock waves that accelerate electrons to very high energies; these electrons then emit GeV gamma rays as optically thin synchrotron radiation. This observation implies that a relativistic outflow is associated with the magnetar giant flare, and suggests the possibility that magnetars can power some short gamma-ray bursts.
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4.
  • Anand, S., et al. (författare)
  • Optical follow-up of the neutron star–black hole mergers S200105ae and S200115j
  • 2020
  • Ingår i: Nature Astronomy. - : Nature Research. - 2397-3366.
  • Tidskriftsartikel (refereegranskat)abstract
    • LIGO and Virgo’s third observing run revealed the first neutron star–black hole (NSBH) merger candidates in gravitational waves. These events are predicted to synthesize r-process elements1,2 creating optical/near-infrared ‘kilonova’ emission. The joint gravitational wave and electromagnetic detection of an NSBH merger could be used to constrain the equation of state of dense nuclear matter3, and independently measure the local expansion rate of the Universe4. Here, we present the optical follow-up and analysis of two of the only three high-significance NSBH merger candidates detected to date, S200105ae and S200115j, with the Zwicky Transient Facility5. The Zwicky Transient Facility observed ~48% of S200105ae and ~22% of S200115j’s localization probabilities, with observations sensitive to kilonovae brighter than −17.5 mag fading at 0.5 mag d−1 in the g- and r-bands; extensive searches and systematic follow-up of candidates did not yield a viable counterpart. We present state-of-the-art kilonova models tailored to NSBH systems that place constraints on the ejecta properties of these NSBH mergers. We show that with observed depths of apparent magnitude ~22 mag, attainable in metre-class, wide-field-of-view survey instruments, strong constraints on ejecta mass are possible, with the potential to rule out low mass ratios, high black hole spins and large neutron star radii.
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5.
  • Anderson, P., et al. (författare)
  • The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor
  • 2018
  • Ingår i: Nature Astronomy. - 2397-3366. ; 2:7, s. 574-579
  • Tidskriftsartikel (refereegranskat)abstract
    • Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae(1). However, while such stars are observed with masses > 25 M-circle dot (ref. (2)), detections of > 18 M-circle dot progenitors remain elusive(1). Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of <= 0.1 Z(circle dot) from comparison to photospheric-phase spectral models(3), and a zero-age main-sequence mass of 17-25 M-circle dot through comparison to nebular-phase spectral models(4,5). SN 2015bs displays a normal 'plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high-mass progenitor for a 'normal' type II supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors.
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6.
  • Augier, Pierre, et al. (författare)
  • Reducing the ecological impact of computing through education and Python compilers
  • 2021
  • Ingår i: Nature Astronomy. - 2397-3366. ; 5:4, s. 334-335
  • Tidskriftsartikel (refereegranskat)abstract
    • We read with interest the Comment by Portegies Zwart on the ecological impact of high-performance computing in astrophysics. We fully agree with its take-home message: scientists should be mindful of their carbon footprint. One of the proposed solutions, however, is to avoid the Python programming language. We contend that this would be counterproductive and that scientific programs written in Python can be efficient and energy-friendly. We argue that human factors, such as education, and the advancement of compiler technology are much more important than choice of language.
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7.
  • Battersby, C., et al. (författare)
  • The Origins Space Telescope
  • 2018
  • Ingår i: Nature Astronomy. - 2397-3366. ; 2:8, s. 596-599
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • The Origins Space Telescope, one of four large Mission Concept Studies sponsored by NASA for review in the 2020 US Astrophysics Decadal Survey, will open unprecedented discovery space in the infrared, unveiling our cosmic origins.
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8.
  • Bulla, Mattia, et al. (författare)
  • The origin of polarization in kilonovae and the case of the gravitational-wave counterpart AT 2017gfo
  • 2019
  • Ingår i: Nature Astronomy. - 2397-3366. ; 3:1, s. 99-106
  • Tidskriftsartikel (refereegranskat)abstract
    • The gravitational-wave event GW 170817 was generated by the coalescence of two neutron stars and produced an electromagnetic transient, labelled AT 2017gfo, that was the target of a massive observational campaign. Polarimetry is a powerful diagnostic tool for probing the geometry and emission processes of unresolved sources, and the observed linear polarization for this event was consistent with being mostly induced by intervening dust, suggesting that the intrinsic emission was weakly polarized (P < 0.4-0.5%). Here we present a detailed analysis of the linear polarization expected from a merging neutron-star binary system by means of 3D Monte Carlo radiative transfer simulations assuming a range of possible configurations, wavelengths, epochs and viewing angles. We find that polarization originates from the non-homogeneous opacity distribution within the ejecta and can reach levels of 1% at early times (one to two days after the merger) and in the optical R band. Smaller polarization signals are expected at later epochs and different wavelengths. From the viewing-angle dependence of the polarimetric signal, we constrain the observer orientation of AT 2017gfo to within about 65 degrees from the polar direction. The detection of non-zero polarization in future events will unambiguously reveal the presence of a lanthanide-free ejecta component and unveil its spatial and angular distribution.
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9.
  • Chauvin, Maxime, et al. (författare)
  • Accretion geometry of the black-hole binary Cygnus X-1 from X-ray polarimetry
  • 2018
  • Ingår i: Nature Astronomy. - : Nature Publishing Group. - 2397-3366. ; 2:8, s. 652-655
  • Tidskriftsartikel (refereegranskat)abstract
    • Black hole binary (BHB) systems comprise a stellar-mass black hole and a closely orbiting companion star. Matter is transferred from the companion to the black hole, forming an accretion disk, corona and jet structures. The resulting release of gravitational energy leads to the emission of X-rays1. The radiation is affected by special/general relativistic effects, and can serve as a probe for the properties of the black hole and surrounding environment, if the accretion geometry is properly identified. Two competing models describe the disk–corona geometry for the hard spectral state of BHBs, based on spectral and timing measurements2,3. Measuring the polarization of hard X-rays reflected from the disk allows the geometry to be determined. The extent of the corona differs between the two models, affecting the strength of the relativistic effects (such as enhancement of the polarization fraction and rotation of the polarization angle). Here, we report observational results on the linear polarization of hard X-ray emission (19–181 keV) from a BHB, Cygnus X-14, in the hard state. The low polarization fraction, <8.6% (upper limit at a 90% confidence level), and the alignment of the polarization angle with the jet axis show that the dominant emission is not influenced by strong gravity. When considered together with existing spectral and timing data, our result reveals that the accretion corona is either an extended structure, or is located far from the black hole in the hard state of Cygnus X-1.
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10.
  • Decin, L., et al. (författare)
  • Reduction of the maximum mass-loss rate of OH/IR stars due to unnoticed binary interaction
  • 2019
  • Ingår i: Nature Astronomy. - 2397-3366. ; 3:5, s. 408-415
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • © 2019, The Author(s), under exclusive licence to Springer Nature Limited. In 1981, the idea of a superwind that ends the life of cool giant stars was proposed 1 . Extreme oxygen-rich giants, OH/IR stars, develop superwinds with the highest mass-loss rates known so far, up to a few 10 −4 solar masses (M ⊙ ) per year 2–12 , informing our understanding of the maximum mass-loss rate achieved during the asymptotic giant branch (AGB) phase. A conundrum arises whereby the observationally determined duration of the superwind phase is too short for these stars to lose enough mass to become white dwarfs 2–4,6,8–10 . Here we report on the detection of spiral structures around two cornerstone extreme OH/IR stars, OH 26.5 + 0.6 and OH 30.1 − 0.7, thereby identifying them as wide binary systems. Hydrodynamic simulations show that the companion’s gravitational attraction creates an equatorial density enhancement mimicking a short, extreme superwind phase, thereby solving the decades-old conundrum. This discovery restricts the maximum mass-loss rate of AGB stars to around the single-scattering radiation pressure limit of a few 10 −5 M ⊙ yr −1 . This has crucial implications for nucleosynthetic yields, planet survival and the wind-driving mechanism.
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  • Resultat 1-10 av 56
  • [1]23456Nästa

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