| 1. |
- Aharonian, F., et al.
(författare)
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Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts
- 2023
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Ingår i: Nature Astronomy. - : Nature Publishing Group. - 2397-3366. ; 7:11, s. 1341-1350
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Tidskriftsartikel (refereegranskat)abstract
- Gamma-ray observations have established energetic isolated pulsars as outstanding particle accelerators and antimatter factories. However, many questions are still open regarding the acceleration and radiation processes involved, as well as the locations where they occur. The radiation spectra of all gamma-ray pulsars observed to date show strong cutoffs or a break above energies of a few gigaelectronvolts. Using the High Energy Stereoscopic System's Cherenkov telescopes, we discovered a radiation component from the Vela pulsar which emerges beyond this generic cutoff and extends up to energies of at least 20 teraelectronvolts. This is an order of magnitude larger than in the case of the Crab pulsar, the only other pulsar detected in the teraelectronvolt energy range. Our results challenge the state-of-the-art models for the high-energy emission of pulsars. Furthermore, they pave the way for investigating other pulsars through their multiteraelectronvolt emission, thereby imposing additional constraints on the acceleration and emission processes in their extreme energy limit. The H.E.S.S. gamma-ray observatory has observed gamma rays with energies of at least 20 TeV from a pulsar, an energy regime that is hard to reconcile with the existing theories of gamma-ray production for such objects.
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| 2. |
- Goobar, Ariel, 1962-, et al.
(författare)
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Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:9, s. 1098-1107
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Tidskriftsartikel (refereegranskat)abstract
- Detecting gravitationally lensed supernovae is among the biggest challenges in astronomy. It involves a combination of two very rare phenomena: catching the transient signal of a stellar explosion in a distant galaxy and observing it through a nearly perfectly aligned foreground galaxy that deflects light towards the observer. Here we describe how high-cadence optical observations with the Zwicky Transient Facility, with its unparalleled large field of view, led to the detection of a multiply imaged type Ia supernova, SN Zwicky, also known as SN 2022qmx. Magnified nearly 25-fold, the system was found thanks to the standard candle nature of type Ia supernovae. High-spatial-resolution imaging with the Keck telescope resolved four images of the supernova with very small angular separation, corresponding to an Einstein radius of only θE = 0.167″ and almost identical arrival times. The small θE and faintness of the lensing galaxy are very unusual, highlighting the importance of supernovae to fully characterize the properties of galaxy-scale gravitational lenses, including the impact of galaxy substructures.
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| 3. |
- Kruk, Sandor, et al.
(författare)
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The impact of satellite trails on Hubble Space Telescope observations
- 2023
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Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 7, s. 262-268
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Tidskriftsartikel (refereegranskat)abstract
- The recent launch of low Earth orbit satellite constellations is creating a growing threat for astronomical observations with ground-based telescopes1–10 that has alarmed the astronomical community 11–16. Observations affected by artificial satellites can become unusable for scientific research, wasting a growing fraction of the research budget on costly infrastructures and mitigation efforts. Here we report the first measurements, to our knowledge, of artificial satellite contamination on observations from a low Earth orbit made with the Hubble Space Telescope. With the help of volunteers on a citizen science project (www.asteroidhunter.org) and a deep learning algorithm, we scanned the archive of Hubble Space Telescope images taken between 2002 and 2021. We find that a fraction of 2.7% of the individual exposures with a typical exposure time of 11 minutes are crossed by satellites and that the fraction of satellite trails in the images increases with time. This fraction depends on the size of the field of view, exposure time, filter used and pointing. With the growing number of artificial satellites currently planned, the fraction of Hubble Space Telescope images crossed by satellites will increase in the next decade and will need further close study and monitoring.
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| 4. |
- Levan, Andrew J., et al.
(författare)
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A long-duration gamma-ray burst of dynamical origin from the nucleus of an ancient galaxy
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:8, s. 976-985
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Tidskriftsartikel (refereegranskat)abstract
- The majority of long-duration (>2 s) gamma-ray bursts (GRBs) arise from the collapse of massive stars, with a small proportion created from the merger of compact objects. Most of these systems form via standard stellar evolution pathways. However, a fraction of GRBs may result from dynamical interactions in dense environments. These channels could also contribute substantially to the samples of compact object mergers detected as gravitational wave sources. Here we report the case of GRB 191019A, a long GRB (a duration of T90 = 64.4 ± 4.5 s), which we pinpoint close (⪅100 pc projected) to the nucleus of an ancient (>1 Gyr old) host galaxy at z = 0.248. The lack of evidence for star formation and deep limits on any supernova emission disfavour a massive star origin. The most likely route for progenitor formation is via dynamical interactions in the dense nucleus of the host. The progenitor, in this case, could be a compact object merger. These may form in dense nuclear clusters or originate in a gaseous disc around the supermassive black hole. Identifying, to the best of our knowledge, a first example of a dynamically produced GRB demonstrates the role that such bursts may have in probing dense environments and constraining dynamical fractions in gravitational wave populations.
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| 5. |
- Lin, Weili, et al.
(författare)
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A superluminous supernova lightened by collisions with pulsational pair-instability shells
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:7, s. 779-789
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Tidskriftsartikel (refereegranskat)abstract
- Superluminous supernovae are among the most energetic stellar explosions in the Universe, but their energy sources remain an open question. Here we present long-term observations of one of the closest examples of the hydrogen-poor superluminous supernovae subclass SLSNe-I, supernova SN 2017egm, revealing the most complicated known luminosity evolution of SLSNe-I. Three distinct post-peak bumps were recorded in its light curve collected at about 100–350 days after maximum brightness, challenging current popular power models such as magnetar, fallback accretion, and interaction between ejecta and a circumstellar shell. However, the complex light curve can be well modelled by successive interactions with multiple circumstellar shells with a total mass of about 6.8–7.7 M⊙. In this scenario, large energy deposition from interaction-induced reverse shocks results in ionization of neutral oxygen in the supernova ejecta and hence a much lower nebular-phase line ratio of [O I] λ6,300/([Ca II] + [O II]) λ7,300 (~0.2) compared with that derived for other superluminous and normal stripped-envelope supernovae. The pre-existing multiple shells indicate that the progenitor of SN 2017egm experienced pulsational mass ejections triggered by pair instability within 2 years before explosion, in robust agreement with theoretical predictions for a pre-pulsation helium-core mass of 48–51 M⊙.
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| 6. |
- Pasham, Dheeraj R., et al.
(författare)
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The Birth of a Relativistic Jet Following the Disruption of a Star by a Cosmological Black Hole
- 2023
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 7:1, s. 88-104
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Tidskriftsartikel (refereegranskat)abstract
- A black hole can launch a powerful relativistic jet after it tidally disrupts a star. If this jet fortuitously aligns with our line of sight, the overall brightness is Doppler boosted by several orders of magnitude. Consequently, such on-axis relativistic tidal disruption events have the potential to unveil cosmological (redshift z > 1) quiescent black holes and are ideal test beds for understanding the radiative mechanisms operating in super-Eddington jets. Here we present multiwavelength (X-ray, UV, optical and radio) observations of the optically discovered transient AT 2022cmc at z = 1.193. Its unusual X-ray properties, including a peak observed luminosity of ≳1048 erg s−1, systematic variability on timescales as short as 1,000 s and overall duration lasting more than 30 days in the rest frame, are traits associated with relativistic tidal disruption events. The X-ray to radio spectral energy distributions spanning 5–50 days after discovery can be explained as synchrotron emission from a relativistic jet (radio), synchrotron self-Compton (X-rays) and thermal emission similar to that seen in low-redshift tidal disruption events (UV/optical). Our modelling implies a beamed, highly relativistic jet akin to blazars but requires extreme matter domination (that is, a high ratio of electron-to-magnetic-field energy densities in the jet) and challenges our theoretical understanding of jets.
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| 7. |
- Sawala, Till, et al.
(författare)
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The Milky Way’s plane of satellites is consistent with ΛCDM
- 2023
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 7:4, s. 481-491
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Tidskriftsartikel (refereegranskat)abstract
- The Milky Way is surrounded by 11 ‘classical’ satellite galaxies in a remarkable configuration: a thin plane that is possibly rotationally supported. Such a structure is thought to be highly unlikely to arise in the standard (ΛCDM) cosmological model (Λ cold dark matter model, where Λ is the cosmological constant). While other apparent discrepancies between predictions and observations of Milky Way satellite galaxies may be explained either through baryonic effects or by invoking alternative forms of dark matter particles, there is no known mechanism for making rotating satellite planes within the dispersion-supported dark matter haloes predicted to surround galaxies such as the Milky Way. This is the so-called ‘plane of satellites problem’, which challenges not only the ΛCDM model but the entire concept of dark matter. Here we show that the reportedly exceptional anisotropy of the Milky Way satellites is explained, in large part, by their lopsided radial distribution combined with the temporary conjunction of the two most distant satellites, Leo I and Leo II. Using Gaia proper motions, we show that the orbital pole alignment is much more common than previously reported, and reveal the plane of satellites to be transient rather than rotationally supported. Comparing with new simulations, where such short-lived planes are common, we find the Milky Way satellites to be compatible with standard model expectations.
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| 8. |
- Schneider, Mike D., et al.
(författare)
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Cosmology and empire
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:4, s. 368-370
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- What is the link between the discovery of the relativistic expanding Universe and British imperialism? A public panel debate in the early days of relativistic cosmology shows how fundamental scientific research, whether there are obvious political stakeholders (like biosecurity and climate) or not, runs real-time risks of being repurposed for political ends.
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| 9. |
- Serjeant, Stephen, et al.
(författare)
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Objects in JWST’s mirrors are closer than they appear
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:10, s. 1143-1144
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- JWST has revealed the most distant galaxies known, but photometric estimates of their redshifts are likely to be overly generous, owing to a statistical effect identified by Sir Arthur Eddington.
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| 10. |
- Snelders, M. P., et al.
(författare)
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Detection of ultra-fast radio bursts from FRB 20121102A
- 2023
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Ingår i: Nature Astronomy. - 2397-3366. ; 7:12, s. 1486-1496
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Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are extragalactic transient flashes of radio waves with typical durations of milliseconds. FRBs have been shown, however, to present a wide range of timescales: some show sub-microsecond sub-bursts while others last up to a few seconds. Probing FRBs on a range of timescales is crucial for understanding their emission physics, how to detect them effectively and how to maximize their utility as astrophysical probes. FRB 20121102A is the first known repeating FRB source. Here we show that FRB 20121102A produces isolated microsecond-duration bursts with durations less than one-tenth the duration of other currently known FRBs. The polarimetric properties of these microsecond-duration bursts resemble those of the longer-lasting bursts, suggesting a common emission mechanism producing FRBs with durations spanning three orders of magnitude. In detecting and characterizing these microsecond-duration bursts, we show that there exists a population of ultra-fast radio bursts that current wide-field FRB searches are missing due to insufficient time resolution. These results indicate that FRBs occur more frequently and with greater diversity than initially thought. This could also influence our understanding of energy, wait time and burst rate distributions.
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