| 1. |
- Ahumada, T., et al.
(författare)
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Discovery and confirmation of the shortest gamma-ray burst from a collapsar
- 2021
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Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 5:9, s. 917-927
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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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| 2. |
- Ajello, M., et al.
(författare)
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High-energy emission from a magnetar giant flare in the Sculptor galaxy
- 2021
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Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 5:4, s. 385-391
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Tidskriftsartikel (refereegranskat)abstract
- Magnetars are the most highly magnetized neutron stars in the cosmos (with magnetic field 1013–1015 G). Giant flares from magnetars are rare, short-duration (about 0.1 s) bursts of hard X-rays and soft γ rays1,2. 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 γ rays from 19 s until 284 s after the initial detection of a signal in the megaelectronvolt (MeV) band. Our analysis shows that these γ rays are spatially associated with the nearby (3.5 megaparsecs) Sculptor galaxy and are unlikely to originate from a cosmological γ-ray burst. Thus, we infer that the γ 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 γ 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 γ-ray bursts.
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| 3. |
- Augier, Pierre, et al.
(författare)
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Reducing the ecological impact of computing through education and Python compilers
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5:4, s. 334-335
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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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| 4. |
- Delrez, Laetitia, et al.
(författare)
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Transit detection of the long-period volatile-rich super-Earth nu(2) Lupi d with CHEOPS
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; :5, s. 775-787
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Tidskriftsartikel (refereegranskat)abstract
- Exoplanets transiting bright nearby stars are key objects for advancing our knowledge of planetary formation and evolution. The wealth of photons from the host star gives detailed access to the atmospheric, interior and orbital properties of the planetary companions. nu(2) Lupi (HD 136352) is a naked-eye (V = 5.78) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6 and 107.6 d via radial-velocity monitoring(1). The two inner planets (b and c) were recently found to transit(2), prompting a photometric follow-up by the brand new Characterising Exoplanets Satellite (CHEOPS). Here, we report that the outer planet d is also transiting, and measure its radius and mass to be 2.56 +/- 0.09 R-circle plus and 8.82 +/- 0.94 M-circle plus, respectively. With its bright Sun-like star, long period and mild irradiation (similar to 5.7 times the irradiation of Earth), nu(2) Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. We refine the properties of all three planets: planet b probably has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the nu(2) Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.
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| 5. |
- Franco, Maximilian, et al.
(författare)
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The ramp-up of interstellar medium enrichment at z > 4
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5, s. 1240-1246
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Tidskriftsartikel (refereegranskat)abstract
- Fluorine is one of the most interesting elements for nuclear and stellar astrophysics1,2. Fluorine abundance was first measured for stars other than the Sun in 19921, then for a handful of metal-poor stars3, which are likely to have formed in the early Universe. The main production sites of fluorine are under debate and include asymptotic giant branch stars, the ν-process in core-collapse supernovae, and Wolf–Rayet stars4,5,6,7,8,9,10. Due to the difference in the mass and lifetime of progenitor stars, high-redshift observations of fluorine can help constrain the mechanism of fluorine production in massive galaxies. Here, we report the detection of HF (signal-to-noise ratio of 8) in absorption in a gravitationally lensed dusty star-forming galaxy at redshift z = 4.4 with NHF/NH2NH2 as high as ~2 × 10−9, indicating a very quick ramp-up of the chemical enrichment in this high-z galaxy. At z = 4.4, asymptotic giant branch stars of a few solar masses are very unlikely to dominate the enrichment. Instead, we show that Wolf–Rayet stars are required to produce the observed fluorine abundance at this time, with other production mechanisms becoming important at later times. These observations therefore provide an insight into the underlying processes driving the ramp-up phase of chemical enrichment alongside rapid stellar mass assembly in a young massive galaxy.
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| 6. |
- Janssen, Michael, et al.
(författare)
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Event Horizon Telescope observations of the jet launching and collimation in Centaurus A
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5:10, s. 1017-1028
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Tidskriftsartikel (refereegranskat)abstract
- Very-long-baseline interferometry (VLBI) observations of active galactic nuclei at millimetre wavelengths have the power to reveal the launching and initial collimation region of extragalactic radio jets, down to 10–100 gravitational radii (rg ≡ GM/c2) scales in nearby sources1. Centaurus A is the closest radio-loud source to Earth2. It bridges the gap in mass and accretion rate between the supermassive black holes (SMBHs) in Messier 87 and our Galactic Centre. A large southern declination of −43° has, however, prevented VLBI imaging of Centaurus A below a wavelength of 1 cm thus far. Here we show the millimetre VLBI image of the source, which we obtained with the Event Horizon Telescope at 228 GHz. Compared with previous observations3, we image the jet of Centaurus A at a tenfold higher frequency and sixteen times sharper resolution and thereby probe sub-lightday structures. We reveal a highly collimated, asymmetrically edge-brightened jet as well as the fainter counterjet. We find that the source structure of Centaurus A resembles the jet in Messier 87 on ~500 rg scales remarkably well. Furthermore, we identify the location of Centaurus A’s SMBH with respect to its resolved jet core at a wavelength of 1.3 mm and conclude that the source’s event horizon shadow4 should be visible at terahertz frequencies. This location further supports the universal scale invariance of black holes over a wide range of masses5,6.
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| 7. |
- Kirsten, Franz, 1983, et al.
(författare)
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Detection of two bright radio bursts from magnetar SGR 1935 + 2154
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5:4, s. 414-422
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Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts are millisecond-duration, bright radio signals (fluence 0.1-100 Jy ms) emitted from extragalactic sources of unknown physical origin. The recent CHIME/FRB and STARE2 detection of an extremely bright (fluence similar to MJy ms) radio burst from the Galactic magnetar SGR 1935+2154 supports the hypothesis that (at least some) fast radio bursts are emitted by magnetars at cosmological distances. In follow-up observations totalling 522.7 h on source, we detect two bright radio bursts with fluences of 112 +/- 22 Jy ms and 24 +/- 5 Jy ms, respectively. Both bursts appear to be affected by interstellar scattering and we measure significant linear and circular polarization for the fainter burst. The bursts are separated in time by similar to 1.4 s, suggesting a non-Poissonian, clustered emission process-similar to those seen in some repeating fast radio bursts. Together with the burst reported by CHIME/FRB and STARE2, as well as a much fainter burst seen by FAST (fluence 60 mJy ms), our observations demonstrate that SGR 1935+2154 can produce bursts with apparent energies spanning roughly seven orders of magnitude, and that the burst rate is comparable across this range. This raises the question of whether these four bursts arise from similar physical processes, and whether the fast radio burst population distribution extends to very low energies (similar to 10(30) erg, isotropic equivalent).
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| 8. |
- Nimmo, K., et al.
(författare)
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Highly polarized microstructure from the repeating FRB 20180916B
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5:6, s. 594-603
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Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are bright, coherent, short-duration radio transients of as-yet unknown extragalactic origin. FRBs exhibit a variety of spectral, temporal and polarimetric properties that can unveil clues into their emission physics and propagation effects in the local medium. Here, we present the high-time-resolution (down to 1 mu s) polarimetric properties of four 1.7 GHz bursts from the repeating FRB 20180916B, which were detected in voltage data during observations with the European Very Long Baseline Interferometry Network. We observe a range of emission timescales that spans three orders of magnitude, with the shortest component width reaching 3-4 mu s (below which we are limited by scattering). We demonstrate that all four bursts are highly linearly polarized (greater than or similar to 80%), show no evidence of significant circular polarization (less than or similar to 15%), and exhibit a constant polarization position angle (PPA) during and between bursts. On short timescales (less than or similar to 100 mu s), however, there appear to be subtle PPA variations (of a few degrees) across the burst profiles. These observational results are most naturally explained in an FRB model in which the emission is magnetospheric in origin, in contrast to models in which the emission originates at larger distances in a relativistic shock. High-time-resolution observations of the repeating fast radio burst source FRB 20180916B reveal changes to the polarization properties of the emission on timescales of a few microseconds, indicating an origin in the source magnetosphere.
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| 9. |
- Roth, Lorenz, et al.
(författare)
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A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations
- 2021
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Ingår i: Nature Astronomy. - : Springer Nature. - 2397-3366. ; 5:10, s. 1043-1051
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Tidskriftsartikel (refereegranskat)abstract
- Ganymede’s atmosphere is produced by charged particle sputtering and sublimation of its icy surface. Previous far-ultraviolet observations of the O i 1,356 Å and O i 1,304 Å oxygen emissions were used to infer sputtered molecular oxygen (O2) as an atmospheric constituent, but an expected sublimated water (H2O) component remained undetected. Here we present an analysis of high-sensitivity spectra and spectral images acquired by the Hubble Space Telescope revealing H2O in Ganymede’s atmosphere. The relative intensity of the oxygen emissions requires contributions from the dissociative excitation of water vapour, indicating that H2O is more abundant than O2 around the subsolar point. Away from the subsolar region, the emissions are consistent with a pure O2 atmosphere. Eclipse observations constrain atomic oxygen to be at least two orders of magnitude less abundant than these other species. The higher H2O/O2 ratio above the warmer trailing hemisphere compared with the colder leading hemisphere, the spatial concentration in the subsolar region and the estimated abundance of ~1015 molecules of H2O per cm2 are consistent with sublimation of the icy surface as source.
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| 10. |
- Ryde, Nils, et al.
(författare)
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Observing early stellar nucleosynthesis
- 2021
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 5:12, s. 1212-1213
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Tidskriftsartikel (refereegranskat)
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