| 1. |
- Agudo, I., et al.
(författare)
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Panning for gold, but finding helium: Discovery of the ultra-stripped supernova SN 2019wxt from gravitational-wave follow-up observations
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 675
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from multi-wavelength observations of a transient discovered during an intensive follow-up campaign of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN 2019wxt, a young transient in a galaxy whose sky position (in the 80% GW contour) and distance (∼150 Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transienta's tightly constrained age, its relatively faint peak magnitude (Mi ∼ -16.7 mag), and the r-band decline rate of ∼1 mag per 5 days appeared suggestive of a compact binary merger. However, SN 2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of only ∼0.1 M·, with 56Ni comprising ∼20% of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitor channels that could give rise to the observed properties of SN 2019wxt and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling genuine electromagnetic counterparts to GW events from transients such as SN 2019wxt soon after discovery is challenging: in a bid to characterise this level of contamination, we estimated the rate of events with a volumetric rate density comparable to that of SN 2019wxt and found that around one such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500 Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns.
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| 2. |
- Paraschos, Georgios Filippos, et al.
(författare)
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Ordered magnetic fields around the 3C 84 central black hole
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Context . 3C 84 is a nearby radio source with a complex total intensity structure, showing linear polarisation and spectral patterns. A detailed investigation of the central engine region necessitates the use of very-long-baseline interferometry (VLBI) above the hitherto available maximum frequency of 86 GHz. Aims. Using ultrahigh resolution VLBI observations at the currently highest available frequency of 228 GHz, we aim to perform a direct detection of compact structures and understand the physical conditions in the compact region of 3C 84. Methods . We used Event Horizon Telescope (EHT) 228 GHz observations and, given the limited (u, v)-coverage, applied geometric model fitting to the data. Furthermore, we employed quasi-simultaneously observed, ancillary multi-frequency VLBI data for the source in order to carry out a comprehensive analysis of the core structure. Results . We report the detection of a highly ordered, strong magnetic field around the central, supermassive black hole of 3C 84. The brightness temperature analysis suggests that the system is in equipartition. We also determined a turnover frequency of νm = (113 ± 4) GHz, a corresponding synchrotron self-absorbed magnetic field of BSSA = (2.9 ± 1.6) G, and an equipartition magnetic field of Beq = (5.2 ± 0.6) G. Three components are resolved with the highest fractional polarisation detected for this object (mnet = (17.0 ± 3.9)%). The positions of the components are compatible with those seen in low-frequency VLBI observations since 2017-2018. We report a steeply negative slope of the spectrum at 228 GHz. We used these findings to test existing models of jet formation, propagation, and Faraday rotation in 3C 84. Conclusions . The findings of our investigation into different flow geometries and black hole spins support an advection-dominated accretion flow in a magnetically arrested state around a rapidly rotating supermassive black hole as a model of the jet-launching system in the core of 3C 84. However, systematic uncertainties due to the limited (u, v)-coverage, however, cannot be ignored. Our upcoming work using new EHT data, which offer full imaging capabilities, will shed more light on the compact region of 3C 84.
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| 3. |
- Heald, G., et al.
(författare)
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Magnetism science with the square kilometre array
- 2020
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Ingår i: Galaxies. - : MDPI AG. - 2075-4434. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will answer fundamental questions about the origin, evolution, properties, and influence of magnetic fields throughout the Universe. Magnetic fields can illuminate and influence phenomena as diverse as star formation, galactic dynamics, fast radio bursts, active galactic nuclei, large-scale structure, and dark matter annihilation. Preparations for the SKA are swiftly continuing worldwide, and the community is making tremendous observational progress in the field of cosmic magnetism using data from a powerful international suite of SKA pathfinder and precursor telescopes. In this contribution, we revisit community plans for magnetism research using the SKA, in light of these recent rapid developments. We focus in particular on the impact that new radio telescope instrumentation is generating, thus advancing our understanding of key SKA magnetism science areas, as well as the new techniques that are required for processing and interpreting the data. We discuss these recent developments in the context of the ultimate scientific goals for the SKA era.
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| 4. |
- Ghirlanda, G., et al.
(författare)
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Compact radio emission indicates a structured jet was produced by a binary neutron star merger
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 363:6430, s. 968-971
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Tidskriftsartikel (refereegranskat)abstract
- The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli-arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.
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| 5. |
- Kim, J. Y., et al.
(författare)
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Spatially resolved origin of millimeter-wave linear polarization in the nuclear region of 3C 84
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
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Tidskriftsartikel (refereegranskat)abstract
- We report results from a deep polarization imaging of the nearby radio galaxy 3C 84 (NGC 1275). The source was observed with the Global Millimeter VLBI Array (GMVA) at 86 GHz at an ultrahigh angular resolution of 50 μas (corresponding to ∼200Rs). We also add complementary multiwavelength data from the Very Long Baseline Array (VLBA; 15 and 43 GHz) and from the Atacama Large Millimeter/submillimeter Array (ALMA; 97.5, 233.0 and 343.5 GHz). At 86 GHz, we measured a fractional linear polarization of ∼2% in the VLBI core region. The polarization morphology suggests that the emission is associated with an underlying limb-brightened jet. The fractional linear polarization is lower at 43 and 15 GHz (∼0.3-0.7% and <0.1%, respectively). This suggests an increasing linear polarization degree toward shorter wavelengths on VLBI scales. We also obtain a large rotation measure (RM) of ∼10 5-6 rad m 2 in the core at 43 GHz. Moreover, the VLBA 43 GHz observations show a variable RM in the VLBI core region during a small flare in 2015. Faraday depolarization and Faraday conversion in an inhomogeneous and mildly relativistic plasma could explain the observed linear polarization characteristics and the previously measured frequency dependence of the circular polarization. Our Faraday depolarization modeling suggests that the RM most likely originates from an external screen with a highly uniform RM distribution. To explain the large RM value, the uniform RM distribution and the RM variability, we suggest that the Faraday rotation is caused by a boundary layer in a transversely stratified jet. Based on the RM and the synchrotron spectrum of the core, we provide an estimate for the magnetic field strength and the electron density of the jet plasma.
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| 6. |
- Marti-Vidal, Ivan, 1980, et al.
(författare)
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ALMA full polarization observations of PKS 1830-211 during its record-breaking flare of 2019
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 638
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Tidskriftsartikel (refereegranskat)abstract
- We report Atacama Large Millimeter Array (ALMA) Band 6 full-polarization observations of the lensed blazar PKS 1830-211 during its record-breaking radio and gamma-ray flare in the spring of 2019. The observations were taken close to the peak of the gamma activity and show a clear difference in polarization state between the two time-delayed images. The leading image has a fractional polarization about three times lower than the trailing image, implying that significant depolarization occurred during the flare. In addition, we observe clear intra-hour variability of the polarization properties between the two lensed images, with a quasi-linear increase in the differential electric-vector position angle at a rate of about two degrees per hour, associated with changes in the relative fractional polarization of ∼10%. This variability, combined with the lower polarization close to the peak of gamma activity, is in agreement with models of magnetic turbulence to explain polarization variability in blazar jets. Finally, the comparison of results from the full and differential polarization analysis confirms that the differential polarization technique (Martí-Vidal et al. 2016, A&A, 593, A61) can provide useful information on the polarization state of sources like gravitationally lensed radio-loud quasars.
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| 7. |
- Huang, Ko Yun, et al.
(författare)
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Mapping Circumstellar Magnetic Fields of Late-type Evolved Stars with the Goldreich-Kylafis Effect: CARMA Observations at λ1.3 mm of R Crt and R Leo
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 899:2
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Tidskriftsartikel (refereegranskat)abstract
- Mapping magnetic fields is the key to resolving the unclear physical picture of circumstellar magnetic fields in late-type evolved stars. Observations of linearly polarized emission from thermal molecular line transitions due to the Goldreich-Kylafis (G-K) effect provide valuable insights into the magnetic field geometry in these sources that are complementary to other key studies. In this paper, we present the detection of spectral-line polarization from both the thermal J = 2-1 CO line and the v = 1, J = 5-4 SiO maser line toward two thermal-pulsating asymptotic giant branch stars, R Crt and R Leo. The observed fractional linear polarization in the CO emission is measured as m l ∼ 3.1% and m l ∼ 9.7% for R Crt and R Leo, respectively. A circumstellar envelope (CSE) model profile and the associated parameters are estimated and used as input to a more detailed modeling of the predicted linear polarization expected from the G-K effect. The observed thermal line polarization level is consistent with the predicted results from the G-K model for R Crt; additional effects need to be considered for R Leo.
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| 8. |
- Molina, S. N., et al.
(författare)
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Evidence of internal rotation and a helical magnetic field in the jet of the quasar NRAO 150
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- The source NRAO 150 is a very prominent millimeter to radio emitting quasar at redshift z = 1.52 for which previous millimeter VLBI observations revealed a fast counterclockwise rotation of the innermost regions of the jet. Here we present new polarimetric multi-epoch VLBI-imaging observations of NRAO 150 performed at 8, 15, 22, 43, and 86 GHz with the Very Long Baseline Array (VLBA), and the Global Millimeter VLBI Array (GMVA) between 2006 and 2010. All new and previous observational evidence - i.e., spectral index maps, multi-epoch image cross-correlation, and low level of linear polarization degree in optically thin regions - are consistent with an interpretation of the source behavior where the jet is seen at an extremely small angle to the line of sight, and the high frequency emitting regions in NRAO 150 rotate at high speeds on the plane of the sky with respect to a reference point that does not need to be related to any particularly prominent jet feature. The observed polarization angle distribution at 22, 43, and 86 GHz during observing epochs with high polarization degree suggests that we have detected the toroidal component of the magnetic field threading the innermost jet plasma regions. This is also consistent with the lower degree of polarization detected at progressively poorer angular resolutions, where the integrated polarization intensity produced by the toroidal field is explained by polarization cancellation inside the observing beam. All this evidence is fully consistent with a kinematic scenario where the main kinematic and polarization properties of the 43 GHz emitting structure of NRAO 150 are explained by the internal rotation of such emission regions around the jet axis when the jet is seen almost face on. A simplified model developed to fit helical trajectories to the observed kinematics of the 43GHz features fully supports this hypothesis. This explains the kinematics of the innermost regions of the jet in NRAO 150 in terms of internal jet rotation.
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| 9. |
- Schulz, R., et al.
(författare)
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Sub-milliarcsecond imaging of a bright flare and ejection event in the extragalactic jet 3C 111
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 644:December 2020
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Tidskriftsartikel (refereegranskat)abstract
- Context Flares in radio-loud active galactic nuclei are thought to be associated with the injection of fresh plasma into the compact jet base. Such flares are usually strongest and appear earlier at shorter radio wavelengths. Hence, very long baseline interferometry (VLBI) at millimeter(mm)-wavelengths is the best-suited technique for studying the earliest structural changes of compact jets associated with emission flares. Aims We study the morphological changes of the parsec-scale jet in the nearby (z = 0.049) γ-ray bright radio galaxy 3C 111 following a flare that developed into a major radio outburst in 2007. Methods We analyse three successive observations of 3C 111 at 86 GHz with the Global mm-VLBI Array (GMVA) between 2007 and 2008 which yield a very high angular resolution of ∼45 μas. In addition, we make use of single-dish radio flux density measurements from the F-GAMMA and POLAMI programmes, archival single-dish and VLBI data. Results We resolve the flare into multiple plasma components with a distinct morphology resembling a bend in an otherwise remarkably straight jet. The flare-associated features move with apparent velocities of ∼4.0c to ∼4.5c and can be traced also at lower frequencies in later epochs. Near the base of the jet, we find two bright features with high brightness temperatures up to ∼1011 K, which we associate with the core and a stationary feature in the jet. Conclusions The flare led to multiple new jet components indicative of a dynamic modulation during the ejection. We interpret the bend-like feature as a direct result of the outburst which makes it possible to trace the transverse structure of the jet. In this scenario, the components follow different paths in the jet stream consistent with expectations for a spine-sheath structure, which is not seen during intermediate levels of activity. The possibility of coordinated multiwavelength observations during a future bright radio flare in 3C 111 makes this source an excellent target for probing the radio-γ-ray connection.
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| 10. |
- Zamora-Ros, Raul, et al.
(författare)
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Dietary polyphenol intake in europe : The european prospective investigation into cancer and nutrition (EPIC) study
- 2016
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Ingår i: European Journal of Nutrition. - : Springer Science and Business Media LLC. - 1436-6207 .- 1436-6215. ; 55:4, s. 1359-1375
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Tidskriftsartikel (refereegranskat)abstract
- Background/Objectives Polyphenols are plant secondary metabolites with a large variability in their chemical structure and dietary occurrence that have been associated with some protective effects against several chronic diseases. To date, limited data exist on intake of polyphenols in populations. The current cross-sectional analysis aimed at estimating dietary intakes of all currently known individual polyphenols and total intake per class and subclass, and to identify their main food sources in the European Prospective Investigation into Cancer and Nutrition cohort. Methods Dietary data at baseline were collected using a standardized 24-h dietary recall software administered to 36,037 adult subjects. Dietary data were linked with Phenol- Explorer, a database with data on 502 individual polyphenols in 452 foods and data on polyphenol losses due to cooking and food processing. Results Mean total polyphenol intake was the highest in Aarhus—Denmark (1786 mg/day in men and 1626 mg/day in women) and the lowest in Greece (744 mg/day in men and 584 mg/day in women). When dividing the subjects into three regions, the highest intake of total polyphenols was observed in the UK healthconscious group, followed by non-Mediterranean (non- MED) and MED countries. The main polyphenol contributors were phenolic acids (52.5–56.9 %), except in men from MED countries and in the UK health-conscious group where they were flavonoids (49.1–61.7 %). Coffee, tea, and fruits were the most important food sources of total polyphenols. A total of 437 different individual polyphenols were consumed, including 94 consumed at a level [1 mg/day. The most abundant ones were the caffeoylquinic acids and the proanthocyanidin oligomers and polymers. Conclusion This study describes the large number of dietary individual polyphenols consumed and the high variability of their intakes between European populations, particularly between MED and non-MED countries.
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