| 1. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of similar to 50 mu as, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.
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| 2. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. VII. Polarization of the Ring
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 910:1
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Tidskriftsartikel (refereegranskat)abstract
- In 2017 April, the Event Horizon Telescope (EHT) observed the near-horizon region around the supermassive black hole at the core of the M87 galaxy. These 1.3 mm wavelength observations revealed a compact asymmetric ring-like source morphology. This structure originates from synchrotron emission produced by relativistic plasma located in the immediate vicinity of the black hole. Here we present the corresponding linear-polarimetric EHT images of the center of M87. We find that only a part of the ring is significantly polarized. The resolved fractional linear polarization has a maximum located in the southwest part of the ring, where it rises to the level of similar to 15%. The polarization position angles are arranged in a nearly azimuthal pattern. We perform quantitative measurements of relevant polarimetric properties of the compact emission and find evidence for the temporal evolution of the polarized source structure over one week of EHT observations. The details of the polarimetric data reduction and calibration methodology are provided. We carry out the data analysis using multiple independent imaging and modeling techniques, each of which is validated against a suite of synthetic data sets. The gross polarimetric structure and its apparent evolution with time are insensitive to the method used to reconstruct the image. These polarimetric images carry information about the structure of the magnetic fields responsible for the synchrotron emission. Their physical interpretation is discussed in an accompanying publication.
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| 3. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. VIII. Magnetic Field Structure near The Event Horizon
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 910:1
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Tidskriftsartikel (refereegranskat)abstract
- Event Horizon Telescope (EHT) observations at 230 GHz have now imaged polarized emission around the supermassive black hole in M87 on event-horizon scales. This polarized synchrotron radiation probes the structure of magnetic fields and the plasma properties near the black hole. Here we compare the resolved polarization structure observed by the EHT, along with simultaneous unresolved observations with the Atacama Large Millimeter/submillimeter Array, to expectations from theoretical models. The low fractional linear polarization in the resolved image suggests that the polarization is scrambled on scales smaller than the EHT beam, which we attribute to Faraday rotation internal to the emission region. We estimate the average density n(e) similar to 10(4-7) cm(-3), magnetic field strength B similar to 1-30 G, and electron temperature T-e similar to (1-12) x 10(10) K of the radiating plasma in a simple one-zone emission model. We show that the net azimuthal linear polarization pattern may result from organized, poloidal magnetic fields in the emission region. In a quantitative comparison with a large library of simulated polarimetric images from general relativistic magnetohydrodynamic (GRMHD) simulations, we identify a subset of physical models that can explain critical features of the polarimetric EHT observations while producing a relativistic jet of sufficient power. The consistent GRMHD models are all of magnetically arrested accretion disks, where near-horizon magnetic fields are dynamically important. We use the models to infer a mass accretion rate onto the black hole in M87 of (3-20) x 10(-4) M yr(-1).
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| 4. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a "variability noise budget" in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse (u, v)-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of similar to 50 mu as, consistent with the expected "shadow" of a 4 x 10(6) M (circle dot) black hole in the Galactic center located at a distance of 8 kpc.
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| 5. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching similar to 100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8 +/- 2.3 mu as (68% credible intervals), with the ring thickness constrained to have an FWHM between similar to 30% and 50% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8(-0.7)(+1.4) mu as, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0(-0.6)(+1.1) x 10(6) M-circle dot.
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| 6. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we provide a first physical interpretation for the Event Horizon Telescope's (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT observations from radio to X-ray wavelengths to predictions from a library of models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, and stellar-wind-fed simulations; radiative transfer is performed assuming both thermal and nonthermal electron distribution functions. We test the models against 11 constraints drawn from EHT 230 GHz data and observations at 86 GHz, 2.2 mu m, and in the X-ray. All models fail at least one constraint. Light-curve variability provides a particularly severe constraint, failing nearly all strongly magnetized (magnetically arrested disk (MAD)) models and a large fraction of weakly magnetized models. A number of models fail only the variability constraints. We identify a promising cluster of these models, which are MAD and have inclination i <= 30 degrees. They have accretion rate (5.2-9.5) x 10(-9) M (circle dot) yr(-1), bolometric luminosity (6.8-9.2) x 10(35) erg s(-1), and outflow power (1.3-4.8) x 10(38) erg s(-1). We also find that all models with i >= 70 degrees fail at least two constraints, as do all models with equal ion and electron temperature; exploratory, nonthermal model sets tend to have higher 2.2 mu m flux density; and the population of cold electrons is limited by X-ray constraints due to the risk of bremsstrahlung overproduction. Finally, we discuss physical and numerical limitations of the models, highlighting the possible importance of kinetic effects and duration of the simulations.
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| 7. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. VI. Testing the Black Hole Metric
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- Astrophysical black holes are expected to be described by the Kerr metric. This is the only stationary, vacuum, axisymmetric metric, without electromagnetic charge, that satisfies Einstein's equations and does not have pathologies outside of the event horizon. We present new constraints on potential deviations from the Kerr prediction based on 2017 EHT observations of Sagittarius A* (Sgr A*). We calibrate the relationship between the geometrically defined black hole shadow and the observed size of the ring-like images using a library that includes both Kerr and non-Kerr simulations. We use the exquisite prior constraints on the mass-to-distance ratio for Sgr A* to show that the observed image size is within similar to 10% of the Kerr predictions. We use these bounds to constrain metrics that are parametrically different from Kerr, as well as the charges of several known spacetimes. To consider alternatives to the presence of an event horizon, we explore the possibility that Sgr A* is a compact object with a surface that either absorbs and thermally reemits incident radiation or partially reflects it. Using the observed image size and the broadband spectrum of Sgr A*, we conclude that a thermal surface can be ruled out and a fully reflective one is unlikely. We compare our results to the broader landscape of gravitational tests. Together with the bounds found for stellar-mass black holes and the M87 black hole, our observations provide further support that the external spacetimes of all black holes are described by the Kerr metric, independent of their mass.
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| 8. |
- Broderick, Avery E., et al.
(författare)
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Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse (u, v) coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency.
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| 9. |
- Farah, Joseph, et al.
(författare)
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Selective Dynamical Imaging of Interferometric Data
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- Recent developments in very long baseline interferometry (VLBI) have made it possible for the Event Horizon Telescope (EHT) to resolve the innermost accretion flows of the largest supermassive black holes on the sky. The sparse nature of the EHT's (u, v)-coverage presents a challenge when attempting to resolve highly time-variable sources. We demonstrate that the changing (u, v)-coverage of the EHT can contain regions of time over the course of a single observation that facilitate dynamical imaging. These optimal time regions typically have projected baseline distributions that are approximately angularly isotropic and radially homogeneous. We derive a metric of coverage quality based on baseline isotropy and density that is capable of ranking array configurations by their ability to produce accurate dynamical reconstructions. We compare this metric to existing metrics in the literature and investigate their utility by performing dynamical reconstructions on synthetic data from simulated EHT observations of sources with simple orbital variability. We then use these results to make recommendations for imaging the 2017 EHT Sgr A* data set.
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| 10. |
- Goddi, Ciriaco, et al.
(författare)
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Polarimetric Properties of Event Horizon Telescope Targets from ALMA
- 2021
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 910:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results from a full polarization study carried out with the Atacama Large Millimeter/submillimeter Array (ALMA) during the first Very Long Baseline Interferometry (VLBI) campaign, which was conducted in 2017 April in the lambda 3 mm and lambda 1.3 mm bands, in concert with the Global mm-VLBI Array (GMVA) and the Event Horizon Telescope (EHT), respectively. We determine the polarization and Faraday properties of all VLBI targets, including Sgr A*, M87, and a dozen radio-loud active galactic nuclei (AGNs), in the two bands at several epochs in a time window of 10 days. We detect high linear polarization fractions (2%-15%) and large rotation measures (RM > 10(3.3)-10(5.5) rad m(-2)), confirming the trends of previous AGN studies at millimeter wavelengths. We find that blazars are more strongly polarized than other AGNs in the sample, while exhibiting (on average) order-of-magnitude lower RM values, consistent with the AGN viewing angle unification scheme. For Sgr A* we report a mean RM of (-4.2 0.3) x 10(5) rad m(-2) at 1.3 mm, consistent with measurements over the past decade and, for the first time, an RM of (-2.1 0.1) x 10(5) rad m(-2) at 3 mm, suggesting that about half of the Faraday rotation at 1.3 mm may occur between the 3 mm photosphere and the 1.3 mm source. We also report the first unambiguous measurement of RM toward the M87 nucleus at millimeter wavelengths, which undergoes significant changes in magnitude and sign reversals on a one year timescale, spanning the range from -1.2 to 0.3 x 10(5) rad m(-2) at 3 mm and -4.1 to 1.5 x 10(5) rad m(-2) at 1.3 mm. Given this time variability, we argue that, unlike the case of Sgr A*, the RM in M87 does not provide an accurate estimate of the mass accretion rate onto the black hole. We put forward a two-component model, comprised of a variable compact region and a static extended region, that can simultaneously explain the polarimetric properties observed by both the EHT (on horizon scales) and ALMA (which observes the combined emission from both components). These measurements provide critical constraints for the calibration, analysis, and interpretation of simultaneously obtained VLBI data with the EHT and GMVA.
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| 11. |
- Huang, Dan, et al.
(författare)
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Estrogen Receptor beta (ESR2) Transcriptome and Chromatin Binding in a Mantle Cell Lymphoma Tumor Model Reveal the Tumor-Suppressing Mechanisms of Estrogens
- 2022
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Ingår i: Cancers. - : MDPI. - 2072-6694. ; 14:13, s. 3098-
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Tidskriftsartikel (refereegranskat)abstract
- Mantle cell lymphoma (MCL) is a non-Hodgkin lymphoma with one of the highest male-tofemale incidence ratios. The reason for this is not clear, but epidemiological as well as experimental data have suggested a role for estrogens, particularly acting through estrogen receptor beta (ESR2). To study the ESR2 effects on MCL progression, MCL cells sensitive and resistant to the Bruton tyrosine kinase inhibitor ibrutinib were grafted to mice and treated with the ESR2-selective agonist diarylpropionitrile (DPN). The results showed that the DPN treatment of mice grafted with both ibrutinib-sensitive and -resistant MCL tumors resulted in impaired tumor progression. To identify the signaling pathways involved in the impaired tumor progression following ESR2 agonist treatment, the transcriptome and ESR2 binding to target genes were investigated by genome-wide chromatin immunoprecipitation in Granta-519 MCL tumors. DPN-regulated genes were enriched in several biological processes that included cell-cell adhesion, endothelial-mesenchymal transition, nuclear factor-kappaB signaling, vasculogenesis, lymphocyte proliferation, and apoptosis. In addition, downregulation of individual genes, such as SOX11 and MALAT1, that play a role in MCL progression was also observed. Furthermore, the data suggested an interplay between the lymphoma cells and the tumor microenvironment in response to the ESR2 agonist. In conclusion, the results clarify the mechanisms by which estrogens, via ESR2, impair MCL tumor progression and provide a possible explanation for the sex-dependent difference in incidence. Furthermore, targeting ESR2 with a selective agonist may be an additional option when considering the treatment of both ibrutinib-sensitive and -resistant MCL tumors.
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| 12. |
- Issaoun, Sara, et al.
(författare)
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Resolving the Inner Parsec of the Blazar J1924-2914 with the Event Horizon Telescope
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 934:2
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Tidskriftsartikel (refereegranskat)abstract
- The blazar J1924-2914 is a primary Event Horizon Telescope (EHT) calibrator for the Galactic center's black hole Sagittarius A*. Here we present the first total and linearly polarized intensity images of this source obtained with the unprecedented 20 mu as resolution of the EHT. J1924-2914 is a very compact flat-spectrum radio source with strong optical variability and polarization. In April 2017 the source was observed quasi-simultaneously with the EHT (April 5-11), the Global Millimeter VLBI Array (April 3), and the Very Long Baseline Array (April 28), giving a novel view of the source at four observing frequencies, 230, 86, 8.7, and 2.3 GHz. These observations probe jet properties from the subparsec to 100 pc scales. We combine the multifrequency images of J1924-2914 to study the source morphology. We find that the jet exhibits a characteristic bending, with a gradual clockwise rotation of the jet projected position angle of about 90 degrees between 2.3 and 230 GHz. Linearly polarized intensity images of J1924-2914 with the extremely fine resolution of the EHT provide evidence for ordered toroidal magnetic fields in the blazar compact core.
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| 13. |
- Jorstad, S.G., et al.
(författare)
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The Event Horizon Telescope Image of the Quasar NRAO 530
- 2023
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 943:2
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observations of the quasar NRAO 530 with the Event Horizon Telescope (EHT) on 2017 April 5-7, when NRAO 530 was used as a calibrator for the EHT observations of Sagittarius A*. At z = 0.902, this is the most distant object imaged by the EHT so far. We reconstruct the first images of the source at 230 GHz, at an unprecedented angular resolution of similar to 20 mu as, both in total intensity and in linear polarization (LP). We do not detect source variability, allowing us to represent the whole data set with static images. The images reveal a bright feature located on the southern end of the jet, which we associate with the core. The feature is linearly polarized, with a fractional polarization of similar to 5%-8%, and it has a substructure consisting of two components. Their observed brightness temperature suggests that the energy density of the jet is dominated by the magnetic field. The jet extends over 60 mu as along a position angle similar to -28 degrees. It includes two features with orthogonal directions of polarization (electric vector position angle), parallel and perpendicular to the jet axis, consistent with a helical structure of the magnetic field in the jet. The outermost feature has a particularly high degree of LP, suggestive of a nearly uniform magnetic field. Future EHT observations will probe the variability of the jet structure on microarcsecond scales, while simultaneous multiwavelength monitoring will provide insight into the high-energy emission origin.
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| 14. |
- Narayan, Ramesh, et al.
(författare)
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The Polarized Image of a Synchrotron-emitting Ring of Gas Orbiting a Black Hole
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 912:1
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Tidskriftsartikel (refereegranskat)abstract
- Synchrotron radiation from hot gas near a black hole results in a polarized image. The image polarization is determined by effects including the orientation of the magnetic field in the emitting region, relativistic motion of the gas, strong gravitational lensing by the black hole, and parallel transport in the curved spacetime. We explore these effects using a simple model of an axisymmetric, equatorial accretion disk around a Schwarzschild black hole. By using an approximate expression for the null geodesics derived by Beloborodov and conservation of the Walker-Penrose constant, we provide analytic estimates for the image polarization. We test this model using currently favored general relativistic magnetohydrodynamic simulations of M87*, using ring parameters given by the simulations. For a subset of these with modest Faraday effects, we show that the ring model broadly reproduces the polarimetric image morphology. Our model also predicts the polarization evolution for compact flaring regions, such as those observed from Sgr A* with GRAVITY. With suitably chosen parameters, our simple model can reproduce the EVPA pattern and relative polarized intensity in Event Horizon Telescope images of M87*. Under the physically motivated assumption that the magnetic field trails the fluid velocity, this comparison is consistent with the clockwise rotation inferred from total intensity images.
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| 15. |
- Psaltis, Dimitrios, et al.
(författare)
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Gravitational Test beyond the First Post-Newtonian Order with the Shadow of the M87 Black Hole
- 2020
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 125:14
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Tidskriftsartikel (refereegranskat)abstract
- The 2017 Event Horizon Telescope (EHT) observations of the central source in M87 have led to the first measurement of the size of a black-hole shadow. This observation offers a new and clean gravitational test of the black-hole metric in the strong-field regime. We show analytically that spacetimes that deviate from the Kerr metric but satisfy weak-field tests can lead to large deviations in the predicted black-hole shadows that are inconsistent with even the current EHT measurements. We use numerical calculations of regular, parametric, non-Kerr metrics to identify the common characteristic among these different parametrizations that control the predicted shadow size. We show that the shadow-size measurements place significant constraints on deviation parameters that control the second post-Newtonian and higher orders of each metric and are, therefore, inaccessible to weak-field tests. The new constraints are complementary to those imposed by observations of gravitational waves from stellar-mass sources.
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| 16. |
- Satapathy, Kaushik, et al.
(författare)
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The Variability of the Black Hole Image in M87 at the Dynamical Timescale
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 925:1
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Tidskriftsartikel (refereegranskat)abstract
- The black hole images obtained with the Event Horizon Telescope (EHT) are expected to be variable at the dynamical timescale near their horizons. For the black hole at the center of the M87 galaxy, this timescale (5-61 days) is comparable to the 6 day extent of the 2017 EHT observations. Closure phases along baseline triangles are robust interferometric observables that are sensitive to the expected structural changes of the images but are free of station-based atmospheric and instrumental errors. We explored the day-to-day variability in closure-phase measurements on all six linearly independent nontrivial baseline triangles that can be formed from the 2017 observations. We showed that three triangles exhibit very low day-to-day variability, with a dispersion of similar to 3 degrees-5 degrees. The only triangles that exhibit substantially higher variability (similar to 90 degrees-180 degrees) are the ones with baselines that cross the visibility amplitude minima on the u-v plane, as expected from theoretical modeling. We used two sets of general relativistic magnetohydrodynamic simulations to explore the dependence of the predicted variability on various black hole and accretion-flow parameters. We found that changing the magnetic field configuration, electron temperature model, or black hole spin has a marginal effect on the model consistency with the observed level of variability. On the other hand, the most discriminating image characteristic of models is the fractional width of the bright ring of emission. Models that best reproduce the observed small level of variability are characterized by thin ring-like images with structures dominated by gravitational lensing effects and thus least affected by turbulence in the accreting plasmas.
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| 17. |
- Torne, Pablo, et al.
(författare)
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A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set
- 2023
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 959:1
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Tidskriftsartikel (refereegranskat)abstract
- In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz (lambda = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars-which typically exhibit steep emission spectra-are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (less than or similar to 2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.
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| 18. |
- Wielgus, Maciek, et al.
(författare)
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Millimeter Light Curves of Sagittarius A* Observed during the 2017 Event Horizon Telescope Campaign
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) observed the compact radio source, Sagittarius A* (Sgr A*), in the Galactic Center on 2017 April 5-11 in the 1.3 mm wavelength band. At the same time, interferometric array data from the Atacama Large Millimeter/submillimeter Array and the Submillimeter Array were collected, providing Sgr A* light curves simultaneous with the EHT observations. These data sets, complementing the EHT very long baseline interferometry, are characterized by a cadence and signal-to-noise ratio previously unattainable for Sgr A* at millimeter wavelengths, and they allow for the investigation of source variability on timescales as short as a minute. While most of the light curves correspond to a low variability state of Sgr A*, the April 11 observations follow an X-ray flare and exhibit strongly enhanced variability. All of the light curves are consistent with a red-noise process, with a power spectral density (PSD) slope measured to be between -2 and -3 on timescales between 1 minute and several hours. Our results indicate a steepening of the PSD slope for timescales shorter than 0.3 hr. The spectral energy distribution is flat at 220 GHz, and there are no time lags between the 213 and 229 GHz frequency bands, suggesting low optical depth for the event horizon scale source. We characterize Sgr A*'s variability, highlighting the different behavior observed just after the X-ray flare, and use Gaussian process modeling to extract a decorrelation timescale and a PSD slope. We also investigate the systematic calibration uncertainties by analyzing data from independent data reduction pipelines.
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| 19. |
- Wielgus, Maciek, et al.
(författare)
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Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 901:1
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature-a ring with azimuthal brightness asymmetry-and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009-2017 to be consistent with a persistent asymmetric ring of similar to 40 mu as diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.
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| 20. |
- Bai, Yunfei, et al.
(författare)
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Sustainable cellulose foams for all-weather high-performance radiative cooling and building insulation
- 2024
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Ingår i: Carbohydrate Polymers. - 0144-8617 .- 1879-1344. ; 333, s. 121951-
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Tidskriftsartikel (refereegranskat)abstract
- Passive daytime radiative cooling (PDRC) as a zero-energy-consumption cooling technique offers rich opportunities in reducing global energy consumption and mitigating CO2 emissions. Developing high-performance PDRC coolers with practical applicability based on sustainable materials is of great significance, but remains a big challenge. Herein, polyvinyl alcohol (PVA) and esterified cellulose (EC) extracted from sawdust were used as raw materials to construct foams by using a dual-crosslinking assisted-unidirectional freeze-drying strategy followed by hydrophobic surface modification. The resultant PVA/EC (PEC) foams with ideal hierarchical macropore structure displayed various excellent features, such as low thermal conductivity (26.2 mW·m−1·K−1), high solar reflectance (95 %) and infrared emissivity (0.97), superhydrophobicity as well as high mechanical properties. The features allowed the PEC foams to be used as radiative coolers with excellent PDRC performance and thermal insulating materials. A maximum sub-ambient temperature drops of 10.2 °C could be achieved for optimal PEC foams. Building simulations indicated that PEC foams could save 55.8 % of the energy consumption for Xi'an. Our work would give inspiration for designing various types of PDRC coolers, including but certainly not limited to foams-based radiative coolers.
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| 21. |
- Cao, Yuehan, et al.
(författare)
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Modulating electron density of vacancy site by single Au atom for effective CO2 photoreduction
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- The surface electron density significantly affects the photocatalytic efficiency, especially the photocatalytic CO2 reduction reaction, which involves multi-electron participation in the conversion process. Herein, we propose a conceptually different mechanism for surface electron density modulation based on the model of Au anchored CdS. We firstly manipulate the direction of electron transfer by regulating the vacancy types of CdS. When electrons accumulate on vacancies instead of single Au atoms, the adsorption types of CO2 change from physical adsorption to chemical adsorption. More importantly, the surface electron density is manipulated by controlling the size of Au nanostructures. When Au nanoclusters downsize to single Au atoms, the strong hybridization of Au 5d and S 2p orbits accelerates the photo-electrons transfer onto the surface, resulting in more electrons available for CO2 reduction. As a result, the product generation rate of AuSA/Cd1−xS manifests a remarkable at least 113-fold enhancement compared with pristine Cd1−xS.
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| 22. |
- Fu, Jie, et al.
(författare)
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Nanoporous CoP nanowire arrays decorated with carbon-coated CoP nanoparticles: the role of interfacial engineering for efficient overall water splitting
- 2022
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Ingår i: International Journal of Energy Research. - : WILEY. - 0363-907X .- 1099-114X. ; 46:8, s. 11359-11370
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Tidskriftsartikel (refereegranskat)abstract
- The innovative construction of bifunctional non-noble electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for electrochemical water splitting. Herein, we provide a collaborative self-templating method to prepare a hybrid catalyst of nanoporous CoP nanowire (NWs) arrays decorated with carbon-coated CoP nanoparticles (NPs). Its found that the unique structure and morphology of the resultant catalyst can provide abundant available active sites and faciliatate the rapid H-2/O-2 transmission. Additionally, the N-doped carbon improves the conductivity of the catalyst and prevents the aggregation and deactivation of CoP nanoparticles. Forthermore, the strong coupling and synergistic effects by interface engineering are also conducive to the electrochemical performance. Benefiting from these advantages, the CoP NWs/CoP NPs@NC/CC only needs a low overpotential of 103 mV to achieve 10 mA cm(-2) with a small Tafel slope of 87 mV dec(-1) for HER. When employed in an electrolytic cell as an electrocatalyst for overall water splitting, a low voltage of 1.60 V is required to drive 10 mA cm(-2). This study may provide a novel way to fabricate transitionmetal-based catalysts for water splitting.
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| 23. |
- Huang, Shoushuang, et al.
(författare)
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Construction of Fe-doped NiS-NiS2 Heterostructured Microspheres Via Etching Prussian Blue Analogues for Efficient Water-Urea Splitting
- 2022
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Ingår i: Small. - : Wiley-V C H Verlag GMBH. - 1613-6810 .- 1613-6829. ; 18:14
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Tidskriftsartikel (refereegranskat)abstract
- Developing efficient and robust non-precious-metal-based catalysts to accelerate electrocatalytic reaction kinetics is crucial for electrochemical water-urea splitting. Herein, Fe-doped NiS-NiS2 heterostructured microspheres, an electrocatalyst, are synthesized via etching Prussian blue analogues following a controlled annealing treatment. The resulting microspheres are constructed by mesoporous nanoplates, granting the virtues of large surface areas, high structural void porosity, and accessible inner surface. These advantages not only provide more redox reaction centers but also strengthen structural robustness and effectively facilitate the mass diffusion and charge transport. Density functional theory simulations validate that the Fe-doping improves the conductivity of nickel sulfides, whereas the NiS-NiS2 heterojunctions induce interface charge rearrangement for optimizing the adsorption free energy of intermediates, resulting in a low overpotential and high electrocatalytic activity. Specifically, an ultralow overpotential of 270 mV at 50 mA cm(-2) for the oxygen evolution reaction (OER) is achieved. After adding 0.33 M urea into 1 M KOH, Fe-doped NiS-NiS2 obtains a strikingly reduced urea oxidation reaction potential of 1.36 V to reach 50 mA cm(-2), around 140 mV less than OER. This work provides insights into the synergistic modulation of electrocatalytic activity of non-noble catalysts for applications in energy conversion systems.
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| 24. |
- Huang, Shoushuang, et al.
(författare)
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Encapsulating Fe2O3 Nanotubes into Carbon-Coated Co9S8 Nanocages Derived from a MOFs-Directed Strategy for Efficient Oxygen Evolution Reactions and Li-Ions Storage
- 2021
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Ingår i: Small. - : Wiley-V C H Verlag GMBH. - 1613-6810 .- 1613-6829. ; 17:51
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Tidskriftsartikel (refereegranskat)abstract
- The development of high-efficiency, robust, and available electrode materials for oxygen evolution reaction (OER) and lithium-ion batteries (LIBs) is critical for clean and sustainable energy system but remains challenging. Herein, a unique yolk-shell structure of Fe2O3 nanotube@hollow Co9S8 nanocage@C is rationally prepared. In a prearranged sequence, the fabrication of Fe2O3 nanotubes is followed by coating of zeolitic imidazolate framework (ZIF-67) layer, chemical etching of ZIF-67 by thioacetamide, and eventual annealing treatment. Benefiting from the hollow structures of Fe2O3 nanotubes and Co9S8 nanocages, the conductivity of carbon coating and the synergy effects between different components, the titled sample possesses abundant accessible active sites, favorable electron transfer rate, and exceptional reaction kinetics in the electrocatalysis. As a result, excellent electrocatalytic activity for alkaline OER is achieved, which delivers a low overpotential of 205 mV at the current density of 10 mA cm(-2) along with the Tafel slope of 55 mV dec(-1). Moreover, this material exhibits excellent high-rate capability and excellent cycle life when employed as anode material of LIBs. This work provides a novel approach for the design and the construction of multifunctional electrode materials for energy conversion and storage.
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| 25. |
- Huang, Shoushuang, et al.
(författare)
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Hierarchical CoFe LDH/MOF nanorods array with strong coupling effect grown on carbon cloth enables efficient oxidation of water and urea
- 2021
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Ingår i: Nanotechnology. - : IOP PUBLISHING LTD. - 0957-4484 .- 1361-6528. ; 32:38
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen evolution reaction (OER) and urea oxidation reaction (UOR) play important roles in the fields of hydrogen energy production and pollution treatment. Herein, a facile one-step chemical etching strategy is provided for fabricating one-dimensional hierarchical nanorods array composed of CoFe layered double hydroxide (LDH)/metal-organic frameworks (MOFs) supported on carbon cloth as efficient and stable OER and UOR catalysts. By precisely controlling the etching rate, the ligands from Co-MOFs are partially removed, the corresponding metal centers then coordinate with hydroxyl ions to generate ultrathin amorphous CoFe LDH nanosheets. The resultant CoFe LDH/MOFs catalyst possesses large active surface area, enhanced conductivity and extended electron/mass transfer channels, which are beneficial for catalytic reactions. Additionally, the intimate contact between CoFe LDH and MOFs modulates the local electronic structure of the catalytic active site, leading to enhanced adsorption of oxygen-containing intermediates to facilitate fast electrocatalytic reaction. As a result, the optimized CoFe LDH/MOF-0.06 exhibits superior OER activity with a low overpotential of 276 at a current density of 10 mA cm(-2) with long-term durability. Additionally, it merely requires a voltage of 1.45 V to obtain 10 mA cm(-2) in 1 M KOH solution with 0.33 urea and is 56 mV lower than the one in pure KOH. The work presented here may hew out a brand-new route to construct multi-functional electrocatalysts for water splitting, CO2 reduction, nitrogen reduction reactions and so on.
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| 26. |
- Huang, Shoushuang, et al.
(författare)
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P-doped Co3S4/NiS2 heterostructures embedded in N-doped carbon nanoboxes: Synergistical electronic structure regulation for overall water splitting
- 2023
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Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 652, s. 369-379
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Tidskriftsartikel (refereegranskat)abstract
- Water splitting using transition metal sulfides as electrocatalysts has gained considerable attention in the field of renewable energy. However, their electrocatalytic activity is often hindered by unfavorable free energies of adsorbed hydrogen and oxygen-containing intermediates. Herein, phosphorus (P)-doped Co3S4/NiS2 hetero-structures embedded in N-doped carbon nanoboxes were rationally synthesized via a pyrolysis-sulfidation-phosphorization strategy. The hollow structure of the carbon matrix and the nanoparticles contained within it not only result in a high specific surface area, but also protects them from corrosion and acts as a conductive pathway for efficient electron transfer. Density functional theory (DFT) calculations indicate that the intro-duction of P dopants improves the conductivity of NiS2 and Co3S4, promotes the charge transfer process, and creates new electrocatalytic sites. Additionally, the NiS2-Co3S4 heterojunctions can enhance the adsorption efficiency of hydrogen intermediates (H*) and lower the energy barrier of water splitting via a synergistic effect with P-doping. These characteristics collectively enable the titled catalyst to exhibit excellent electrocatalytic activity for water splitting in alkaline medium, requiring only small overpotentials of 150 and 257 mV to achieve a current density of 10 mA cm-2 for hydrogen and oxygen evolution reactions, respectively. This work sheds light on the design and optimization of efficient electrocatalysts for water splitting, with potential implications for renewable energy production.
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| 27. |
- Huang, Shoushuang, et al.
(författare)
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Synergistically modulating electronic structure of NiS2 hierarchical architectures by phosphorus doping and sulfur-vacancies defect engineering enables efficient electrocatalytic water splitting
- 2021
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Ingår i: Chemical Engineering Journal. - : ELSEVIER SCIENCE SA. - 1385-8947 .- 1873-3212. ; 420
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Tidskriftsartikel (refereegranskat)abstract
- The synergistic achievement of heteroatom doping, defect engineering and appropriate structural design is efficient to adjust and boost the catalytic performance of catalysts yet challenging. Herein, phosphorus (P)-doped NiS2 hierarchical architectures with sulfur vacancies are synthesized via a Prussian-blue-analogue-sacrificed strategy followed by a phosphidation process. By modulation of P doping and sulfur vacancies, the optimal catalyst manifests outstanding electrocatalytic activities, affording low overpotentials of 73 mV at 10 mA cm-2 for hydrogen evolution reaction (HER), and 255 mV at 20 mA cm-2 for oxygen evolution reaction (OER), respectively. Density functional theory calculations certify that the P dopant not only serves as the new active sites, but also activates the electrochemical activity of neighboring Ni and S sites. Moreover, the synergistic effect of P-doping and sulfur vacancies further improve electrochemical activities of HER and OER by optimizing the adsorption free energy of hydrogen (Delta GH*) and oxygen-containing intermediates (OH*, O* and OOH*), respectively. This finding provides a directive strategy to achieve efficient non-noble metal catalysts for energy conversion and storage.
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| 28. |
- Leng, Jiewu, et al.
(författare)
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Unlocking the power of industrial artificial intelligence towards Industry 5.0: Insights, pathways, and challenges
- 2024
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Ingår i: Journal of manufacturing systems. - : Elsevier BV. - 0278-6125 .- 1878-6642. ; 73, s. 349-363
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Forskningsöversikt (refereegranskat)abstract
- With the continuous development of human-centric, resilient, and sustainable manufacturing towards Industry 5.0, Artificial Intelligence (AI) has gradually unveiled new opportunities for additional functionalities, new features, and tendencies in the industrial landscape. On the other hand, the technology-driven Industry 4.0 paradigm is still in full swing. However, there exist many unreasonable designs, configurations, and implementations of Industrial Artificial Intelligence (IndAI) in practice before achieving either Industry 4.0 or Industry 5.0 vision, and a significant gap between the individualized requirement and actual implementation result still exists. To provide insights for designing appropriate models and algorithms in the upgrading process of the industry, this perspective article classifies IndAI by rating the intelligence levels and presents four principles of implementing IndAI. Three significant opportunities of IndAI, namely, collaborative intelligence, self-learning intelligence, and crowd intelligence, towards Industry 5.0 vision are identified to promote the transition from a technology-driven initiative in Industry 4.0 to the coexistence and interplay of Industry 4.0 and a value-oriented proposition in Industry 5.0. Then, pathways for implementing IndAI towards Industry 5.0 together with key empowering techniques are discussed. Social barriers, technology challenges, and future research directions of IndAI are concluded, respectively. We believe that our effort can lay a foundation for unlocking the power of IndAI in futuristic Industry 5.0 research and engineering practice.
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| 29. |
- Liang, Jiasheng, et al.
(författare)
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Crystalline Structure-Dependent Mechanical and Thermoelectric Performance in Ag2Se1-xSx System
- 2020
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Ingår i: RESEARCH. - : American Association for the Advancement of Science (AAAS). - 2639-5274. ; 2020
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Tidskriftsartikel (refereegranskat)abstract
- Self-powered wearable electronics require thermoelectric materials simultaneously with a high dimensionless figure of merit (zT) and good flexibility to convert the heat discharged by the human body into electricity. Ag-2(S,Se)-based semiconducting materials can well satisfy these requirements, and thus, they are attracting great attention in thermoelectric society recently. Ag-2(S,Se) crystalizes in an orthorhombic structure or monoclinic structure, depending on the detailed S/Se atomic ratio, but the relationship between its crystalline structure and mechanical/thermoelectric performance is still unclear to date. In this study, a series of Ag2Se1-xSx (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.45) samples were prepared and their mechanical and thermoelectric performance dependence on the crystalline structure was systematically investigated. x = 0.3 in the Ag2Se1-xSx system was found to be the transition boundary between orthorhombic and monoclinic structures. Mechanical property measurement shows that the orthorhombic Ag2Se1-xSx samples are brittle while the monoclinic Ag2Se1-xSx samples are ductile and flexible. In addition, the orthorhombic Ag2Se1-xSx samples show better electrical transport performance and higher zT than the monoclinic samples under a comparable carrier concentration, most likely due to their weaker electron-phonon interactions. This study sheds light on the further development of flexible inorganic TE materials.
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| 30. |
- Song, Dandan, et al.
(författare)
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ER alpha and ER beta Homodimers in the Same Cellular Context Regulate Distinct Transcriptomes and Functions
- 2022
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Ingår i: Frontiers in Endocrinology. - : Frontiers Media SA. - 1664-2392. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- The two estrogen receptors ER alpha and ER beta are nuclear receptors that bind estrogen (E2) and function as ligand-inducible transcription factors. They are homologues and can form dimers with each other and bind to the same estrogen-response element motifs in the DNA. ER alpha drives breast cancer growth whereas ER beta has been reported to be anti-proliferative. However, they are rarely expressed in the same cells, and it is not fully investigated to which extent their functions are different because of inherent differences or because of different cellular context. To dissect their similarities and differences, we here generated a novel estrogen-dependent cell model where ER alpha homodimers can be directly compared to ER beta homodimers within the identical cellular context. By using CRISPR-cas9 to delete ER alpha in breast cancer MCF7 cells with Tet-Off-inducible ER beta expression, we generated MCF7 cells that express ER beta but not ER alpha. MCF7 (ER beta only) cells exhibited regulation of estrogen-responsive targets in a ligand-dependent manner. We demonstrated that either ER was required for MCF7 proliferation, but while E2 increased proliferation via ER alpha, it reduced proliferation through a G2/M arrest via ER beta. The two ERs also impacted migration differently. In absence of ligand, ER beta increased migration, but upon E2 treatment, ER beta reduced migration. E2 via ER alpha, on the other hand, had no significant impact on migration. RNA sequencing revealed that E2 regulated a transcriptome of around 800 genes via each receptor, but over half were specific for either ER alpha or ER beta (417 and 503 genes, respectively). Functional gene ontology enrichment analysis reinforced that E2 regulated cell proliferation in opposite directions depending on the ER, and that ER beta specifically impacted extracellular matrix organization. We corroborated that ER beta bound to cis-regulatory chromatin of its unique proposed migration-related direct targets ANXA9 and TFAP2C. In conclusion, we demonstrate that within the same cellular context, the two ERs regulate cell proliferation in the opposite manner, impact migration differently, and each receptor also regulates a distinct set of target genes in response to E2. The developed cell model provides a novel and valuable resource to further complement the mechanistic understanding of the two different ER isoforms.
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| 31. |
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