| 11. |
- Aharonian, Felix, et al.
(författare)
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Solar abundance ratios of the iron-peak elements in the Perseus cluster
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7681, s. 478-
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Tidskriftsartikel (refereegranskat)abstract
- The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).
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| 12. |
- Aharonian, Felix, et al.
(författare)
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Temperature structure in the Perseus cluster core observed with Hitomi
- 2018
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Ingår i: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
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Tidskriftsartikel (refereegranskat)abstract
- The present paper explains the temperature structure of X-ray emitting plasma in the core of the Perseus cluster based on 1.8-20.0 keV data obtained with the Soft X-ray Spectrometer (SXS) on board the Hitomi Observatory. A series of four observations was carried out, with a total effective exposure time of 338 ks that covered a central region of similar to 7' in diameter. SXS was operated with an energy resolution of similar to 5 eV (full width at half maximum) at 5.9 keV. Not only fine structures of K-shell lines in He-like ions, but also transitions from higher principal quantum numbers were clearly resolved from Si through Fe. That enabled us to perform temperature diagnostics using the line ratios of Si, S, Ar, Ca, and Fe, and to provide the first direct measurement of the excitation temperature and ionization temperature in the Perseus cluster. The observed spectrum is roughly reproduced by a single-temperature thermal plasma model in collisional ionization equilibrium, but detailed line-ratio diagnostics reveal slight deviations from this approximation. In particular, the data exhibit an apparent trend of increasing ionization temperature with the atomic mass, as well as small differences between the ionization and excitation temperatures for Fe, the only element for which both temperatures could be measured. The best-fit two-temperature models suggest a combination of 3 and 5 keV gas, which is consistent with the idea that the observed small deviations from a single-temperature approximation are due to the effects of projecting the known radial temperature gradient in the cluster core along the line of sight. A comparison with the Chandra/ACIS and the XMM-Newton/RGS results, on the other hand, suggests that additional lower-temperature components are present in the intracluster medium (ICM), but not detectable with Hitomi/SXS giving its 1.8-20 keV energy band.
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| 13. |
- Balducci, Francesco, et al.
(författare)
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A formaldehyde-free adhesive for particleboards based on soy flour, magnesium oxide, and a plant-derived enzymatic hydrolysate
- 2020
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Ingår i: BioResources. - : North Carolina State University. - 1930-2126 .- 1930-2126. ; 15:2, s. 3087-3102
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Tidskriftsartikel (refereegranskat)abstract
- An adhesive for particleboards based on natural materials was prepared. Soy flour (38.9 wt%), magnesium oxide (MgO) (2.8 wt%), and a hydrolysate from an agricultural crop (13.9 wt%) were mixed with water and ground in a ball mill at 44% solids. The solubility and interaction of the soy flour proteins and the proteins contained in the plant hydrolysate were triggered by the strong basic environment created by MgO in the presence of water. The natural adhesive appeared to be thermally stable at temperatures from 130 °C to 240 °C, with unchanged mass and no major signals in the thermal analysis curves. These results, together with a viscosity of 510 Pa·s at 25 °C, suggested a good operability of the adhesive. Three-layered particleboards were manufactured with weight combinations of natural adhesive and polyamidoamine-epichlorohydrin (PAE) of 0%:100%, 33%:67%, 50%:50%, 67%:33%, and 100%:0%. The natural adhesive showed inferior internal bond strength and poor water resistance compared with urea-formaldehyde-bonded boards. Addition of the PAE significantly improved the internal bond and swelling, and for all the combinations these properties were comparable or, in most cases, better than in the urea-formaldehyde controls. All boards were formaldehyde-free, while the natural adhesive itself released no dangerous volatile substances
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| 14. |
- Reynolds, Christopher S., et al.
(författare)
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Astrophysical Limits on Very Light Axion-like Particles from Chandra Grating Spectroscopy of NGC 1275
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 890:1
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Tidskriftsartikel (refereegranskat)abstract
- Axions/axion-like particles (ALPs) are a well-motivated extension of the Standard Model and are generic within String Theory. The X-ray transparency of the intracluster medium (ICM) in galaxy clusters is a powerful probe of light ALPs (with mass <10(-11)eV); as X-ray photons from an embedded or background source propagate through the magnetized ICM, they may undergo energy-dependent quantum mechanical conversion into ALPs (and vice versa), imprinting distortions on the X-ray spectrum. We present Chandra data for the active galactic nucleus NGC 1275 at the center of the Perseus cluster. Employing a 490 ks High Energy Transmission Gratings exposure, we obtain a high-quality 1-9 keV spectrum free from photon pileup and ICM contamination. Apart from iron-band features, the spectrum is described by a power-law continuum, with any spectral distortions at the <3% level. We compute photon survival probabilities as a function of ALP mass m(a) and ALP-photon coupling constant g(alpha gamma) for an ensemble of ICM magnetic field models, and then use the NGC 1275 spectrum to constrain the (m(a), g(alpha gamma))-plane. Marginalizing over magnetic field realizations, the 99.7% credible region limits the ALP-photon coupling to G(alpha gamma) < 6 - 8 x 10(-13) GeV-1 (depending upon magnetic field model) for masses m(a) < 1 x 10(-12) eV. These are the most stringent limit to date on g(alpha gamma) for these light ALPs, and have already reached the sensitivity limits of next-generation helioscopes and light-shining-through-wall experiments. We highlight the potential of these studies with the next-generation X-ray observatories Athena and Lynx, but note the critical importance of advances in relative calibration of these future X-ray spectrometers.
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| 15. |
- Svoboda, Jiří, et al.
(författare)
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Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State
- 2024
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 966:2
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Tidskriftsartikel (refereegranskat)abstract
- Black hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift J1727.8–1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2–8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer (IXPE) to be ≈4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion disk emission. We find that the polarization degree has dropped dramatically to ≲1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by upscattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system.
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| 16. |
- Wang, Yanan, et al.
(författare)
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Rapid Dimming Followed by a State Transition: A Study of the Highly Variable Nuclear Transient AT 2019avd over 1000+ Days
- 2024
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 962:1
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Tidskriftsartikel (refereegranskat)abstract
- The tidal disruption of a star around a supermassive black hole (SMBH) offers a unique opportunity to study accretion onto an SMBH on a human timescale. We present results from our 1000+ days monitoring campaign of AT 2019avd, a nuclear transient with tidal-disruption-event-like properties, with NICER, Swift, and Chandra. Our primary finding is that approximately 225 days following the peak of the X-ray emission, there is a rapid drop in luminosity exceeding 2 orders of magnitude. This X-ray dropoff is accompanied by X-ray spectral hardening, followed by a plateau phase of 740 days. During this phase, the spectral index decreases from 6.2 ± 1.1 to 2.3 ± 0.4, while the disk temperature remains constant. Additionally, we detect pronounced X-ray variability, with an average fractional rms amplitude of 47%, manifesting over timescales of a few dozen minutes. We propose that this phenomenon may be attributed to intervening clumpy outflows. The overall properties of AT 2019avd suggest that the accretion disk evolves from a super-Eddington to a sub-Eddington luminosity state, possibly associated with a compact jet. This evolution follows a pattern in the hardness-intensity diagram similar to that observed in stellar-mass BHs, supporting the mass invariance of accretion-ejection processes around BHs
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