| 1. |
- Algaba, Juan-Carlos, et al.
(author)
-
Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
- 2021
-
In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 911:1
-
Research review (peer-reviewed)abstract
- In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87's spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
|
|
| 2. |
- Michikami, Tatsuhiro, et al.
(author)
-
Three-axial shape distributions of pebbles, cobbles and boulders smaller than a few meters on asteroid Ryugu
- 2022
-
In: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 381
-
Journal article (peer-reviewed)abstract
- Over a broad size range, the shapes of impact fragments from catastrophic disruptions are distributed around the mean axial ratio 2: √2: 1, irrespective of experimental conditions and target materials. Although most blocks on asteroids are likely to be impact fragments, there is not enough quantitative data for reliable statistics on their three-axial lengths and/or ratios because it is difficult to precisely estimate the heights of the blocks. In this study, we evaluate the heights of blocks on asteroid Ryugu by measuring their shadows. The three-axial ratios of ~4100 small blocks with diameters from 5.0 cm to 7.6 m in Ryugu's equatorial region are investigated using eight close-up images of narrower localities taken at altitudes below 500 m, i.e. at <5.4 cm/pixel resolution, obtained immediately before the second touch-down of the Hayabusa2 spacecraft. The purpose of this study is to investigate the block shape distribution, which is important for understanding the geological history of asteroid Ryugu. Specifically, the shape distribution is compared to laboratory impact fragments. Our observations indicate that the shape distributions of blocks smaller than 1 m on Ryugu are consistent with laboratory impact fragment shape distributions, implying that the dominant shape-determining process for blocks on Ryugu was impact fragmentation. Blocks several meters in size in the equatorial region seem to be slightly flatter than the rest, suggesting that some blocks are partly buried in a bed of regolith. In conclusion, the shape distributions of blocks from several-cm to several-m in the equatorial region of asteroid Ryugu suggest that these are mainly fragments originating from the catastrophic disruption of their parent body and/or from a later impact.
|
|
| 3. |
- Nishizaki, Kazunori, et al.
(author)
-
Programmed cell death in the development of the mouse external auditory canal
- 1998
-
In: Anatomical Record. - 0003-276X .- 1097-0185. ; 252:3, s. 378-82
-
Journal article (peer-reviewed)abstract
- Programmed cell death (PCD) is an essential event for development. The purpose of this work was to ascertain how PCD, in vivo designated apoptosis, is involved in the development of the external auditory canal. We performed a time sequence study of the distribution of apoptosis during the development of external auditory canal (EAC) of the mouse. ICR mice ranging in age from embryonic day 11.5 (E11.5) to 12 days after birth (DAB) were used in the present study. A part of each head including both ears was removed and was processed according to its purpose. Light and electron microscopy for morphological studies and TUNEL method (Gavrieli et al. [1992] J Cell Biol., 119:493-501) for histochemical studies were used. On E11.5, distinct TUNEL-positive staining occurred in the branchial arch. Between E15.5 and 1DAB, TUNEL-positive cells were observed throughout the EAC and the number of these cells decreased with age. On E15.5 and E16.5, numerous TUNEL-positive cells were observed in a cavity remained in the epithelial plate. Transmission electron microscopy revealed that these cells had the features of apoptosis. From 3-12 DAB, no apoptosis was observed in the EAC except for the terminal differentiation of the skin of the EAC. Apoptosis was not observed during recanalization of the EAC, but occurred during the formation of the epithelial plate. The investigation established that PCD is involved in the formation of the epithelial plate, whereas only cornification of the epithelium of the EAC is associated with recanalization.
|
|
| 4. |
- Zeichner, Sarah S., et al.
(author)
-
Polycyclic aromatic hydrocarbons in samples of Ryugu formed in the interstellar medium
- 2023
-
In: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 382:6677, s. 1411-1415
-
Journal article (peer-reviewed)abstract
- Polycyclic aromatic hydrocarbons (PAHs) contain less than or similar to 20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments (at temperatures greater than or similar to 1000 kelvin), by (similar to 10 kelvin) interstellar clouds, or by processing of carbon-rich dust grains. We report isotopic properties of PAHs extracted from samples of the asteroid Ryugu and the meteorite Murchison. The doubly-C-13 substituted compositions (Delta 2x(13)C values) of the PAHs naphthalene, fluoranthene, and pyrene are 9 to 51 parts per thousand higher than values expected for a stochastic distribution of isotopes. The Delta 2x(13)C values are higher than expected if the PAHs formed in a circumstellar environment, but consistent with formation in the interstellar medium. By contrast, the PAHs phenanthrene and anthracene in Ryugu samples have Delta 2x(13)C values consistent with formation by higher-temperature reactions.
|
|
