| 11. |
- Aharonian, Felix, et al.
(author)
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Temperature structure in the Perseus cluster core observed with Hitomi
- 2018
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In: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 70:2
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Journal article (peer-reviewed)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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| 12. |
- De La Fuente, Eduardo, et al.
(author)
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Detection of a new molecular cloud in the LHAASO J2108+5157 region supporting a hadronic PeVatron scenario
- 2023
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In: Publication of the Astronomical Society of Japan. - 2053-051X .- 0004-6264. ; 75:3, s. 546-566
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Journal article (peer-reviewed)abstract
- PeVatrons are the most powerful naturally occurring particle accelerators in the Universe. The identification of counterparts associated to astrophysical objects such as dying massive stars, molecular gas, star-forming regions, and star clusters is essential to clarify the underlying nature of the PeV emission, i.e., hadronic or leptonic. We present 12,13CO (J = 2→1) observations made with the 1.85 m radio-Telescope of the Osaka Prefecture University toward the Cygnus OB7 molecular cloud, which contains the PeVatron candidate LHAASO J2108+5157. We investigate the nature of the sub-PeV (gamma-ray) emission by studying the nucleon density determined from the content of H i and H2, derived from the CO observations. In addition to MML[2017]4607, detected via the observations of the optically thick 12CO (J = 1→0) emission, we infer the presence of an optically thin molecular cloud, named [FKT-MC]2022, whose angular size is 1-1 ± 0.}^\circ}}2. We propose this cloud as a new candidate to produce the sub-PeV emission observed in LHAASO J2108+5157. Considering a distance of 1.7 kpc, we estimate a nucleon (H i + H2) density of 37 ± 14 cm-3, and a total nucleon mass(H i + H2) of 1.5 ± 0.6 × 104 M·. On the other hand, we confirm that Kronberger 82 is a molecular clump with an angular size of 0°1, a nucleon density ∼103 cm-3, and a mass ∼103 M·. Although Kronberger 82 hosts the physical conditions to produce the observed emission of LHAASO J2108+5157, [FKT-MC]2022 is located closer to it, suggesting that the latter could be the one associated to the sub-PeV emission. Under this scenario, our results favour a hadronic origin for the emission.
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| 13. |
- de la Fuente, Eduardo, et al.
(author)
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The symbiotic and bipolar nebula M2-9: Morphological variability of the collimated ionized wind arising from the core
- 2022
-
In: Publication of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 2053-051X .- 0004-6264. ; 74:3, s. 594-601
-
Journal article (peer-reviewed)abstract
- We studied the central region of bipolar nebula M 2-9 using radio-continuum observations obtained from the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter Array (ALMA) interferometers. This work presents new images at similar to 43 GHz (similar to 7.0 mm) and similar to 345 GHz (similar to 0.9 mm) with angular resolutions of similar to 0 ''.047 and 0 ''.09, respectively. The continuum emission at similar to 43 GHz shows an elongated jet-like structure perpendicular to the similar to 345 GHz observation. We conclude that both emissions could correspond to tracing an isothermal collimated fast wind with constant expansion velocity and being driven by the circumstellar ring traced by ALMA. Although this configuration has been discussed within the scope of planetary nebulae models, there is a remarkable fact: the collimated fast wind shows morphological spatial variability. This supports the idea of a symbiotic binary system within the innermost part of M 2-9, which would be composed of a white dwarf and an AGB star. The latter could explain the mirror symmetry observed at larger scales due to their orbital motion.
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| 14. |
- Dogiel, Vladimir A., et al.
(author)
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Origin of Thermal and Non-Thermal Hard X-Ray Emissionfrom the Galactic Center
- 2009
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In: Publications of the Astronomical Society of Japan. - : Oxford University Press. - 0004-6264 .- 2053-051X. ; 61:5, s. 1099-1105
-
Journal article (peer-reviewed)abstract
- We analyse new results of Chandra and Suzaku Observatories which found a flux of hard X-ray emission from the compact region around Sgr A∗ (r ∼ 100 pc). We suppose that this emission is generated by accretion processes onto the central supermassive blackhole when an unbound part of captured stars obtains an additional momentum. As a result a flux of subrelativistic protons is generated near the galactic center which heats the background plasma up to temperatures about 6–10 keV and produces by inverse bremsstrahlung a flux of non-thermal X-ray emission in the energy range above 10 keV.
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| 15. |
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| 16. |
- Fukui, Akihiko, et al.
(author)
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TOI-2285b: A 1.7 Earth-radius planet near the habitable zone around a nearby M dwarf
- 2022
-
In: Publication of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 2053-051X .- 0004-6264. ; 74:1, s. L1-L8
-
Journal article (peer-reviewed)abstract
- We report the discovery of TO1-2285b, a sub-Neptune-sized planet transiting a nearby (42 pc) M dwarf with a period of 27.3 d. We identified the transit signal from the Transiting Exoplanet Survey Satellite photometric data, which we confirmed with ground-based photometric observations using the multiband imagers MuSCAT2 and MuSCAT3. Combining these data with other follow-up observations including high-resolution spectroscopy with the Tillinghast Reflector Echelle Spectrograph, high-resolution imaging with the SPeckle Polarimeter, and radial velocity (RV) measurements with the InfraRed Doppler instrument, we find that the planet has a radius of 1.74 +/- 0.08 R-circle plus, a mass of <19.5 M-circle plus + (95% c.I.), and an insolation flux of 1.54 +/- 0.14 times that of the Earth. Although the planet resides just outside the habitable zone for a rocky planet, if the planet harbors an H2O layer under a hydrogen-rich atmosphere, then liquid water could exist on the surface of the H2O layer depending on the planetary mass and water mass fraction. The bright host star in the near-infrared (K-s = 9.0) makes this planet an excellent target for further RV and atmospheric observations to improve our understanding of the composition, formation, and habitability of sub-Neptune-sized planets.
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| 17. |
- Harakawa, Hiroki, et al.
(author)
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A super-Earth orbiting near the inner edge of the habitable zone around the M4.5 dwarf Ross 508
- 2022
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In: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 74:4, s. 904-922
-
Journal article (peer-reviewed)abstract
- We report the near-infrared radial velocity (RV) discovery of a super-Earth planet on a 10.77 d orbit around the M4.5 dwarf Ross 508 (Jmag = 9.1). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of 3.92ms−1, corresponding to a planet with a minimum mass msini=4.00M⊕. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semi-major axis of 0.05366au. This gives an orbit-averaged insolation of ≈1.4 times the Earth’s value, placing Ross 508 b near the inner edge of its star’s habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role in finding a low-mass planet around cool M dwarfs like Ross 508.
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| 18. |
- Hashimoto, Takuya, et al.
(author)
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Big Three Dragons: A z=7.15 Lyman-break galaxy detected in [Oiii] 88 mu m, [Cii] 158 mu m, and dust continuum with ALMA
- 2019
-
In: Publication of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 2053-051X .- 0004-6264. ; 71:4
-
Journal article (peer-reviewed)abstract
- We present new ALMA observations and physical properties of a Lyman break galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, M-UV approximate to -22.4, and has been spectroscopically identified in Ly alpha with a small rest-frame equivalent width of approximate to 4 angstrom. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [Oiii] 88 mu m, [Cii] 158 mu m, and their underlying dust continuum emission. In the whole system of B14-65666, the [Oiii] and [Cii] lines have consistent redshifts of 7.1520 +/- 0.0003, and the [Oiii] luminosity, (34.4 +/- 4.1)x 10(8)L(circle dot), is about three times higher than the [Cii] luminosity, (11.0 +/- 1.4) x 10(8)L(circle dot). With our two continuum flux densities, the dust temperature is constrained to be T-d approximate to 50-60K under the assumption of a dust emissivity index of beta(d) = 2.0-1.5, leading to a large total infrared luminosity of L-TIR approximate to 1 x 10(12)L(circle dot). Owing to our high spatial resolution data, we show that the [Oiii] and [Cii] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by approximate to 200kms(-1). We also find these two clumps have comparable UV, infrared, [Oiii], and [Cii] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major merger. The merger interpretation is also supported by the large specific star formation rate (defined as the star formation rate per unit stellar mass), sSFR Gyr(-1), inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [Oiii]-to-[Cii] luminosity ratio.
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| 19. |
- Hayakawa, Ryota, et al.
(author)
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X-ray hot spots in the eastern ear of the supernova remnant W 50 and the microquasar SS 433 system
- 2022
-
In: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 74:3, s. 510-520
-
Journal article (peer-reviewed)abstract
- We examined the X-ray and radio spatial structure at the eastern ear of the W 50/SS 433 system to clarify a characteristic feature of the termination region of the SS 433 jet, and found that a hot spot ahead of the filament structure, which is considered to be a terminal shock of the SS 433 eastern jet, is clearly different from a single point source. The detailed spatial structure of the X-ray emission is finely resolved by Chandra observations, showing that there are two sources. By comparing the point-spread function of Chandra with the radial profiles of the two sources, the northern one is clearly more extended than a point source while the other seems marginally extended. Since there are no point sources nearby, the northern hot spot is likely a localized diffuse source. The northern hot spot spatially corresponds to the peak of the radio emission. Its spatial correlation is confirmed by an X-ray image using XMM-Newton. The X-ray spectra of the two sources are reproduced by a single absorbed power-law but the column density of the northern part is larger by a factor of ∼3. When a radiation model comprising synchrotron emission and inverse Compton emission is applied to the spectral energy distribution of the northern hot spot, the emission from this spot can be explained by the radiation from an electron population accelerated up to 30 TeV in a magnetic field strength of B ≲ 50 μG. This model also agrees with the radio and X-ray data, as well as the upper limit of gamma-ray emission obtained by the Fermi satellite.
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| 20. |
- Horak, Jiri, et al.
(author)
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Alpha-Viscosity Effects in Slender Tori
- 2012
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In: Publications of the Astronomical Society of Japan. - : Oxford University Press (OUP). - 0004-6264 .- 2053-051X. ; 64:4
-
Journal article (peer-reviewed)
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