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| 2. |
- Abdo, A. A., et al.
(författare)
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Gamma-ray emission concurrent with the nova in the symbiotic binary V407 cygni
- 2010
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 329:5993, s. 817-821
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Tidskriftsartikel (refereegranskat)abstract
- Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable γ-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce π0 decay γ-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.
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| 3. |
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| 4. |
- Lavraud, B., et al.
(författare)
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Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:7, s. 3042-3050
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Tidskriftsartikel (refereegranskat)abstract
- Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90 degrees away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials).
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| 5. |
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| 6. |
- Wang, S. Y., et al.
(författare)
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Band structures in I-123
- 2006
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Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 32:3, s. 283-294
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Tidskriftsartikel (refereegranskat)abstract
- Excited states of I-123 were populated via the Cd-116(N-14, alpha 3n) reaction at 65 MeV. The resultant gamma-rays were detected using standard gamma-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity Delta I = 2 sequences have been extended up to 31/2(+) and 41/2(+). In addition, a number of Delta I = 1 transitions linking the two Delta I = 2 sequences have been observed. It is suggested that both Delta I = 2 sequences are based on a common configuration. This Delta I = 1 band is proposed to be built predominantly on the 97/2[404]7/2(+) oblate configuration, based on the energylevel spectra, B(MI)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified Delta I = 1 rotational band built on the prolate g(9/2)[404]9/2(+) orbital has also been extended to higher spins. Another previously identified but weakly populated Delta I = 1 band is confirmed and is proposed to be built on the d(5/2)[413]5/2' configuration with the ground state of I-123 as the bandhead.
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| 7. |
- Wang, S. Y., et al.
(författare)
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High-spin level scheme of Cs-126
- 2004
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Ingår i: Gaoneng wuli yu he wuli. - 0254-3052. ; 28:5, s. 491-494
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Tidskriftsartikel (refereegranskat)abstract
- High-spin states of Cs-126 have been populated via the Cd-116(N-14, 4n) Cs-126 reaction. The experiment was performed at Niels Bohr Institute in Denmark in 1991. After careful data analysis, most of the previously-known bands have been pushed up to much higher spins and 3 new rotational sequences have been identified. Spin, parity and configuration assignments are tentatively proposed for all of the observed bands.
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| 8. |
- Wang, S. Y., et al.
(författare)
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Structure of the pi g(7/2) 404 7/2(+) band in odd proton nucleus I-123
- 2004
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Ingår i: Chinese Physics Letters. - 0256-307X .- 1741-3540. ; 21:6, s. 1024-1026
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Tidskriftsartikel (refereegranskat)abstract
- High spin states of the odd proton nucleus I-123 have been populated in the reaction Cd-116(N-14, 5n2p) at a beam energy of 65 MeV. Two previously known positive-parity DeltaI = 2 sequences have been extended up to 31/2(+) and 41/2(+). In addition, a number of DeltaI = 1 transitions linking the two DeltaI = 2 sequences have been observed. It is suggested that both the DeltaI = 2 sequences are built upon the oblate pi(g) (7/2)[404]7/2(+) Nilsson configuration.
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| 9. |
- Chomiuk, L., et al.
(författare)
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Binary orbits as the driver of gamma-ray emission and mass ejection in classical novae
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 514:7522, s. 339-
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Tidskriftsartikel (refereegranskat)abstract
- Classical novae are the most common astrophysical thermonuclear explosions, occurring on the surfaces of white dwarf stars accreting gas from companions in binary star systems(1). Novae typically expel about 10(-4) solar masses of material at velocities exceeding 1,000 kilometres per second. However, the mechanism of mass ejection in novae is poorly understood, and could be dominated by the impulsive flash of thermonuclear energy(2), prolonged optically thick winds(3) or binary interaction with the nova envelope(4). Classical novae are now routinely detected at gigaelectronvolt gamma-ray wavelengths(5), suggesting that relativistic particles are accelerated by strong shocks in the ejecta. Here we report high-resolution radio imaging of the gamma-ray-emitting nova V959 Mon. We find that its ejecta were shaped by the motion of the binary system: some gas was expelled rapidly along the poles as a wind from the white dwarf, while denser material drifted out along the equatorial plane, propelled by orbital motion(6,7). At the interface between the equatorial and polar regions, we observe synchrotron emission indicative of shocks and relativistic particle acceleration, thereby pinpointing the location of gamma-ray production. Binary shaping of the nova ejecta and associated internal shocks are expected to be widespread among novae(8), explaining why many novae are gamma-ray emitters(5).
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| 10. |
- Aharonian, Felix, et al.
(författare)
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Atomic data and spectral modeling constraints from high-resolution X-ray observations of the Perseus cluster 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 Hitomi Soft X-ray Spectrometer spectrum of the Perseus cluster, with similar to 5 eV resolution in the 2-9 keV band, offers an unprecedented benchmark of the atomic modeling and database for hot collisional plasmas. It reveals both successes and challenges of the current atomic data and models. The latest versions of AtomDB/APEC (3.0.8), SPEX (3.03.00), and CHIANTI (8.0) all provide reasonable fits to the broad-band spectrum, and are in close agreement on best-fit temperature, emission measure, and abundances of a few elements such as Ni. For the Fe abundance, the APEC and SPEX measurements differ by 16%, which is 17 times higher than the statistical uncertainty. This is mostly attributed to the differences in adopted collisional excitation and dielectronic recombination rates of the strongest emission lines. We further investigate and compare the sensitivity of the derived physical parameters to the astrophysical source modeling and instrumental effects. The Hitomi results show that accurate atomic data and models are as important as the astrophysical modeling and instrumental calibration aspects. Substantial updates of atomic databases and targeted laboratory measurements are needed to get the current data and models ready for the data from the next Hitomi-level mission.
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