345 research outputs found
Modeling Hadronic Gamma-ray Emissions from Solar Flares and Prospects for Detecting Non-thermal Signatures from Protostars
We investigate gamma-ray emission in the impulsive phase of solar flares and
the detectability of non-thermal signatures from protostellar flares. Energetic
solar flares emit high-energy gamma rays of GeV energies, but their production
mechanism and emission site are still unknown. Young stellar objects, including
protostars, also exhibit luminous X-ray flares, but the triggering mechanism of
the flaring activity is still unclear due to the strong obscuration.
Non-thermal signatures in mm/sub-mm and gamma-ray bands are useful to probe
protostellar flares owing to their strong penetration power. We develop a
non-thermal emission model of the impulsive phase of solar flares, where
cosmic-ray protons accelerated at the termination shock produce high-energy
gamma rays via hadronuclear interaction with the evaporation plasma. This model
can reproduce gamma-ray data in the impulsive phase of a solar flare. We apply
our model to protostellar flares and show that Cherenkov Telescope Array will
be able to detect gamma rays of TeV energies if particle acceleration in
protostellar flares is efficient. Non-thermal electrons accelerated together
with protons can emit strong mm and sub-mm signals via synchrotron radiation,
whose power is consistent with the energetic mm/sub-mm transients observed from
young stars. Future gamma-ray and mm/sub-mm observations from protostars,
coordinated with a hard X-ray observation, will unravel the triggering
mechanism of non-thermal particle production in protostellar flares.Comment: 19 pages, 5 figures, 1 tabl
Interaction of a Relativistic Magnetized Collisionless Shock with a Dense Clump
The interactions between a relativistic magnetized collisionless shock and
dense clumps have been expected to play a crucial role on the magnetic field
amplification and cosmic-ray acceleration. We investigate this process by
two-dimensional Particle-In-Cell (PIC) simulations for the first time, where
the clump size is much larger than the gyroradius of downstream particles. We
also perform relativistic magnetohydrodynamic (MHD) simulations for the same
condition to see the kinetic effects. We find that particles escape from the
shocked clump along magnetic field lines in the PIC simulations, so that the
vorticity is lower than that in the MHD simulations. Moreover, in both the PIC
and MHD simulations, the shocked clump quickly decelerates because of the
Lorentz contraction. Owing to the escape and the deceleration, the shocked
clump cannot amplify the downstream magnetic field in relativistic
collisionless shocks. This large-scale PIC simulation opens a new window to
understand large-scale behaviors in collisionless plasma systems
BMCs and periodontal tissue healing
Bone marrow-derived cells (BMCs) are considered to be a major source of mesenchymal stem cells (MSCs) in adults and are known to be effective in periodontal tissue regeneration. However, whether endogenous BMCs are involved in periodontal tissue repair process is uncertain. We therefore created periodontal tissue defects in the buccal alveolar bone of mandibular first molars in bone marrow chimeric mice, and immunohistochemically examined the expression of stromal cell derived factor-1 (SDF-1) and the mobilization of BMCs. We found that SDF-1 expression was increased around the defects at as early as 1 week after injury and that BMCs were mobilized to the defects, while GFP+/CD45+ were rarely observed. Fluorescence-activated cell sorting (FACS) analysis demonstrated that the number of platelet-derived growth factor receptor (pdgfr) α+/Sca-1+ (PαS) cells in the bone marrow decreased after injury. Taken together, these results suggest that BMCs are mobilized to the periodontal tissue defects. Recruitment of BMCs, including a subset of MSCs could be a new target of periodontal treatment
High-mass star formation in Orion triggered by cloud-cloud collision II, Two merging molecular clouds in NGC2024
We analyzed the NANTEN2 13CO (J=2-1 and 1-0) datasets in NGC 2024. We found
that the cloud consists of two velocity components, whereas the cloud shows
mostly single-peaked CO profiles. The two components are physically connected
to the HII region as evidenced by their close correlation with the dark lanes
and the emission nebulosity. The two components show complementary distribution
with a displacement of 0.4 pc. Such complementary distribution is typical to
colliding clouds discovered in regions of high-mass star formation. We
hypothesize that cloud-cloud collision between the two components triggered the
formation of the late O stars and early B stars localized within 0.3 pc of the
cloud peak. The collision timescale is estimated to be ~ 10^5 yrs from a ratio
of the displacement and the relative velocity 3-4 km s-1 corrected for probable
projection. The high column density of the colliding cloud 1023 cm-2 is similar
to those in the other massive star clusters in RCW 38, Westerlund 2, NGC 3603,
and M42, which are likely formed under trigger by cloud-cloud collision. The
present results provide an additional piece of evidence favorable to high-mass
star formation by a major cloud-cloud collision in Orion.Comment: 24 pages, 10 figures, submitted for publication in PASJ (cloud-cloud
collision special issue
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