156 research outputs found
Probing the Cosmic X-ray and MeV Gamma-ray Background Radiation through the Anisotropy
While the cosmic soft X-ray background is very likely to originate from
individual Seyfert galaxies, the origin of the cosmic hard X-ray and MeV
gamma-ray background is not fully understood. It is expected that Seyferts
including Compton thick population may explain the cosmic hard X-ray
background. At MeV energy range, Seyferts having non-thermal electrons in
coronae above accretion disks or MeV blazars may explain the background
radiation. We propose that future measurements of the angular power spectra of
anisotropy of the cosmic X-ray and MeV gamma-ray backgrounds will be key to
deciphering these backgrounds and the evolution of active galactic nuclei
(AGNs). As AGNs trace the cosmic large-scale structure, spatial clustering of
AGNs exists. We show that e-ROSITA will clearly detect the correlation signal
of unresolved Seyferts at 0.5-2 keV and 2-10 keV bands and will be able to
measure the bias parameter of AGNs at both bands. Once the future hard X-ray
all sky satellites achieve the sensitivity better than 10^{-12} erg/cm^2/s at
10-30 keV or 30-50 keV - although this is beyond the sensitivities of current
hard X-ray all sky monitors - angular power spectra will allow us to
independently investigate the fraction of Compton-thick AGNs in all Seyferts.
We also find that the expected angular power spectra of Seyferts and blazars in
the MeV range are different by about an order of magnitude, where the Poisson
term, so-called shot noise, is dominant. Current and future MeV instruments
will clearly disentangle the origin of the MeV gamma-ray background through the
angular power spectrum.Comment: 14 pages, 8 figures, accepted for publication in Ap
Probing the birth of fast rotating magnetars through high-energy neutrinos
We investigate the high-energy neutrino emission expected from newly born
magnetars surrounded by their stellar ejecta. Protons might be accelerated up
to 0.1-100 EeV energies possibly by, e.g., the wave dissipation in the winds,
leading to hadronic interactions in the stellar ejecta. The resulting PeV-EeV
neutrinos can be detected by IceCube/KM3Net with a typical peak time scale of a
few days after the birth of magnetars, making the characteristic soft-hard-soft
behavior. Detections would be important as a clue to the formation mechanism of
magnetars, although there are ambiguities coming from uncertainties of several
parameters such as velocity of the ejecta. Non-detections would also lead to
useful constraints on the scenario.Comment: 5 pages, 3 figures, accepted for publication in PR
High-energy cosmic neutrinos as a probe of the vector mediator scenario in light of the muon anomaly and Hubble tension
In light of the recent Muon experiment data from Fermilab, we
investigate the implications of a gauged model for high
energy neutrino telescopes. It has been suggested that a new gauge boson at the
MeV scale can both account for the Muon data and alleviate the tension in
the Hubble parameter measurements. It also strikes signals at IceCube from the
predicted resonance scattering between high-energy neutrinos and the cosmic
neutrino background. We revisit this model based on the latest IceCube shower
data, and perform a four-parameter fit to find a preferred region. While the
data are consistent with the absence of resonant signatures from secret
interactions, we find the preferred region consistent with the muon
anomaly and Hubble tension. We demonstrate that future neutrino telescopes such
as IceCube-Gen2 can probe this unique parameter space, and point out that
successful measurements would infer the neutrino mass with .Comment: 5 pages, 4 figure
High energy neutrino early afterglows from gamma-ray bursts revisited
The high energy neutrino emission from gamma-ray bursts (GRBs) has been
expected in various scenarios. In this paper, we study the neutrino emission
from early afterglows of GRBs, especially under the reverse-forward shock model
and late prompt emission model. In the former model, the early afterglow
emission occurs due to dissipation made by an external shock with the
circumburst medium (CBM). In the latter model, internal dissipation such as
internal shocks produces the shallow decay emission in early afterglows. We
also discuss implications of recent Swift observations for neutrino signals in
detail. Future neutrino detectors such as IceCube may detect neutrino signals
from early afterglows, especially under the late prompt emission model, while
the detection would be difficult under the reverse-forward shock model.
Contribution to the neutrino background from the early afterglow emission may
be at most comparable to that from the prompt emission unless the outflow
making the early afterglow emission loads more nonthermal protons, and it may
be important in the very high energies. Neutrino-detections are inviting
because they could provide us with not only information on baryon acceleration
but also one of the clues to the model of early afterglows. Finally, we compare
various predictions for the neutrino background from GRBs, which are testable
by future neutrino-observations.Comment: 18 pages, 12 figures, accepted for publication in PR
ORP2 couples LDL-cholesterol transport to FAK activation by endosomal cholesterol/PI(4,5)P-2 exchange
Low-density lipoprotein (LDL)-cholesterol delivery from late endosomes to the plasma membrane regulates focal adhesion dynamics and cell migration, but the mechanisms controlling it are poorly characterized. Here, we employed auxin-inducible rapid degradation of oxysterol-binding protein-related protein 2 (ORP2/OSBPL2) to show that endogenous ORP2 mediates the transfer of LDL-derived cholesterol from late endosomes to focal adhesion kinase (FAK)-/integrin-positive recycling endosomes in human cells. In vitro, cholesterol enhances membrane association of FAK to PI(4,5)P-2-containing lipid bilayers. In cells, ORP2 stimulates FAK activation and PI(4,5)P-2 generation in endomembranes, enhancing cell adhesion. Moreover, ORP2 increases PI(4,5)P-2 in NPC1-containing late endosomes in a FAK-dependent manner, controlling their tubulovesicular trafficking. Together, these results provide evidence that ORP2 controls FAK activation and LDL-cholesterol plasma membrane delivery by promoting bidirectional cholesterol/PI(4,5)P-2 exchange between late and recycling endosomes.Peer reviewe
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