2,186 research outputs found
Ultrahigh-Energy Photons as a Probe of Nearby Transient Ultrahigh-Energy Cosmic-Ray Sources and Possible Lorentz-Invariance Violation
Detecting neutrinos and photons is crucial to identifying the sources of
ultrahigh-energy cosmic rays (UHECRs), especially for transient sources. We
focus on ultrahigh-energy gamma-ray emission from transient sources such as
gamma-ray bursts, since >EeV gamma rays can be more direct evidence of UHECRs
than PeV neutrinos and GeV-TeV gamma rays. We demonstrate that coincident
detections of about 1-100 events can be expected by current and future UHECR
detectors such as Auger and JEM-EUSO, and the detection probability can be
higher than that of neutrinos for nearby transient sources at <50-100 Mpc. They
may be useful for constraining the uncertain cosmic radio background as well as
knowing the source properties and maximum energy of UHECRs. They can also give
us more than 10^4 times stronger limits on the Lorentz-invariance violation
than current constraints.Comment: 4 pages, 3 figures, replaced to match the published version (PRL,
103, 081102
Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts
We present recipes to diagnose the fireball of gamma-ray bursts (GRBs) by
combining observations of electron-positron pair-signatures (the
pair-annihilation line and the cutoff energy due to the pair-creation process).
Our recipes are largely model-independent and extract information even from the
non-detection of either pair-signature. We evaluate physical quantities such as
the Lorentz factor, optical depth and pair-to-baryon ratio, only from the
observable quantities. In particular, we can test whether the prompt emission
of GRBs comes from the pair/baryonic photosphere or not. The future-coming
Gamma-Ray Large Area Space Telescope (GLAST) satellite will provide us with
good chances to use our recipes by detecting or non-detecting pair-signatures.Comment: 7 pages, 4 figures, accepted for publication in ApJ, with extended
discussions. Conclusions unchange
Neonatal bone fragments for the induction of xenograft acceptance: Transplantation of xenogeneic hematopoietic stem cells and species-specific microenvironment for hematopoiesis
Donor bone marrow cell infusion without recipient cytoablation induces acceptance of rat islet allografts
Complement activation correlates with graft damage in baboon-to-human liver xenotransplantation
Unstable GRB photospheres and electron-positron annihilation lines
We propose an emission mechanism of prompt gamma-ray bursts (GRBs) that can
reproduce the observed non-thermal spectra with high radiative efficiencies,
>50%. Internal dissipation below a photosphere can create a radiation-dominated
thermal fireball. If electron-positron pairs outnumber protons, radiative
acceleration of pairs drives the two-stream instabilities between pairs and
protons, leading to the ``proton sedimentation'' in the accelerating pair
frame. Pairs are continuously shock heated by proton clumps, scattering the
thermal photons into the broken power-law shape, with the non-thermal energy
that is comparable to the proton kinetic energy, consistent with observations.
Pair photospheres become unstable around the radius of the progenitor star
where strong thermalization occurs, if parameters satisfy the observed spectral
(Yonetoku) relation. Pair annihilation lines are predicted above continua,
which could be verified by GLAST.Comment: 4 pages, 2 figure
Weighted Radon transforms for which the Chang approximate inversion formula is precise
We describe all weighted Radon transforms on the plane for which the Chang
approximate inversion formula is precise. Some subsequent results, including
the Cormack type inversion for these transforms, are also given
Pressure Raman effects and internal stress in network glasses
Raman scattering from binary GexSe1-x glasses under hydrostatic pressure
shows onset of a steady increase in the frequency of modes of corner-sharing
GeSe4 tetrahedral units when the external pressure P exceeds a threshold value
Pc. The threshold pressure Pc(x) decreases with x in the 0.15 < x < 0.20 range,
nearly vanishes in the 0.20 < x < 0.25 range, and then increases in the 0.25 <
x < 1/3 range. These Pc(x) trends closely track those in the non-reversing
enthalpy, DHnr(x), near glass transitions (Tgs), and in particular, both
DHnr(x) and Pc(x) vanish in the reversibility window (0.20 < x < 0.25). It is
suggested that Pc provides a measure of stress at the Raman active units; and
its vanishing in the reversibility window suggests that these units are part of
an isostatically rigid backbone. Isostaticity also accounts for the non-aging
behavior of glasses observed in the reversibility window
- …