509 research outputs found
Diffuse PeV neutrinos from gamma-ray bursts
The IceCube collaboration recently reported the potential detection of two
cascade neutrino events in the energy range 1-10 PeV. We study the possibility
that these PeV neutrinos are produced by gamma-ray bursts (GRBs), paying
special attention to the contribution by untriggered GRBs that elude detection
due to their low photon flux. Based on the luminosity function, rate
distribution with redshift and spectral properties of GRBs, we generate, using
Monte-Carlo simulation, a GRB sample that reproduce the observed fluence
distribution of Fermi/GBM GRBs and an accompanying sample of untriggered GRBs
simultaneously. The neutrino flux of every individual GRBs is calculated in the
standard internal shock scenario, so that the accumulative flux of the whole
samples can be obtained. We find that the neutrino flux in PeV energies
produced by untriggered GRBs is about 2 times higher than that produced by the
triggered ones. Considering the existing IceCube limit on the neutrino flux of
triggered GRBs, we find that the total flux of triggered and untriggered GRBs
can reach at most a level of ~10^-9 GeV cm^-2 s^-1 sr^-1, which is insufficient
to account for the reported two PeV neutrinos. Possible contributions to
diffuse neutrinos by low-luminosity GRBs and the earliest population of GRBs
are also discussed.Comment: Accepted by ApJ, one more figure added to show the contribution to
the diffuse neutrino flux by untriggered GRBs with different luminosity,
results and conclusions unchange
On the origin of >10 GeV photons in gamma-ray burst afterglows
Fermi/LAT has detected long-lasting high-energy photons (>100 MeV) from
gamma-ray bursts (GRBs), with the highest energy photons reaching about 100
GeV. One proposed scenario is that they are produced by high-energy electrons
accelerated in GRB forward shocks via synchrotron radiation. We study the
maximum synchrotron photon energy in this scenario, considering the properties
of the microturbluence magnetic fields behind the shock, as revealed by recent
Particle-in-Cell simulations and theoretical analyses of relativistic
collisionless shocks. Due to the small-scale nature of the micro-turbulent
magnetic field, the Bohm acceleration approximation breaks down at such high
energies. This effect leads to a typical maximum synchrotron photon of a few
GeV at 100 s after the burst and this maximum synchrotron photon energy
decreases quickly with time. We show that the fast decrease of the maximum
synchrotron photon energy leads to a fast decay of the synchrotron flux. The
10-100 GeV photons detected after the prompt phase can not be produced by the
synchrotron mechanism. They could originate from the synchrotron self-Compton
emission of the early afterglow if the circum-burst density is sufficiently
large, or from the external inverse-Compton process in the presence of central
X-ray emission, such as X-ray flares and prompt high-latitude X-ray emission.Comment: 13 pages, 3 figures, accepted by ApJ Letter
Understanding the multiwavelength observation of Geminga's TeV halo: the role of anisotropic diffusion of particles
In this letter we propose that the X-ray and the TeV observations in the
vicinity of Geminga can be understood in the framework of anisotropic diffusion
of injected electrons/positrons. This interpretation only requires the
turbulence in the vicinity of Geminga to be sub-Alfv\'enic with the local mean
magnetic field direction approximately aligned with our line of sight towards
Geminga, without invoking extreme conditions for the environment, such as an
extremely small diffusion coefficient and a weak magnetic field of strength
G as suggested in previous literature.Comment: 7 pages, 4 figures, including Supplemental Material, PRL accepte
How far are the sources of IceCube neutrinos? Constraints from the diffuse TeV gamma-ray background
The nearly isotropic distribution of the TeV-PeV neutrinos recently detected
by IceCube suggests that they come from sources at distance beyond our Galaxy,
but how far they are is largely unknown due to lack of any associations with
known sources. In this paper, we propose that the cumulative TeV gamma-ray
emission accompanying the production of neutrinos can be used to constrain the
distance of these neutrino sources, since the opacity of TeV gamma rays due to
absorption by the extragalactic background light (EBL) depends on the distance
that these TeV gamma rays have travelled. As the diffuse extragalactic TeV
background measured by \emph{Fermi} is much weaker than the expected cumulative
flux associated with IceCube neutrinos, the majority of IceCube neutrinos, if
their sources are transparent to TeV gamma rays, must come from distances
larger than the horizon of TeV gamma rays. We find that above 80\% of the
IceCube neutrinos should come from sources at redshift . Thus, the
chance for finding nearby sources correlated with IceCube neutrinos would be
small. We also find that, to explain the flux of neutrinos under the TeV
gamma-ray emission constraint, the redshift evolution of neutrino source
density must be at least as fast as the the cosmic star-formation rate.Comment: Accepted by ApJ, some minor changes made, 8 pages, 5 figure
Interpretation of the unprecedentedly long-lived high-energy emission of GRB 130427A
High energy photons (>100 MeV) are detected by the Fermi/LAT from GRB 130427A
up to almost one day after the burst, with an extra hard spectral component
being discovered in the high-energy afterglow. We show that this hard spectral
component arises from afterglow synchrotron-self Compton emission. This
scenario can explain the origin of >10 GeV photons detected up to ~30000s after
the burst, which would be difficult to be explained by synchrotron radiation
due to the limited maximum synchrotron photon energy. The lower energy
multi-wavelength afterglow data can be fitted simultaneously by the afterglow
synchrotron emission. The implication of detecting the SSC emission for the
circumburst environment is discussed.Comment: 4 pages, 2 figures, ApJL in pres
Evidence of an Internal Dissipation Origin for the High-energy Prompt Emission of GRB 170214A
The origin of the prompt high-energy (MeV) emission of Gamma-ray Bursts
(GRBs), detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray
Space Telescope, is still under debate, for which both the external shock
origin and internal dissipation origin have been suggested. In the internal
dissipation scenario, the high energy emission is expected to exhibit
significant temporal variability, tracking the keV/MeV fast variable behavior.
Here, we report a detailed analysis on the Fermi data of GRB~170214A, which is
sufficiently bright in the high energy to enable a quantitative analysis of the
correlation between high-energy emission and keV/MeV emission with high
statistics. Our result shows a clear temporal correlation between high-energy
and keV/MeV emission in the whole prompt emission phase as well as in two
decomposed short time intervals. Such correlation behavior is also found in
some other bright LAT GRBs, i.e., GRB 080916C, 090902B and 090926A. For these
GRBs as well as GRB 090510, we also find the rapid temporal variability in the
high-energy emission. We thus conclude that the prompt high-energy emission in
these bright LAT GRBs should be due to internal origin.Comment: 12 pages, 4 figures, Accepted for publication in Ap
Applicability of Relativistic Point-Coupling Models to Neutron Star Physics
Comparing with a wide range of covariant energy density functional models
based on the finite-range meson-exchange representation, the relativistic
mean-field models with the zero-range contact interaction, namely the
relativistic point-coupling models, are still infrequent to be utilized in
establishing nuclear equation of state (EoS) and investigating neutron star
properties, although comprehensive applications and achievements of them in
describing many nuclear properties both in ground and exited states are mature.
In this work, the EoS of neutron star matter is established constructively in
the framework of the relativistic point-coupling models to study neutron star
physics. Taking two selected functionals DD-PC1 and PC-PK1 as examples, nuclear
symmetry energies and several neutron star properties including proton
fractions, mass-radius relations, the core-crust transition density, the
fraction of crustal moment of inertia and dimensionless tidal deformabilities
are discussed. A suppression of pressure of neutron star matter found in the
functional PC-PK1 at high densities results in the difficulty of its prediction
when approaching to the maximum mass of neutron stars. In addition, the
divergences between two selected functionals in describing neutron star
quantities mentioned above are still large, ascribing to the less constrained
behavior of these functionals at high densities. Then it is expected that the
constraints on the dense matter EoS from precise and massive modern
astronomical observations, such as the tidal-deformabilities taken from
gravitational-wave events, would be essential to improve the parameterizing of
the relativistic point-coupling models.Comment: To appear in the AIP Proceedings of the Xiamen-CUSTIPEN Workshop on
the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave
Astronomy, Jan. 3-7, Xiamen, Chin
- …