9,108 research outputs found
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
Quantum Phase Transition in the Sub-Ohmic Spin-Boson Model: Extended Coherent-state Approach
We propose a general extended coherent state approach to the qubit (or
fermion) and multi-mode boson coupling systems. The application to the
spin-boson model with the discretization of a bosonic bath with arbitrary
continuous spectral density is described in detail, and very accurate solutions
can be obtained. The quantum phase transition in the nontrivial sub-Ohmic case
can be located by the fidelity and the order-parameter critical exponents for
the bath exponents can be correctly given by the fidelity
susceptibility, demonstrating the strength of the approach.Comment: 4 pages, 3 figure
Quantum phase transitions in coupled two-level atoms in a single-mode cavity
The dipole-coupled two-level atoms(qubits) in a single-mode resonant cavity
is studied by extended bosonic coherent states. The numerically exact solution
is presented. For finite systems, the first-order quantum phase transitions
occur at the strong interatomic interaction. Similar to the original Dicke
model, this system exhibits a second-order quantum phase transition from the
normal to the superradiant phases. Finite-size scaling for several observables,
such as the average fidelity susceptibility, the order parameter, and
concurrence are performed for different interatomic interactions. The obtained
scaling exponents suggest that interatomic interactions do not change the
universality class.Comment: 13 pages, 5 figure
- …