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A possible Macronova in the late afterglow of the `long-short' burst GRB 060614
Long-duration ( s) -ray bursts that are believed to originate
from the death of massive stars are expected to be accompanied by supernovae.
GRB 060614, that lasted 102 s, lacks a supernova-like emission down to very
stringent limits and its physical origin is still debated. Here we report the
discovery of near-infrared bump that is significantly above the regular
decaying afterglow. This red bump is inconsistent with even the weakest known
supernova. However, it can arise from a Li-Paczy\'{n}ski macronova the
radioactive decay of debris following a compact binary merger. If this
interpretation is correct GRB 060614 arose from a compact binary merger rather
than from the death of a massive star and it was a site of a significant
production of heavy r-process elements. The significant ejected mass favors a
black hole-neutron star merger but a double neutron star merger cannot be ruled
out.Comment: Minor revision; The version published in Nature Communication
Effects of Contrarians in the Minority Game
We study the effects of the presence of contrarians in an agent-based model
of competing populations. Contrarians are common in societies. These
contrarians are agents who deliberately prefer to hold an opinion that is
contrary to the prevailing idea of the commons or normal agents. Contrarians
are introduced within the context of the Minority Game (MG), which is a binary
model for an evolving and adaptive population of agents competing for a limited
resource. Results of numerical simulations reveal that the average success rate
among the agents depends non-monotonically on the fraction of
contrarians. For small , the contrarians systematically outperform the
normal agents by avoiding the crowd effect and enhance the overall success
rate. For high , the anti-persistent nature of the MG is disturbed and
the few normal agents outperform the contrarians. Qualitative discussion and
analytic results for the small and high regimes are also
presented, and the crossover behavior between the two regimes is discussed.Comment: revtex, 11 pages, 4 figure
GRB 120729A: External Shock Origin for Both the Prompt Gamma-Ray Emission and Afterglow
Gamma-ray burst (GRB) 120729A was detected by Swift/BAT and Fermi/GBM, and then rapidly observed by Swift/XRT, Swift/UVOT, and ground-based telescopes. It had a single long and smooth \gamma-ray emission pulse, which extends continuously to the X-rays. We report Lick/KAIT observations of the source, and make temporal and spectral joint fits of the multiwavelength light curves of GRB 120729A. It exhibits achromatic light-curve behavior, consistent with the predictions of the external shock model. The light curves are decomposed into four typical phases: onset bump (Phase I), normal decay (Phase II), shallow decay (Phase III), and post-jet break (Phase IV). The spectral energy distribution (SED) evolves from prompt \gamma-ray emission to the afterglow with photon index from Γγ=1.36 to Γ≈1.75. There is no obvious evolution of the SED during the afterglow. ...(Please see article full tet for complete abstract.
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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45099/1/10626_2005_Article_1570.pd
Plasmoid ejection and secondary current sheet generation from magnetic reconnection in laser-plasma interaction
Reconnection of the self-generated magnetic fields in laser-plasma
interaction was first investigated experimentally by Nilson {\it et al.} [Phys.
Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a
solid target layer. An elongated current sheet (CS) was observed in the plasma
between the two laser spots. In order to more closely model magnetotail
reconnection, here two side-by-side thin target layers, instead of a single
one, are used. It is found that at one end of the elongated CS a fan-like
electron outflow region including three well-collimated electron jets appears.
The ( MeV) tail of the jet energy distribution exhibits a power-law
scaling. The enhanced electron acceleration is attributed to the intense
inductive electric field in the narrow electron dominated reconnection region,
as well as additional acceleration as they are trapped inside the rapidly
moving plasmoid formed in and ejected from the CS. The ejection also induces a
secondary CS
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