4,801 research outputs found
Engine-driven Relativistic Supernovae as Sources of Ultra High Energy Cosmic Rays
Understanding the origin of the highest energy cosmic rays is a crucial step
in probing new physics at energies unattainable by terrestrial accelerators.
Their sources remain an enigma half a century after their discovery. They must
be accelerated in the local universe as otherwise interaction with cosmic
background radiations would severely deplete the flux of protons and nuclei at
energies above the Greisen-Zatsepin-Kuzmin (GZK) limit. Hypernovae, nearby
GRBs, AGNs and their flares have all been suggested and debated in the
literature as possible sources. Type Ibc supernovae have a local sub-population
with mildly relativistic ejecta which are known to be sub-energetic GRBs or
X-Ray Flashes for sometime and more recently as those with radio afterglows but
without detected GRB counterparts, such as SN 2009bb. In this work we measure
the size-magnetic field evolution, baryon loading and energetics of SN 2009bb
using its radio spectra obtained with VLA and GMRT. We show that the
engine-driven SNe lie above the Hillas line and they can explain the
characteristics of post-GZK UHECRs.Comment: 4 pages, 1 figure, proceedings of the GRB 2010 conference in
Annapolis, US
Interplay of Scalar and Fermionic Components in a Multi-component Dark Matter Scenario
We explore the multi-component dark matter (DM) scenario considered in a
simple extension of the standard model with an inert scalar doublet and a
singlet fermionic field providing the two DM candidates. The DM states are made
stable under the unbroken discrete symmetry. An additional
gauge singlet scalar field is introduced to facilitate the interaction of the
dark fermion with the visible sector. Presence of a charged fermionic field
having the same charge as that of the inert scalar field allows exploring
the dark matter mass regions otherwise disallowed, like in the standard Inert
Doublet Model (IDM) scenarios. With these arrangements, it is shown that the
light DM scenario and the desert region in the intermediate mass range of DM in
the standard IDM case can be made compatible with the relic density bounds and
direct detection limits. Further, detailed parameter space study is carried out
keeping the coexistence of both the scalar and fermionic components in focus,
showing that sizable parameter space regions are available for the entire mass
range of GeV.Comment: 19 pages, 19 figures, appendix added, some minor corrections to main
tex
Afterglows of Mildly Relativistic Supernovae: Baryon Loaded Blastwaves
Relativistic supernovae have been discovered until recently only through
their association with long duration Gamma Ray Bursts (GRB). As the ejecta mass
is negligible in comparison to the swept up mass, the blastwaves of such
explosions are well described by the Blandford-McKee (in the ultra relativistic
regime) and Sedov-Taylor (in the non-relativistic regime) solutions during
their afterglows. However, the recent discovery of the relativistic supernova
SN 2009bb, without a detected GRB, has indicated the possibility of highly
baryon loaded mildly relativistic outflows which remains in nearly free
expansion phase during the radio afterglow. In this work, we consider the
dynamics and emission from a massive, relativistic shell, launched by a Central
Engine Driven EXplosion (CEDEX), decelerating adiabatically due to its
collision with the pre-explosion circumstellar wind profile of the progenitor.
We show that this model explains the observed radio evolution of the
prototypical SN 2009bb and demonstrate that SN 2009bb had a highly baryon
loaded, mildly relativistic outflow.Comment: 4 pages, 2 figure, proceedings of the GRB 2010 conference in
Annapolis, US
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