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 $Z_2\times Z_2'$ 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 $Z_2$ 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 $10\ \rm GeV \le M_{DM}\le 2000$ 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