40 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
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
Radio Detection of Green Peas: Implications for Magnetic Fields in Young Galaxies
Green Peas are a new class of young, emission line galaxies that were
discovered by citizen volunteers in the Galaxy Zoo project. Their low stellar
mass, low metallicity and very high star formation rates make Green Peas the
nearby (z~0.2) analogs of the Lyman-break Galaxies (LBGs) which account for the
bulk of the star formation in the early universe (z~2-5). They thus provide
accessible laboratories in the nearby Universe for understanding star
formation, supernova feedback, particle acceleration and magnetic field
amplification in early galaxies. We report the first direct radio detection of
Green Peas with low frequency GMRT observations and our stacking detection with
archival VLA FIRST data. We show that the radio emission implies that these
extremely young galaxies already have magnetic fields (>30 muG) even larger
than that of the Milky Way. This is at odds with the present understanding of
magnetic field growth based on amplification of seed fields by dynamo action
over a galaxy's lifetime. Our observations strongly favor models with
pregalactic magnetic fields at muG levels.Comment: 5 pages, 3 figures, 1 table, submitte
A new Tolman test of a cosmic distance duality relation at 21 cm
Under certain general conditions in an expanding universe, the luminosity
distance (d_L) and angular diameter distance (d_A) are connected by the
Etherington relation as d_L = d_A (1 + z)^2. The Tolman test suggests the use
of objects of known surface brightness, to test this relation. In this letter,
we propose the use of redshifted 21 cm signal from disk galaxies, where neutral
hydrogen (HI) masses are seen to be almost linearly correlated with surface
area, to conduct a new Tolman test. We construct simulated catalogs of
galaxies, with the observed size-luminosity relation and realistic redshift
evolution of HI mass functions, likely to be detected with the planned Square
Kilometer Array (SKA). We demonstrate that these observations may soon provide
the best implementation of the Tolman test to detect any violation of the
Etherington relation.Comment: 4 pages, 2 figures, 1 table, v2: published versio
Baryon Loaded Relativistic Blastwaves in Supernovae
We provide a new analytic blastwave solution which generalizes the
Blandford-McKee solution to arbitrary ejecta masses and Lorentz factors. Until
recently relativistic supernovae have been discovered only through their
association with long duration Gamma Ray Bursts (GRB). 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, as the ejecta mass is negligible in comparison to the swept
up mass. The recent discovery of the relativistic supernova SN 2009bb, without
a detected GRB, opens up 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 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 compute the synchrotron emission from
relativistic electrons in the shock amplified magnetic field. This models the
radio emission from the circumstellar interaction of a CEDEX. 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. We discuss the effect of baryon loading on the dynamics and
observational manifestations of a CEDEX. In particular, our predicted angular
size of SN 2009bb is consistent with VLBI upper limits on day 85, but is
presently resolvable on VLBI angular scales, since the relativistic ejecta is
still in the nearly free expansion phase.Comment: 13 pages, 6 figures, Accepted for publication in Ap