817 research outputs found
Constraining the Cosmic Star Formation Rate with the MeV Background
The Cosmic Gamma-ray Background (CGB) in the MeV regime has been measured
with COMPTEL and SMM. The origin of the CGB in this energy regime is believed
to be dominated by gamma-rays from Type Ia supernovae. We calculate the CGB
spectrum within the framework of FRW cosmology as a function of the cosmic star
formation rate, SFR(z). Several estimates of the SFR(z) have been reported
since the pioneering work of Madau et al. Here we discuss observational
constraints on SFR(z) derived from models of the CGB. In particular, we
consider the SFR obtained from Gamma-Ray Burst observations, which increases
dramatically with redshift beyond z ~ 1 in contrast to most estimates which
saturate or show a mild increase with redshift. Gamma-ray bursts may be the
most powerful tracers of star formation in the early universe and thus provide
signposts of the initial epoch of element synthesis. The star formation rate
implied by GRB statistics results in a gamma-ray background that matches the
observations more closely than that inferred from other tracers of star
formation. This may provide some support for the GRB/SFR-paradigm, which in
turn promises a powerful diagnostic of star formation, and thus cosmic chemical
evolution, from the era of Population III stars to the present
Magnetohydrodynamic Effects in Propagating Relativistic Ejecta: Reverse Shock and Magnetic Acceleration
We solve the Riemann problem for the deceleration of arbitrarily magnetized relativistic ejecta injected into a static unmagnetized medium. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization s (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when s exceeds a critical value, sc, defined by the balance between the magnetic pressure in the ejecta and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly larger than the initial value. This acceleration mechanism is due to the strong magnetic pressure in the ejecta
Higher order curvature generalisations of Bartnick-McKinnon and coloured black hole solutions in
We construct globally regular as well as non-abelian black hole solutions of
a higher order curvature Einstein-Yang-Mills (EYM) model in dimensions.
This model consists of the superposition of the first two members of the
gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with
the superposition of the first two members of the Yang--Mills
hierarchy.Comment: 13 Revtex pages, 5 PS figures; discussions extended, reference adde
Rotating regular solutions in Einstein-Yang-Mills-Higgs theory
We construct new axially symmetric rotating solutions of
Einstein-Yang-Mills-Higgs theory. These globally regular configurations possess
a nonvanishing electric charge which equals the total angular momentum, and
zero topological charge, representing a monopole-antimonopole system rotating
around the symmetry axis through their common center of mass.Comment: 7 pages, 4 figures: misprints correcte
The Supernova Relic Neutrino Background
An upper bound to the supernova relic neutrino background from all past Type
II supernovae is obtained using observations of the Universal metal enrichment
history. We show that an unambiguous detection of these relic neutrinos by the
Super-Kamiokande detector is unlikely. We also analyze the event rate in the
Sudbury Neutrino Observatory (where coincident neutrons from anti-nu_e + D -->
n + n + e+ might enhance background rejection), and arrive at the same
conclusion. If the relic neutrino flux should be observed to exceed our upper
bound and if the observations of the metal enrichment history (for z<1) are not
in considerable error, then either the Type II supernova rate does not track
the metal enrichment history or some mechanism may be responsible for
transforming anti-nu_{mu,tau} --> anti-nu_e.Comment: Matches version accepted for publication in Phys. Rev.
Scaling analysis of a divergent prefactor in the metastable lifetime of a square-lattice Ising ferromagnet at low temperatures
We examine a square-lattice nearest-neighbor Ising quantum ferromagnet
coupled to -dimensional phonon baths. Using the density-matrix equation, we
calculate the transition rates between configurations, which determines the
specific dynamic. Applying the calculated stochastic dynamic in Monte Carlo
simulations, we measure the lifetimes of the metastable state. As the magnetic
field approaches at low temperatures, the lifetime prefactor diverges
because the transition rates between certain configurations approaches zero
under these conditions. Near and zero temperature, the divergent
prefactor shows scaling behavior as a function of the field, temperature, and
the dimension of the phonon baths. With proper scaling, the simulation data at
different temperatures and for different dimensions of the baths collapse well
onto two master curves, one for and one for .Comment: published versio
Prospects of gravitational-wave follow-up through a wide-field ultraviolet satellite: A Dorado case study
The detection of gravitational waves from the binary neuron star merger GW170817 and electromagnetic counterparts GRB170817A and AT2017gfo kick-started the field of gravitational-wave multimessenger astronomy. The optically red to near-infrared emission ("red" component) of AT2017gfo was readily explained as produced by the decay of newly created nuclei produced by rapid neutron capture (a kilonova). However, the ultraviolet to optically blue emission ("blue" component) that was dominant at early times (up to 1.5 days) received no consensus regarding its driving physics. Among many explanations, two leading contenders are kilonova radiation from a lanthanide-poor ejecta component and shock interaction (cocoon emission). In this work, we simulate AT2017gfo-like light curves and perform a Bayesian analysis to study whether an ultraviolet satellite capable of rapid gravitational-wave follow-up, could distinguish between physical processes driving the early "blue" component. We find that ultraviolet data starting at 1.2 hr distinguishes the two early radiation models up to 160 Mpc, implying that an ultraviolet mission like Dorado would significantly contribute to insights into the driving emission physics of the postmerger system. While the same ultraviolet data and optical data starting at 12 hr have limited ability to constrain model parameters separately, the combination of the two unlocks tight constraints for all but one parameter of the kilonova model up to 160 Mpc. We further find that a Dorado-like ultraviolet satellite can distinguish the early radiation models up to at least 130 (60) Mpc if data collection starts within 3.2 (5.2) hr for AT2017gfo-like light curves
The host galaxy of the short GRB 050709
The host of the short gamma-ray burst (GRB) 050709 is a morphologically disturbed low-luminous galaxy. At a redshift of z = 0.16, it belongs to one of the cosmologically nearest short-GRB hosts identified to date. Consequently, it represents a promising target for sensitive, spatially resolved observational studies. We have used the Multi Unit Spectroscopic Explorer (MUSE) mounted at the Very Large Telescope to characterize the GRB host galaxy. In addition, we performed deep radio-continuum observations of the host with the Australia Telescope Compact Array (ATCA) and with ALMA at 1.3 mm. Moreover, we made use of archival Spitzer Space Telescope 24 μm and Hubble Space Telescope/F814W imaging data of this galaxy. The spatially resolved MUSE data reveal that the entire host is a source of strong line emission, in particular from Hα and [O II
Lyman continuum leakage in faint star-forming galaxies at redshift z = 3-3.5 probed by gamma-ray bursts
The polarization evolution of the optical afterglow of GRB 030329
We report 31 polarimetric observations of the afterglow of GRB 030329 with
high signal-to-noise and high sampling frequency. The data imply that the
afterglow magnetic field has small coherence length and is mostly random,
probably generated by turbulence.Comment: 2003 GRB Conference, Santa Fe, Oct. 2003, 1 ps-figur
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