2,491 research outputs found
Improving the Convergence of an Iterative Algorithm Proposed By Waxman
In the iterative algorithm recently proposed by Waxman for solving eigenvalue
problems, we point out that the convergence rate may be improved. For many
non-singular symmetric potentials which vanish asymptotically, a simple
analytical relationship between the coupling constant of the potential and the
ground state eigenvalue is obtained which can be used to make the algorithm
more efficient
Neutral beam model for the anomalous gamma-ray emission component in GRB 941017
Gonz\'alez et al. (2003) have reported the discovery of an anomalous
radiation component from ~ 1 -- 200 MeV in GRB 941017. This component varies
independently of and contains > 3 times the energy found in the prompt ~ 50 keV
-- 1 MeV radiation component that is well described by the relativistic
synchrotron-shock model. Acceleration of hadrons to very high energies can give
rise to two additional emission components, one produced inside the GRB blast
wave and one associated with an escaping beam of ultra-high energy (UHE; >
10^{14} eV) neutrons, gamma rays, and neutrinos. The first component extending
to ~ 100 MeV is from a pair-photon cascade induced by photomeson processes with
the internal synchrotron photons coincident with the prompt radiation. The
outflowing UHE neutral beam can undergo further interactions with external
photons from the backscattered photon field to produce a beam of
hyper-relativistic electrons that lose most of their energy during a fraction
of a gyroperiod in the assumed Gauss-strength magnetic fields of the
circumburst medium. The synchrotron radiation of these electrons has a spectrum
with vF_v index equal to +1 that can explain the anomalous component in GRB
941017. This interpretation of the spectrum of GRB 941017 requires a high
baryon load of the accelerated particles in GRB blast waves. It implies that
most of the radiation associated with the anomalous component is released at >
500 MeV, suitable for observations with GLAST, and with a comparable energy
fluence in ~100 TeV neutrinos that could be detected with a km-scale neutrino
telescope like IceCube.Comment: 4 pages, 1 figure, minor corrections, Astronomy and Astrophysics
Letters, in pres
Efficiency and spectrum of internal gamma-ray burst shocks
We present an analysis of the Internal Shock Model of GRBs, where gamma-rays
are produced by internal shocks within a relativistic wind. We show that
observed GRB characteristics impose stringent constraints on wind and source
parameters. We find that a significant fraction, of order 20 %, of the wind
kinetic energy can be converted to radiation, provided the distribution of
Lorentz factors within the wind has a large variance and provided the minimum
Lorentz factor is higher than 10^(2.5)L_(52)^(2/9), where L=10^(52)L_(52)erg/s
is the wind luminosity. For a high, >10 %, efficiency wind, spectral energy
breaks in the 0.1 to 1 MeV range are obtained for sources with dynamical time
R/c < 1 ms, suggesting a possible explanation for the observed clustering of
spectral break energies in this range. The lower limit to wind Lorenz factor
and the upper limit, around (R/10^7 cm)^(-5/6) MeV to observed break energies
are set by Thomson optical depth due to electron positron pairs produced by
synchrotron photons. Natural consequences of the model are absence of bursts
with peak emission energy significantly exceeding 1 MeV, and existence of low
luminosity bursts with low, 1 keV to 10 keV, break energies.Comment: 10 pages, 5 ps-figures. Expanded discussion of magnetic field and
electron energy fraction. Accepted for publication in Astrophysical Journa
Neutrino flux predictions for known Galactic microquasars
It has been proposed recently that Galactic microquasars may be prodigious
emitters of TeV neutrinos that can be detected by upcoming km^2 neutrino
telescopes. In this paper we consider a sample of identified microquasars and
microquasar candiates, for which available data enables rough determination of
the jet parameters. By employing the parameters inferred from radio
observations of various jet ejection events, we determine the neutrino fluxes
that should have been produced during these events by photopion production in
the jet. Despite the large uncertainties in our analysis, we demonstrate that
in several of the sources considered, the neutrino flux at Earth, produced in
events similar to those observed, would exceed the detection threshold of a
km^2 neutrino detector. The class of microquasars may contain also sources with
bulk Lorentz factors larger than those characteristic of the sample considered
here, directed along our line of sight. Such sources, which may be very
difficult to resolve at radio wavelengths and hence may be difficult to
identify as microqusar candidates, may emit neutrinos with fluxes significantly
larger than typically obtained in the present analysis. These sources may
eventually be identified through their neutrino and gamma-ray emission.Comment: 17 pages. Submitted to Ap
The Gradient Expansion for the Free-Energy of a Clean Superconductor
We describe a novel method for obtaining the gradient expansion for the free
energy of a clean BCS superconductor. We present explicit results up to fourth
order in the gradients of the order parameter.Comment: 33 pages, Late
On the Absence of Spurious Eigenstates in an Iterative Algorithm Proposed By Waxman
We discuss a remarkable property of an iterative algorithm for eigenvalue
problems recently advanced by Waxman that constitutes a clear advantage over
other iterative procedures. In quantum mechanics, as well as in other fields,
it is often necessary to deal with operators exhibiting both a continuum and a
discrete spectrum. For this kind of operators, the problem of identifying
spurious eigenpairs which appear in iterative algorithms like the Lanczos
algorithm does not occur in the algorithm proposed by Waxman
No Radio Afterglow from the Gamma-Ray Burst of February 28, 1997
We present radio observations of the gamma-ray burster GRB 970228 made with
the Very Large Array (VLA) and the Owens Valley Radio Observatory (OVRO)
spanning a range of postburst timescales from one to 300 days. A search for a
time-variable radio source was conducted covering an area which included a
fading X-ray source and an optical transient, both of which are thought to be
the long wavelength counterparts to the gamma-ray burst. At the position of the
optical transient sensitive limits between 10 uJy and 1 mJy can be placed on
the absence of a radio counterpart to GRB 970228 between 1.4 and 240 GHz. We
apply a simple formulation of a fireball model which has been used with some
success to reproduce the behavior of the optical and X-ray light curves. Using
this model we conclude that the radio non-detections are consistent with the
peak flux density of the afterglow lying between 20-40 uJy and it requires that
the optical flux peaked between 4 and 16 hours after the burst.Comment: ApJ Let (submitted
No Contest? An Analysis of the Legality of Thoroughbred Handicapping Contests under Conflicting State Law Regimes
Extra galactic sources of high energy neutrinos
The main goal of the construction of large volume, high energy neutrino
telescopes is the detection of extra-Galactic neutrino sources. The existence
of such sources is implied by observations of ultra-high energy, >10^{19} eV,
cosmic-rays (UHECRs), the origin of which is a mystery. The observed UHECR flux
sets an upper bound to the extra-Galactic high energy neutrino intensity, which
implies that the detector size required to detect the signal in the energy
range of 1 TeV to 1 PeV is >=1 giga-ton, and much larger at higher energy.
Optical Cerenkov neutrino detectors, currently being constructed under ice and
water, are expected to achieve 1 giga-ton effective volume for 1 TeV to 1 PeV
neutrinos. Coherent radio Cerenkov detectors (and possibly large air-shower
detectors) will provide the >> 1 giga-ton effective volume required for
detection at ~10^{19} eV. Detection of high energy neutrinos associated with
electromagnetically identified sources will allow to identify the sources of
UHECRs, will provide a unique probe of the sources, which may allow to resolve
open questions related to the underlying physics of models describing these
powerful accelerators, and will provide information on fundamental neutrino
properties.Comment: 8 pages, 4 figures; Summary of talk presented at the Nobel Symposium
129: Neutrino Physics, Sweden 200
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