1,800 research outputs found
Comment on 'Helmholtz theorem and the v-gauge in the problem of superluminal and instantaneous signals in classical electrodynamics,' by Chubykalo et al [Found. of Phys. Lett, 19, 37-46 (2006)]
Fundamental errors in the Chubykalo et al paper [Found. of Phys. Lett, 19,
37-46 (2006)] are highlighted. Contrary to their claim that "... the
irrotational component of the electric field has a physical meaning and can
propagate exclusively instantaneously," it is shown that this instantaneous
component is physically irrelevant because it is always canceled by a term
contained into the solenoidal component. This result follows directly from the
solution of the wave equation that satisfies the solenoidal component.
Therefore the subsequent inference of these authors that there are two
mechanisms of transmission of energy and momentum in classical electrodynamics,
one retarded and the other one instantaneous, has no basis. The example given
by these authors in which the full electric field of an oscillating charge
equals its instantaneous irrotational component on the axis of oscillations is
proved to be false.Comment: An alternative discussion can be found in the paper: Jose A. Heras,
"How potentials in different gauges yield the same retarded electric and
magnetic fields," Am. J. Phys. 75, 176-183 (2007
A short proof that the Coulomb-gauge potentials yield the retarded fields
A short demonstration that the potentials in the Coulomb gauge yield the
retarded electric and magnetic fields is presented. This demonstration is
relatively simple and can be presented in an advanced undergraduate curse of
electromagnetic theory
Preacceleration without radiation: the non-existence of preradiation phenomenon
An unexpected prediction of classical electrodynamics is that a charge can
accelerate before a force is applied. We would expect that a preaccelerated
charge would radiate so that there would be spontaneous preradiation, an
acausal phenomenon. We reexamine the subtle relation between the Larmor formula
for the power radiated by a point charge and the Abraham-Lorentz equation and
find that for well-behaved external forces acting for finite times, the charge
does not radiate in time intervals where there is preacceleration. That is, for
these forces preradiation does not exist even though the charge is
preaccelerated. The radiative energy is emitted only in time intervals when the
external force acts on the charge.Comment: Equation (37) of the published paper in AJP has been correcte
Reply to "Comment(s) on `Preacceleration without radiation: The non-existence of preradiation phenomenon," by J. D. Jackson [Am. J. Phys. 75, 844-845 (2007)] and V. Hnizdo [Am. J. Phys. 75, 845-846 (2007)
This paper replies the comments by J. D. Jackson [Am. J. Phys. 75, 844-845
(2007)] and V. Hnizdo [Am. J. Phys. 75, 845-846 (2007)].Comment: 9 pages. See also the related paper: "E. Eriksen and O. Gron, Does
preradiation exist? [Phys. Scr. 76, 60-63 (2007)].
A search for near infrared counterparts of 3 pulsar wind nebulae
While pulsar wind nebulae (PWNe) and their associated isolated pulsars are
commonly detected at X-ray energies, they are much rarer at near infrared (nIR)
and optical wavelengths. Here we examine three PWN systems in the Galactic
plane - IGR J14003-6326, HESS J1632-478 and IGR J18490-0000 - in a bid to
identify optical/nIR emission associated with either the extended PWNe or their
previously detected X-ray point sources. We obtain optical/nIR images of the
three fields with the ESO - New Technology Telescope and apply standard
photometric and astrometric calibrations. We find no evidence of any extended
emission associated with the PWNe in any of the fields; neither do we find any
new counterparts to the X-ray point sources, except to confirm the magnitude of
the previously identified counterpart candidate of IGR J18490-0000. Further
observations are required to confirm the association of the nIR source to IGR
J18490-0000 and to detect counterparts to IGR J14003-6326 and HESS J1632-478,
while a more accurate X-ray position is required to reduce the probability of a
chance superposition in the field of the latter.Comment: Accepted to A&A (4 pages, 1 figure
Generalization of the Schott energy in electrodynamic radiation theory
We discuss the origin of the Schott energy in the Abraham-Lorentz version of
electrodynamic radiation theory and how it can be used to explain some apparent
paradoxes. We also derive the generalization of this quantity for the
Ford-O'Connell equation, which has the merit of being derived exactly from a
microscopic Hamiltonian for an electron with structure and has been shown to be
free of the problems associated with the Abraham-Lorentz theory. We emphasize
that the instantaneous power supplied by the applied force not only gives rise
to radiation (acceleration fields), but it can change the kinetic energy of the
electron and change the Schott energy of the velocity fields. The important
role played by boundary conditions is noted
Instantaneous fields in classical electrodynamics
In this paper we express the retarded fields of Maxwell's theory in terms of the instantaneous fields of a Galilei-invariant electromagnetic and we find the vector function whose spatial and temporal derivatives transform the instantaneous fields into the retarded ones. We conclude that the instantaneous fields can formally be introduced as unphysical objects into classical electrodynamics which can be used to find the physical retarded fields
The nature of the X-ray binary IGR J19294+1816 from INTEGRAL, RXTE, and Swift observations
We report the results of a high-energy multi-instrumental campaign with
INTEGRAL, RXTE, and Swift of the recently discovered INTEGRAL source IGR
J19294+1816. The Swift/XRT data allow us to refine the position of the source
to RA= 19h 29m 55.9s Dec=+18deg 18' 38.4" (+- 3.5"), which in turn permits us
to identify a candidate infrared counterpart. The Swift and RXTE spectra are
well fitted with absorbed power laws with hard (Gamma ~ 1) photon indices.
During the longest Swift observation, we obtained evidence of absorption in
true excess to the Galactic value, which may indicate some intrinsic absorption
in this source. We detected a strong (P=40%) pulsation at 12.43781 (+-0.00003)
s that we interpret as the spin period of a pulsar. All these results, coupled
with the possible 117 day orbital period, point to IGR J19294+1816 being an
HMXB with a Be companion star. However, while the long-term INTEGRAL/IBIS/ISGRI
18--40 keV light curve shows that the source spends most of its time in an
undetectable state, we detect occurrences of short (~2000-3000 s) and intense
flares that are more typical of supergiant fast X-ray transients. We therefore
cannot make firm conclusions on the type of system, and we discuss the possible
implications of IGR J19294+1816 being an SFXT.Comment: 7 pages, 6 figures, accepted for publication in A&
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