3,996 research outputs found
Neutrinos from Early-Phase, Pulsar-Driven Supernovae
Neutron stars, just after their formation, are surrounded by expanding,
dense, and very hot envelopes which radiate thermal photons. Iron nuclei can be
accelerated in the wind zones of such energetic pulsars to very high energies.
These nuclei photo-disintegrate and their products lose energy efficiently in
collisions with thermal photons and with the matter of the envelope, mainly via
pion production. When the temperature of the radiation inside the envelope of
the supernova drops below K, these pions decay before
losing energy and produce high energy neutrinos. We estimate the flux of muon
neutrinos emitted during such an early phase of the pulsar - supernova envelope
interaction. We find that a 1 km neutrino detector should be able to detect
neutrinos above 1 TeV within about one year after the explosion from a
supernova in our Galaxy. This result holds if these pulsars are able to
efficiently accelerate nuclei to energies eV, as postulated
recently by some authors for models of Galactic acceleration of the extremely
high energy cosmic rays (EHE CRs).Comment: 16 pages, 3 figures, revised version submitted to Ap
Rings and Jets around PSR J2021+3651: the `Dragonfly Nebula'
We describe recent Chandra ACIS observations of the Vela-like pulsar PSR
J2021+3651 and its pulsar wind nebula (PWN). This `Dragonfly Nebula' displays
an axisymmetric morphology, with bright inner jets, a double-ridged inner
nebula, and a ~30" polar jet. The PWN is embedded in faint diffuse emission: a
bow shock-like structure with standoff ~1' brackets the pulsar to the east and
emission trails off westward for 3-4'. Thermal (kT=0.16 +/-0.02 keV) and power
law emission are detected from the pulsar. The nebular X-rays show spectral
steepening from Gamma=1.5 in the equatorial torus to Gamma=1.9 in the outer
nebula, suggesting synchrotron burn-off. A fit to the `Dragonfly' structure
suggests a large (86 +/-1 degree) inclination with a double equatorial torus.
Vela is currently the only other PWN showing such double structure. The >12 kpc
distance implied by the pulsar dispersion measure is not supported by the X-ray
data; spectral, scale and efficiency arguments suggest a more modest 3-4 kpc.Comment: 22 pages, 5 figures, 3 tables, Accepted to Ap
An analysis of gamma-ray burst spectral break models
Typical gamma-ray burst spectra are characterized by a spectral break, Ep,
which for bright BATSE bursts is found to be narrowly clustered around 300 keV.
Recently identified X-ray flashes, which may account for a significant portion
of the whole GRB population, seem to extend the Ep distribution to a broader
range below 40 keV. Positive correlations among Ep and some other observed
parameters have been noticed. On the other hand, within the cosmological
fireball model, the issues concerning the dominant energy ingredient of the
fireball as well as the location of the GRB emission site are still unsettled,
leading to several variants of the fireball model. Here we analyze these models
within a unified framework, and critically reexamine the Ep predictions in the
various model variants. Attention is focused on the predictions of the
narrowness of the Ep distribution in different models, and the correlations
among Ep and some other measurable observables. These model properties may be
tested against the current and upcoming GRB data, through which the nature of
the fireball as well as the mechanism and site of the GRB emission will be
identified. In view of the current data, various models are appraised through a
simple Monte-Carlo simulation, and a tentative discussion about the possible
nature of X-ray flashes is presented.Comment: 14 pages, 3 figures, emulateapj style, accepted for publication in
ApJ. Monte Carlo simulation added to allow a clearer comparison among the
model
Quantum black holes from null expansion operators
Using a recently developed quantization of spherically symmetric gravity
coupled to a scalar field, we give a construction of null expansion operators
that allow a definition of general, fully dynamical quantum black holes. These
operators capture the intuitive idea that classical black holes are defined by
the presence of trapped surfaces, that is surfaces from which light cannot
escape outward. They thus provide a mechanism for classifying quantum states of
the system into those that describe quantum black holes and those that do not.
We find that quantum horizons fluctuate, confirming long-held heuristic
expectations. We also give explicit examples of quantum black hole states. The
work sets a framework for addressing the puzzles of black hole physics in a
fully quantized dynamical setting.Comment: 5 pages, version to appear in CQ
ASCA observations of the young rotation-powered pulsars PSR B1046-58 and PSR B1610-50
We present X-ray observations of two young energetic radio pulsars, PSRs
B1046-58 and B1610-50, and their surroundings, using archival data from the
Advanced Satellite for Cosmology and Astrophysics (ASCA).
The energetic pulsar PSR B1046-58 is detected in X-rays with a significance
of 4.5 sigma. The unabsorbed flux, estimated assuming a power-law spectrum and
a neutral hydrogen column density N_H of 5E21 cm^-2 is (2.5 +/- 0.3) x 10E-13
ergs/cm^2/s in the 2-10 keV band. Pulsed emission is not detected; the pulsed
fraction is less than 31% at the 90% confidence level for a 50% duty cycle. We
argue that the emission is best explained as originating from a pulsar-powered
synchrotron nebula. The X-ray counterpart of the pulsar is the only hard source
within the 95% error region of the previously unidentified gamma-ray source 3EG
J1048-5840. This evidence supports the results of Kaspi et al. (1999), who in a
companion paper, suggest that PSR B1046-58 is the counterpart to 3EG
J1048-5840.
X-ray emission from PSR B1610-50 is not detected. Using similar assumptions
as above, the derived 3 sigma upper limit for the unabsorbed 2-10 keV X-ray
flux is 1.5E-13 ergs/cm^2/s. We use the flux limit to estimate the pulsar's
velocity to be less than ~170 km/s, casting doubt on a previously reported
association between PSR B1610-50 and supernova remnant Kes 32. Kes 32 is
detected, as is evident from the correlation between X-ray and radio emission.
The ASCA images of PSR B1610-50 are dominated by mirror-scattered emission from
the X-ray-bright supernova remnant RCW 103, located 33' away.
We find no evidence for extended emission around either pulsar, in contrast
to previous reports of large nebulae surrounding both pulsars.Comment: Accepted for publication in the ApJ (v.528, pp.436-444) Correcting
typo in abstract of .tex fil
The Gelfand map and symmetric products
If A is an algebra of functions on X, there are many cases when X can be
regarded as included in Hom(A,C) as the set of ring homomorphisms. In this
paper the corresponding results for the symmetric products of X are introduced.
It is shown that the symmetric product Sym^n(X) is included in Hom(A,C) as the
set of those functions that satisfy equations generalising f(xy)=f(x)f(y).
These equations are related to formulae introduced by Frobenius and, for the
relevant A, they characterise linear maps on A that are the sum of ring
homomorphisms. The main theorem is proved using an identity satisfied by
partitions of finite sets.Comment: 14 pages, Late
Modeling interaction of relativistic and nonrelativistic winds in binary system PSR 1259-63/SS2883. I.Hydrodynamical limit
In this paper, we present a detailed hydrodynamical study of the properties
of the flow produced by the collision of a pulsar wind with the surrounding in
a binary system. This work is the first attempt to simulate interaction of the
ultrarelativistic flow (pulsar wind) with the nonrelativistic stellar wind.
Obtained results show that the wind collision could result in the formation of
an "unclosed" (at spatial scales comparable to the binary system size) pulsar
wind termination shock even when the stellar wind ram pressure exceeds
significantly the pulsar wind kinetical pressure. Moreover, the post-shock flow
propagates in a rather narrow region, with very high bulk Lorentz factor
(). This flow acceleration is related to adiabatical losses,
which are purely hydrodynamical effects. Interestingly, in this particular
case, no magnetic field is required for formation of the ultrarelativistic bulk
outflow. The obtained results provide a new interpretation for the orbital
variability of radio, X-ray and gamma-ray signals detected from binary pulsar
system PSR 1259-63/SS2883.Comment: 11 pages, 13 figures, submitted to MNRA
Gamma-Ray Emission from PWNe Interacting with Molecular Clouds
We consider a situation in which a pulsar (and its nebula) is formed inside
or close to a high density regions of a molecular cloud. We apply a recent
model for the gamma radiation of pulsar wind nebulae (PWN), which includes not
only radiation processes due to injected leptons but also processes due to
injection of relativistic hadrons, in order to calculate the expected gamma-ray
emission from such interacting PWNe. The example calculations have been
performed for two objects of this type from which directions TeV gamma-ray
sources have recently been observed (IC443 and W41). We show that the gamma-ray
emission below a few TeV can be produced by leptons accelerated in the past in
the vicinity of the pulsars. gamma-rays with energies above ~10 TeV can be
produced by hadrons interacting with the matter inside the supernova remnant
and surrounding dense clouds. In contrary to the low energy TeV emission, this
high energy TeV emission should be correlated with the location of dense clouds
able to capture hadrons due to their strong magnetic fields.Comment: Proceedings of the 30th ICRC, Merida, Mexico, 2007, in pres
Radio Emission and Particle Acceleration in SN 1993J
The radio light curves of SN 1993J are found to be well fit by a synchrotron
spectrum, suppressed by external free-free absorption and synchrotron
self-absorption. A standard r^-2 circumstellar medium is assumed, and found to
be adequate. The magnetic field and number density of relativistic electrons
behind the shock are determined. The strength of the magnetic field argues
strongly for turbulent amplification behind the shock. The ratio of the
magnetic and thermal energy density behind the shock is ~0.14. Synchrotron and
Coulomb cooling dominate the losses of the electrons. The injected electron
spectrum has a power law index -2.1, consistent with diffusive shock
acceleration, and the number density scales with the thermal electron energy
density. The total energy density of the relativistic electrons is, if
extrapolated to gamma ~ 1, ~ 5x10^-4 of the thermal energy density. The
free-free absorption required is consistent with previous calculations of the
circumstellar temperature of SN 1993J, T_e ~ (2-10)x10^5 K. The relative
importance of free-free absorption, Razin suppression, and the synchrotron
self-absorption effect for other supernovae are briefly discussed. Guidelines
for the modeling and interpretation of VLBI observations are given.Comment: accepted for Ap.
Yet Another Model of Gamma-Ray Bursts
Sari and Piran have demonstrated that the time structure of gamma-ray bursts
must reflect the time structure of their energy release. A model which
satisfies this condition uses the electrodynamic emission of energy by the
magnetized rotating ring of dense matter left by neutron star coalescence; GRB
are essentially fast, high field, differentially rotating pulsars. The energy
densities are large enough that the power appears as an outflowing equilibrium
pair plasma, which produces the burst by baryon entrainment and subsequent
internal shocks. I estimate the magnetic field and characteristic time scale
for its rearrangement, which determines the observed time structure of the
burst. There may be quasi-periodic oscillations at the rotational frequencies,
which are predicted to range up to 5770 Hz (in a local frame). This model is
one of a general class of electrodynamic accretion models which includes the
Blandford and Lovelace model of AGN, and which can also be applied to black
hole X-ray sources of stellar mass. The apparent efficiency of nonthermal
particle acceleration is predicted to be 10--50%, but higher values are
possible if the underlying accretion flow is super-Eddington. Applications to
high energy gamma-ray observations of AGN are briefly discussed.Comment: 21pp, latex, uses aaspp4.st
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