12,544 research outputs found
Cosmic Ray acceleration and Balmer emission from SNR 0509-67.5
Context: Observation of Balmer lines from the region around the forward shock
of supernova remnants may provide precious information on the shock dynamics
and on the efficiency of particle acceleration at the shock.
Aims: We calculate the Balmer line emission and the shape of the broad Balmer
line for parameter values suitable for SNR 0509-67.5, as a function of the
cosmic ray acceleration efficiency and of the level of thermal equilibration
between electrons and protons behind the shock. This calculation aims at using
the width of the broad Balmer line emission to infer the cosmic ray
acceleration efficiency in this remnant.
Methods: We use the recently developed non-linear theory of diffusive shock
acceleration in the presence of neutrals. The semi-analytical approach that we
developed includes a description of magnetic field amplification as due to
resonant streaming instability, the dynamical reaction of both accelerated
particles and turbulent magnetic field on the shock, and all channels of
interaction between neutral atoms and background plasma that change the shock
dynamics.
Results: We achieve a quantitative assessment of the CR acceleration
efficiency in SNR 0509-67.5 as a function of the shock velocity and different
levels of electron-proton thermalization in the shock region. If the shock
moves faster than ~4500 km/s, one can conclude that particle acceleration must
be taking place with efficiency of several tens of percent. For lower shock
velocity the evidence for particle acceleration becomes less clear because of
the uncertainty in the electron-ion equilibration downstream. We also discuss
the role of future measurements of the narrow Balmer line.Comment: 7 pages, 5 figure. Accepted for publication in Astronomy &
Astrophysic
On the Coexistence Magnetism/Superconductivity in the Heavy-Fermion Superconductor CePtSi
The interplay between magnetism and superconductivity in the newly discovered
heavy-fermion superconductor CePtSi has been investigated using the
zero-field SR technique. The SR data indicate that the whole muon
ensemble senses spontaneous internal fields in the magnetic phase,
demonstrating that magnetism occurs in the whole sample volume. This points to
a microscopic coexistence between magnetism and heavy-fermion
superconductivity.Comment: Final version, new figure structure, references correcte
Broad Balmer line emission and cosmic ray acceleration efficiency in supernova remnant shocks
Balmer emission may be a powerful diagnostic tool to test the paradigm of
cosmic ray (CR) acceleration in young supernova remnant (SNR) shocks. The width
of the broad Balmer line is a direct indicator of the downstream plasma
temperature. In case of efficient particle acceleration an appreciable fraction
of the total kinetic energy of the plasma is channeled into CRs, therefore the
downstream temperature decreases and so does the broad Balmer line width. This
width also depends on the level of thermal equilibration between ions and
neutral hydrogen atoms in the downstream. Since in general in young SNR shocks
only a few charge exchange (CE) reactions occur before ionization,
equilibration between ions and neutrals is not reached, and a kinetic
description of the neutrals is required in order to properly compute Balmer
emission.
We provide a method for the calculation of Balmer emission using a
self-consistent description of the shock structure in the presence of neutrals
and CRs. We use a recently developed semi-analytical approach, where neutral
particles, ionized plasma, accelerated particles and magnetic fields are all
coupled together through the mass, momentum and energy flux conservation
equations. The distribution of neutrals is obtained from the full Boltzmann
equation in velocity space, coupled to Maxwellian ions through ionization and
CE processes. The computation is also improved with respect to previous work
thanks to a better approximation for the atomic interaction rates. We find that
for shock speeds >2500km/s the distribution of broad neutrals never approaches
a Maxwellian and its moments differ from those of the ionized component. These
differences reflect into a smaller FWHM than predicted in previous
calculations, where thermalization was assumed. The method presented here
provides a realistic estimate of particle acceleration efficiency in Balmer
dominated shocks.Comment: 6 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
Cosmic Ray acceleration and Balmer emission from RCW 86 (G315.4-2.3)
Context. Observation of Balmer lines from the region around the forward shock
of supernova remnants (SNR) may provide valuable information on the shock
dynamics and the efficiency of particle acceleration at the shock.
Aims. We calculated the Balmer line emission and the shape of the broad
Balmer line for parameter values suitable for SNR RCW 86 (G315.4-2.3) as a
function of the cosmic-ray (CR) acceleration efficiency and of the level of
thermal equilibration between electrons and protons behind the shock. This
calculation aims at using the width of the broad Balmer-line emission to infer
the CR acceleration efficiency in this remnant.
Methods. We used the recently developed nonlinear theory of diffusive
shock-acceleration in the presence of neutrals. The semianalytical approach we
developed includes a description of magnetic field amplification as due to
resonant streaming instability, the dynamical reaction of accelerated particles
and the turbulent magnetic field on the shock, and all channels of interaction
between neutral hydrogen atoms and background ions that are relevant for the
shock dynamics.
Results. We derive the CR acceleration efficiency in the SNR RCW 86 from the
Balmer emission. Since our calculation used recent measurements of the shock
proper motion, the results depend on the assumed distance to Earth. For a
distance of 2 kpc the measured width of the broad Balmer line is compatible
with the absence of CR acceleration. For a distance of 2.5 kpc, which is a
widely used value in current literature, a CR acceleration efficiency of 5-30%
is obtained, depending upon the electron-ion equilibration and the ionization
fraction upstream of the shock. By combining information on Balmer emission
with the measured value of the downstream electron temperature, we constrain
the CR acceleration efficiency to be ~20%.Comment: 7 pages, 6 figures. Accepted for publication in A&A (minor changes to
match the published version
A binocular-type atmospheric interaction generating sequential exotic features
A cosmic-ray induced nuclear event is presented, which is of clear binocular-type and contains several exotic features through its passage in the atmosphere and the emulsion chamber
A halo event created at 200 m above the Chacaltaya emulsion chamber
The results of analysis on a cosmic-ray induced nuclear event with the total visible energy approx. = 1300 TeV which is characterized by the central (halo) part of a strong energy concentration and the outer part of a large lateral spread are presented. The event (named as P06) was detected in the 18th two-storied emulsion chamber exposed at Chacaltaya by Brasil-Japan Collaboration. As the nuclear emulsion plates were inserted at every layer of the concerned blocks in the upper and the lower chambers together with RR- and N-type X-ray films, it is possible to study the details of the event. Some results on P06 have already been reported 1 based on the general measurement of opacity on N-type X-ray films: (1) the total energy of halo is approx. = 1000 TeV; (2) the shower transition reaches its maximum at approx. 16 cu; and (3) the radius of halo is 6.5 mm (at the level of 10 to the 6th power electrons/sq.cm.). The results in more details will be described
Facilitating the exploitation of ERTS-1 imagery using snow enhancement techniques
The author has identified the following significant results. The applications of ERTS-1 imagery for geological fracture mapping regardless of season has been repeatedly confirmed. The enhancement provided by a differential cover of snow increases the number and length of fracture-lineaments which can be detected with ERTS-1 data and accelerates the fracture mapping process for a variety of practical applications. The geological mapping benefits of the program will be realized in geographic areas where data are most needed - complex glaciated terrain and areas of deep residual soils. ERTS-1 derived fracture-lineament maps which provide detail well in excess of existing geological maps are not available in the Massachusetts-Connecticut area. The large quantity of new data provided by ERTS-1 may accelerate and improve field mapping now in progress in the area. Numerous other user groups have requested data on the techniques. This represents a major change in operating philosophy for groups who to data judged that snow obscured geological detail
Atmospheric interactions detected in both the upper and the lower chambers at Chacaltaya
The cosmic ray interactions in the energy region 10 to the 13th power to 10 to the 17th power eV were studied by emulsion chambers exposed at Chacaltaya, 5220 m above sea-level. The chambers have a two-storied structure, and the events observed in both chambers give important informations on these phenomena. The first Centauro event was detected as a small shower at the bottom of the upper chamber and as a big fraction of energy deposit in the lower chamber, which indicates a high contribution of hadronic showers. Results of the events with continuation in the rather low energy region are described
- …