31 research outputs found
Superbubble Origin of Cosmic Rays
After a hundred years of searching for the origin of cosmic rays, where and
how they are made has finally become clear. Here we briefly trace that odyssey
through both astronomical observations and cosmic ray measurements.Comment: 5 pages, 3 figures, Invited paper in Centenary Symposium 2012:
Discovery of Cosmic Rays (AIP Conf. Proc.
The Origin of Cosmic Rays: How Their Composition Defines Their Sources and Sites, and the Processes of Their Mixing, Injection and Acceleration
Galactic cosmic-ray source compositions, (Z/H)GCRS from H to Pb and ~10^8 -
10^14 eV, differ from solar-local interstellar, (Z/H)SS or (Z/H)ISM by
~20-200x. Both are mostly just mixes of core collapse (CCSN) and thermonuclear
(SN Ia) supernova ejecta. The (Z/H)ISM come from steady unbiased accumulation
over Gyrs. But the cosmic ray mass mixing ratio, universal ISM/CCSN ~4:1 of
swept-up ISM and ~10x metallicity ejecta show that (Z/H)GCRS come from basic
Sedov-Taylor bulk mixing of homologous, expanding CCSN in their OB cluster
self-generated superbubbles, further enriched by highly biased grain-sputtering
injection during diffusive shock acceleration (DSA). Moreover, this mixing
ratio now reveals that the cosmic rays are primarily accelerated as their
evolving reverse shock radius and energy passes through their maxima.
Refractories and volatiles, first deposited in fast ejecta and ISM grains in
freely expanding ejecta, are simultaneously Coulomb-sputtered FCS by turbulent
H and He as suprathermal ions into DSA that carries them to cosmic-ray
energies. This bulk mixing selectively increases source mix abundancies (Z/H)SM
/ (Z/H)SS by ~2-10; and injection by grain condensation and implantation
fractions FGC, by another ~6, while Z^0.67 Coulomb grain sputtering enrichments
FCS give an added ~4-20. Applying these basic processes of mixing and injection
to solar system (Z/H)SS produces grain-injected, source-mix (Z/H)SMGI that
match major cosmic ray abundances (Z/H)GCRS to within 35 % with no free
parameters. Independently confirming grain injection, (Z/H)GCRS shows no
detectable contribution of Fe from SN Ia, although producing ~1/2 Fe in ISM,
but there is also no dust in SN Ia remnants, unlike CCSN.Comment: 44 pages, 11 figures, 3 table
Compton backscattered annihilation line emission: A new diagnostic of accreting compact sources
It is shown that Compton scattering of 511 keV electron-positron annihilation radiation produces a line like feature at approx. 170 keV from backscattered photons. Assuming a simple model of an accretion disk around a compact source, the spectrum is explored of the spectrum of Compton scattered annihilation line emission for a range of conditions. It is further shown that such Compton baskscattering of annihilation line emission from the inner edge of an accretion disk could account for the previously unidentified 170 keV line emission and high energy continuum observed from a variable, compact source, or sources, of annihilation radiation near the Galactic Center. Identification of the observed 170 keV line as an annihilation line reflection feature provides strong new evidence that the source of the emission is an accreting compact object. Further study of these features in existing spectra and in forthcoming GRO observation of these and other sources can provide unique new diagnostics of the innermost regions of accretion disks around compact objects
Determining the solar-flare photospheric scale height from SMM gamma-ray measurements
A connected series of Monte Carlo programs was developed to make systematic calculations of the energy, temporal and angular dependences of the gamma-ray line and neutron emission resulting from such accelerated ion interactions. Comparing the results of these calculations with the Solar Maximum Mission/Gamma Ray Spectrometer (SMM/GRS) measurements of gamma-ray line and neutron fluxes, the total number and energy spectrum of the flare-accelerated ions trapped on magnetic loops at the Sun were determined and the angular distribution, pitch angle scattering, and mirroring of the ions on loop fields were constrained. Comparing the calculations with measurements of the time dependence of the neutron capture line emission, a determination of the He-3/H ratio in the photosphere was also made. The diagnostic capabilities of the SMM/GRS measurements were extended by developing a new technique to directly determine the effective photospheric scale height in solar flares from the neutron capture gamma-ray line measurements, and critically test current atmospheric models in the flare region
Light Elements and Cosmic Rays in the Early Galaxy
We derive constraints on the cosmic rays responsible for the Be and part of
the B observed in stars formed in the early Galaxy: the cosmic rays cannot be
accelerated from the ISM; their energy spectrum must be relatively hard (the
bulk of the nuclear reactions should occur at 30 MeV/nucl); and only
10 erg/SNII in high metallicity, accelerated particle kinetic energy
could suffice to produce the Be and B. The reverse SNII shock could accelerate
the particles.Comment: 5 pages LATEX using paspconf.sty file with one embedded eps figure
using psfig. In press, Proc. Goddard High Resolution Spectrograph Symposium,
PASP, 199
Temporal Variations of Strength and Location of the South Atlantic Anomaly as Measured by RXTE
The evolution of the particle background at an altitude of ~540 km during the
time interval between 1996 and 2007 is studied using the particle monitor of
the High Energy X-ray Timing Experiment on board NASA's Rossi X-ray Timing
Explorer. A special emphasis of this study is the location and strength of the
South Atlantic Anomaly (SAA). The size and strength of the SAA are
anti-correlated with the the 10.7 cm radio flux of the Sun, which leads the SAA
strength by ~1 year reflecting variations in solar heating of the upper
atmosphere. The location of the SAA is also found to drift westwards with an
average drift rate of about 0.3 deg/yr following the drift of the geomagnetic
field configuration. Superimposed to this drift rate are irregularities, where
the SAA suddenly moves eastwards and where furthermore the speed of the drift
changes. The most prominent of these irregularities is found in the second
quarter of 2003 and another event took place in 1999. We suggest that these
events are previously unrecognized manifestations of the geomagnetic jerks of
the Earth's magnetic field.Comment: 21 pages, 11 figures, accepted for publication in Earth and Planetary
Science Letter
Gamma Ray Lines from the Orion Complex
We show that the 4.44 and 6.13 MeV line emission observed with COMPTEL from
Orion is consistent with gamma ray spectra consisting of a mixture of narrow
and broad lines or spectra containing only broad lines. We employed several
accelerated particle compositions and showed that the current COMPTEL data in
the 3--7 MeV region alone cannot distinguish between the various possibilities.
However, the COMPTEL upper limits in the 1--3 MeV band favor a composition
similar to that of the winds of Wolf-Rayet stars of spectral type WC. The power
dissipated by the accelerated particles at Orion is about 4 10
erg s. These particles are not expected to produce significant amounts
of Al.Comment: 12 pages, uuencoded compressed postscript with 4 figures ApJL in
press 199