J. R. Jokipii

Corotating variations of cosmic rays near the South heliospheric pole.

Three-dimensional simulations of the heliospheric modulation of galactic cosmic ray protons show that corotating variations in the intensity can persist to quite high heliographic latitudes. Variations are seen at latitudes considerably higher than the maximum latitude extension of the heliographic current sheet, in regions where the solar wind velocity and magnetic field show no significant variation. Similar conclusions may apply also to lower energy particles, which may be accelerated at lower latitudes. Cosmic ray variations caused by corotating interaction regions present at low heliographic latitudes can propagate to significantly higher latitudes.

Global Anisotropies in TeV Cosmic Rays Related to the Sun’s Local Galactic Environment from IBEX

Ordering Cosmic Rays Earth and other planets are constantly bombarded by cosmic rays (charged particles from the cosmos). The flux of very-high-energy cosmic rays varies according to where we look in the sky. Schwadron et al. (p. 988, published online 13 February) show that recent measurements of the local interstellar parameters by NASAs Interstellar Boundary Explorer satellite are consistent with observed cosmic ray anisotropies at tera–electron volt energies, implying that local interstellar conditions play a role in ordering very-high-energy cosmic rays in our cosmic vicinity. Local interstellar conditions play a role in ordering very-high-energy cosmic rays in the Sun’s immediate environment. Observations with the Interstellar Boundary Explorer (IBEX) have shown enhanced energetic neutral atom (ENA) emission from a narrow, circular ribbon likely centered on the direction of the local interstellar medium (LISM) magnetic field. Here, we show that recent determinations of the local interstellar velocity, based on interstellar atom measurements with IBEX, are consistent with the interstellar modulation of high-energy (tera–electron volts, TeV) cosmic rays and diffusive propagation from supernova sources revealed in global anisotropy maps of ground-based high-energy cosmic-ray observatories (Milagro, Asγ, and IceCube). Establishing a consistent local interstellar magnetic field direction using IBEX ENAs at hundreds to thousands of eV and galactic cosmic rays at tens of TeV has wide-ranging implications for the structure of our heliosphere and its interactions with the LISM, which is particularly important at the time when the Voyager spacecraft are leaving our heliosphere.

A determination of the mass of Sagittarius A * from its radio spectral and source size measurements

There is growing evidence that Sgr A* may be a million solar mass black hole accreting from the Galactic center wind. A consideration of the spectral and source size characteristics associated with this process can offer at least two distinct means of inferring the mass M, complementing the more traditional dynamical arguments. We show that M is unmistakably correlated with both the radio spectral index and the critical wavelength below which the intrinsic source size dominates over the angular broadening due to scattering in the interstellar medium. Current observations can already rule out a mass much in excess of 2 x 10 exp 6 solar masses and suggest a likely value close to 1 x 10 exp 6 solar masses, in agreement with an earlier study matching the radio and high-energy spectral components. We anticipate that such a mass may be confirmed with the next generation of source-size observations using milliarcsecond angular resolution at 0.5 - 1 cm wavelengths.

PARTICLE ACCELERATION AT LOW CORONAL COMPRESSION REGIONS AND SHOCKS

We present a study on particle acceleration in the low corona associated with the expansion and acceleration of coronal mass ejections (CMEs). Because CME expansion regions low in the corona are effective accelerators over a finite spatial region, we show that there is a rigidity regime where particles effectively diffuse away and escape from the acceleration sites using analytic solutions to the Parker transport equation. This leads to the formation of broken power-law distributions. Based on our analytic solutions, we find a natural ordering of the break energy and second power-law slope (above the break energy) as a function of the scattering characteristics. These relations provide testable predictions for the particle acceleration from low in the corona. Our initial analysis of solar energetic particle observations suggests a range of shock compression ratios and rigidity dependencies that give rise to the solar energetic particle (SEP) events studied. The wide range of characteristics inferred suggests competing mechanisms at work in SEP acceleration. Thus, CME expansion and acceleration in the low corona may naturally give rise to rapid particle acceleration and broken power-law distributions in large SEP events.

A NEW MODEL for the HELIOSPHERE'S "iBEX RIBBON"

We present a model for the narrow, ribbon-like enhancement in the emission of ~keV energetic neutral atoms (ENA) coming from the outer heliosphere, coinciding roughly with the plane of the very local interstellar magnetic field (LISMF). We show that the pre-existing turbulent LISMF has sufficient amplitude in magnitude fluctuations to efficiently trap ions with initial pitch-angles near 90°, primarily by magnetic mirroring, leading to a narrow region of enhanced pickup-proton intensity. The pickup protons interact with cold interstellar hydrogen to produce ENAs seen at 1 AU. The computed width of the resulting ribbon of emission is consistent with observations. We also present results from a numerical model that are also generally consistent with the observations. Our interpretation relies only on the pre-existing turbulent interstellar magnetic field to trap the pickup protons. This leads to a broader local pitch-angle distribution compared to that of a ring. Our numerical model also predicts that the ribbon is double-peaked with a central depression. This is a further consequence of the (primarily) magnetic mirroring of pickup ions with pitch-angles close to 90° in the pre-existing, turbulent interstellar magnetic field.

EVOLUTION OF HIGH-ENERGY PARTICLE DISTRIBUTION IN MATURE SHELL-TYPE SUPERNOVA REMNANTS

Strategic Priority Research Program, of the Chinese Academy of Sciences [XDB09000000]; Emergence of Cosmological Structures, of the Chinese Academy of Sciences [XDB09000000]; Key Laboratory of Particle Astrophysics of Yunnan Province [2015DG035]; NSFC [11173064, 11233001, 11233008]; National Natural Science Foundation of China (NSFC) [11433004]