University of New Hampshire

About: University of New Hampshire is a education organization based out in Durham, New Hampshire, United States. It is known for research contribution in the topics: Population & Solar wind. The organization has 9379 authors who have published 24025 publications receiving 1020112 citations. The organization is also known as: UNH.

The Soft Gamma-Ray Spectral Variability of Cygnus X-1

Abstract: We have used observations of Cyg X-1 from the Compton Gamma Ray Observatory and BeppoSAX to study the variation in the MeV γ-ray emission between the hard and soft spectral states, using spectra that cover the energy range from 20 keV up to 10 MeV. These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux decreases during the soft state, the flux at energies above 1 MeV increases, resulting in a significantly harder γ-ray spectrum at energies above 1 MeV. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft γ-ray energies. These data extend this picture, for the first time, to energies above 1 MeV. We have used two different hybrid thermal/nonthermal Comptonization models to fit broadband spectral data obtained in both the hard and soft spectral states. These fits provide a quantitative estimate of the electron distribution and allow us to probe the physical changes that take place during transitions between the low and high X-ray states. We find that there is a significant increase (by a factor of ~4) in the bolometric luminosity as the source moves from the hard state to the soft state. Furthermore, the presence of a nonthermal tail in the Comptonizing electron distribution provides significant constraints on the magnetic field in the source region.

Optimization and the matching law as accounts of instrumental behavior.

Abstract: The interaction between instrumental behavior and environment can be conveniently described at a molar level as a feedback system. Two different possible theories, the matching law and optimization, differ primarily in the reference criterion they suggest for the system. Both offer accounts of most of the known phenomena of performance on concurrent and single variable-interval and variable-ratio schedules. The matching law appears stronger in describing concurrent performances, whereas optimization appears stronger in describing performance on single schedules.

Extended magnetic reconnection at the Earth's magnetopause from detection of bi-directional jets

Abstract: Magnetic reconnection is a process that converts magnetic energy into bi-directional plasma jets; it is believed to be the dominant process by which solar-wind energy enters the Earth's magnetosphere1,2. This energy is subsequently dissipated by magnetic storms and aurorae3,4. Previous single-spacecraft observations5,6,7 revealed only single jets at the magnetopause—while the existence of a counter-streaming jet was implicitly assumed, no experimental confirmation was available. Here we report in situ two-spacecraft observations of bi-directional jets at the magnetopause, finding evidence for a stable and extended reconnection line; the latter implies substantial entry of the solar wind into the magnetosphere. We conclude that reconnection is determined by large-scale interactions between the solar wind and the magnetosphere, rather than by local conditions at the magnetopause.

Comparison of Interstellar Boundary Explorer Observations with 3D Global Heliospheric Models

Abstract: The influence of the Sun is felt well beyond the orbits of the planets. The solar wind is a stream of charged particles emanating from the Sun that carves a bubble in interstellar space known as the heliosphere and shrouds the entire solar system. The edge of the heliosphere, the region where the solar wind interacts with interstellar space, is largely unexplored. Voyager 1 and 2 crossed this boundary in 2004 and 2007, respectively, providing detailed but only localized information. In this issue (see the cover), McComas et al. (p. [959][1], published online 15 October), Fuselier et al. (p. [962][2], published online 15 October), Funsten et al. (p. [964][3], published online 15 October), and Mobius et al. (p. [969][4], published online 15 October) present data taken by NASA's Interstellar Boundary Explorer (IBEX). Since early 2009, IBEX has been building all-sky maps of the emissions of energetic neutral atoms produced at the boundary between the heliosphere and the interstellar medium. These maps have unexpectedly revealed a narrow band of emission that bisects the two Voyager locations at energies ranging from 0.2 to 6 kiloelectron volts. Emissions from the band are two- to threefold brighter than outside the band, in contrast to current models that predict much smaller variations across the sky. By comparing the IBEX observations with models of the heliosphere, Schwadron et al. (p. [966][5], published online 15 October) show that to date no model fully explains the observations. The model they have developed suggests that the interstellar magnetic field plays a stronger role than previously thought. In addition to the all-sky maps, IBEX measured the signatures of H, He, and O flowing into the heliosphere from the interstellar medium. In a related report, Krimigis et al. (p. [971][6], published online 15 October) present an all-sky image of energetic neutral atoms with energies ranging between 6 and 13 kiloelectron volts obtained with the Ion and Neutral Camera onboard the Cassini spacecraft orbiting Saturn. It shows that parts of the structure observed by IBEX extend to high energies. These data indicate that the shape of the heliosphere is not consistent with that of a comet aligned in the direction of the Sun's travel through the galaxy as was previously thought. [1]: /lookup/doi/10.1126/science.1180906 [2]: /lookup/doi/10.1126/science.1180981 [3]: /lookup/doi/10.1126/science.1180927 [4]: /lookup/doi/10.1126/science.1180971 [5]: /lookup/doi/10.1126/science.1180986 [6]: /lookup/doi/10.1126/science.1181079